FreeBSD/Linux Kernel Cross Reference
sys/dev/sio/sio.c

     /*-
      * Copyright (c) 1991 The Regents of the University of California.
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
      *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      from: @(#)com.c 7.5 (Berkeley) 5/16/91
     *      from: i386/isa sio.c,v 1.234
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_comconsole.h"
    #include "opt_compat.h"
    #include "opt_gdb.h"
    #include "opt_kdb.h"
    #include "opt_sio.h"
    
    /*
     * Serial driver, based on 386BSD-0.1 com driver.
     * Mostly rewritten to use pseudo-DMA.
     * Works for National Semiconductor NS8250-NS16550AF UARTs.
     * COM driver, based on HP dca driver.
     *
     * Changes for PC Card integration:
     *      - Added PC Card driver table and handlers
     */
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/bus.h>
    #include <sys/conf.h>
    #include <sys/fcntl.h>
    #include <sys/interrupt.h>
    #include <sys/kdb.h>
    #include <sys/kernel.h>
    #include <sys/limits.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/module.h>
    #include <sys/mutex.h>
    #include <sys/proc.h>
    #include <sys/reboot.h>
    #include <sys/serial.h>
    #include <sys/sysctl.h>
    #include <sys/syslog.h>
    #include <sys/tty.h>
    #include <machine/bus.h>
    #include <sys/rman.h>
    #include <sys/timepps.h>
    #include <sys/uio.h>
    #include <sys/cons.h>
    
    #include <isa/isavar.h>
    
    #include <machine/resource.h>
    
    #include <dev/sio/sioreg.h>
    #include <dev/sio/siovar.h>
    
    #ifdef COM_ESP
    #include <dev/ic/esp.h>
    #endif
    #include <dev/ic/ns16550.h>
    
    #define LOTS_OF_EVENTS  64      /* helps separate urgent events from input */
    
    #ifdef COM_MULTIPORT
    /* checks in flags for multiport and which is multiport "master chip"
     * for a given card
     */
    #define COM_ISMULTIPORT(flags)  ((flags) & 0x01)
    #define COM_MPMASTER(flags)     (((flags) >> 8) & 0x0ff)
    #define COM_NOTAST4(flags)      ((flags) & 0x04)
    #else
    #define COM_ISMULTIPORT(flags)  (0)
    #endif /* COM_MULTIPORT */
   
   #define COM_C_IIR_TXRDYBUG      0x80000
   #define COM_CONSOLE(flags)      ((flags) & 0x10)
   #define COM_DEBUGGER(flags)     ((flags) & 0x80)
   #define COM_FIFOSIZE(flags)     (((flags) & 0xff000000) >> 24)
   #define COM_FORCECONSOLE(flags) ((flags) & 0x20)
   #define COM_IIR_TXRDYBUG(flags) ((flags) & COM_C_IIR_TXRDYBUG)
   #define COM_LLCONSOLE(flags)    ((flags) & 0x40)
   #define COM_LOSESOUTINTS(flags) ((flags) & 0x08)
   #define COM_NOFIFO(flags)       ((flags) & 0x02)
   #define COM_NOPROBE(flags)      ((flags) & 0x40000)
   #define COM_NOSCR(flags)        ((flags) & 0x100000)
   #define COM_PPSCTS(flags)       ((flags) & 0x10000)
   #define COM_ST16650A(flags)     ((flags) & 0x20000)
   #define COM_TI16754(flags)      ((flags) & 0x200000)
   
   #define sio_getreg(com, off) \
           (bus_space_read_1((com)->bst, (com)->bsh, (off)))
   #define sio_setreg(com, off, value) \
           (bus_space_write_1((com)->bst, (com)->bsh, (off), (value)))
   
   /*
    * com state bits.
    * (CS_BUSY | CS_TTGO) and (CS_BUSY | CS_TTGO | CS_ODEVREADY) must be higher
    * than the other bits so that they can be tested as a group without masking
    * off the low bits.
    *
    * The following com and tty flags correspond closely:
    *      CS_BUSY         = TS_BUSY (maintained by comstart(), siopoll() and
    *                                 comstop())
    *      CS_TTGO         = ~TS_TTSTOP (maintained by comparam() and comstart())
    *      CS_CTS_OFLOW    = CCTS_OFLOW (maintained by comparam())
    *      CS_RTS_IFLOW    = CRTS_IFLOW (maintained by comparam())
    * TS_FLUSH is not used.
    * XXX I think TIOCSETA doesn't clear TS_TTSTOP when it clears IXON.
    * XXX CS_*FLOW should be CF_*FLOW in com->flags (control flags not state).
    */
   #define CS_BUSY         0x80    /* output in progress */
   #define CS_TTGO         0x40    /* output not stopped by XOFF */
   #define CS_ODEVREADY    0x20    /* external device h/w ready (CTS) */
   #define CS_CHECKMSR     1       /* check of MSR scheduled */
   #define CS_CTS_OFLOW    2       /* use CTS output flow control */
   #define CS_ODONE        4       /* output completed */
   #define CS_RTS_IFLOW    8       /* use RTS input flow control */
   #define CSE_BUSYCHECK   1       /* siobusycheck() scheduled */
   
   static  char const * const      error_desc[] = {
   #define CE_OVERRUN                      0
           "silo overflow",
   #define CE_INTERRUPT_BUF_OVERFLOW       1
           "interrupt-level buffer overflow",
   #define CE_TTY_BUF_OVERFLOW             2
           "tty-level buffer overflow",
   };
   
   #define CE_NTYPES                       3
   #define CE_RECORD(com, errnum)          (++(com)->delta_error_counts[errnum])
   
   /* types.  XXX - should be elsewhere */
   typedef u_int   Port_t;         /* hardware port */
   typedef u_char  bool_t;         /* boolean */
   
   /* queue of linear buffers */
   struct lbq {
           u_char  *l_head;        /* next char to process */
           u_char  *l_tail;        /* one past the last char to process */
           struct lbq *l_next;     /* next in queue */
           bool_t  l_queued;       /* nonzero if queued */
   };
   
   /* com device structure */
   struct com_s {
           u_char  state;          /* miscellaneous flag bits */
           u_char  cfcr_image;     /* copy of value written to CFCR */
   #ifdef COM_ESP
           bool_t  esp;            /* is this unit a hayes esp board? */
   #endif
           u_char  extra_state;    /* more flag bits, separate for order trick */
           u_char  fifo_image;     /* copy of value written to FIFO */
           bool_t  hasfifo;        /* nonzero for 16550 UARTs */
           bool_t  loses_outints;  /* nonzero if device loses output interrupts */
           u_char  mcr_image;      /* copy of value written to MCR */
   #ifdef COM_MULTIPORT
           bool_t  multiport;      /* is this unit part of a multiport device? */
   #endif /* COM_MULTIPORT */
           bool_t  no_irq;         /* nonzero if irq is not attached */
           bool_t  gone;           /* hardware disappeared */
           bool_t  poll;           /* nonzero if polling is required */
           bool_t  poll_output;    /* nonzero if polling for output is required */
           bool_t  st16650a;       /* nonzero if Startech 16650A compatible */
           int     unit;           /* unit number */
           u_int   flags;          /* copy of device flags */
           u_int   tx_fifo_size;
   
           /*
            * The high level of the driver never reads status registers directly
            * because there would be too many side effects to handle conveniently.
            * Instead, it reads copies of the registers stored here by the
            * interrupt handler.
            */
           u_char  last_modem_status;      /* last MSR read by intr handler */
           u_char  prev_modem_status;      /* last MSR handled by high level */
   
           u_char  *ibuf;          /* start of input buffer */
           u_char  *ibufend;       /* end of input buffer */
           u_char  *ibufold;       /* old input buffer, to be freed */
           u_char  *ihighwater;    /* threshold in input buffer */
           u_char  *iptr;          /* next free spot in input buffer */
           int     ibufsize;       /* size of ibuf (not include error bytes) */
           int     ierroff;        /* offset of error bytes in ibuf */
   
           struct lbq      obufq;  /* head of queue of output buffers */
           struct lbq      obufs[2];       /* output buffers */
   
           bus_space_tag_t         bst;
           bus_space_handle_t      bsh;
   
           Port_t  data_port;      /* i/o ports */
   #ifdef COM_ESP
           Port_t  esp_port;
   #endif
           Port_t  int_ctl_port;
           Port_t  int_id_port;
           Port_t  modem_ctl_port;
           Port_t  line_status_port;
           Port_t  modem_status_port;
   
           struct tty      *tp;    /* cross reference */
   
           struct  pps_state pps;
           int     pps_bit;
   #ifdef ALT_BREAK_TO_DEBUGGER
           int     alt_brk_state;
   #endif
   
           u_long  bytes_in;       /* statistics */
           u_long  bytes_out;
           u_int   delta_error_counts[CE_NTYPES];
           u_long  error_counts[CE_NTYPES];
   
           u_long  rclk;
   
           struct resource *irqres;
           struct resource *ioportres;
           int     ioportrid;
           void    *cookie;
   
           /*
            * Data area for output buffers.  Someday we should build the output
            * buffer queue without copying data.
            */
           u_char  obuf1[256];
           u_char  obuf2[256];
   };
   
   #ifdef COM_ESP
   static  int     espattach(struct com_s *com, Port_t esp_port);
   #endif
   
   static  void    combreak(struct tty *tp, int sig);
   static  timeout_t siobusycheck;
   static  u_int   siodivisor(u_long rclk, speed_t speed);
   static  void    comclose(struct tty *tp);
   static  int     comopen(struct tty *tp, struct cdev *dev);
   static  void    sioinput(struct com_s *com);
   static  void    siointr1(struct com_s *com);
   static  int     siointr(void *arg);
   static  int     commodem(struct tty *tp, int sigon, int sigoff);
   static  int     comparam(struct tty *tp, struct termios *t);
   static  void    siopoll(void *);
   static  void    siosettimeout(void);
   static  int     siosetwater(struct com_s *com, speed_t speed);
   static  void    comstart(struct tty *tp);
   static  void    comstop(struct tty *tp, int rw);
   static  timeout_t comwakeup;
   
   char            sio_driver_name[] = "sio";
   static struct   mtx sio_lock;
   static int      sio_inited;
   
   /* table and macro for fast conversion from a unit number to its com struct */
   devclass_t      sio_devclass;
   #define com_addr(unit)  ((struct com_s *) \
                            devclass_get_softc(sio_devclass, unit)) /* XXX */
   
   int     comconsole = -1;
   static  volatile speed_t        comdefaultrate = CONSPEED;
   static  u_long                  comdefaultrclk = DEFAULT_RCLK;
   SYSCTL_ULONG(_machdep, OID_AUTO, conrclk, CTLFLAG_RW, &comdefaultrclk, 0, "");
   static  speed_t                 gdbdefaultrate = GDBSPEED;
   SYSCTL_UINT(_machdep, OID_AUTO, gdbspeed, CTLFLAG_RW,
               &gdbdefaultrate, GDBSPEED, "");
   static  u_int   com_events;     /* input chars + weighted output completions */
   static  Port_t  siocniobase;
   static  int     siocnunit = -1;
   static  void    *sio_slow_ih;
   static  void    *sio_fast_ih;
   static  int     sio_timeout;
   static  int     sio_timeouts_until_log;
   static  struct  callout_handle sio_timeout_handle
       = CALLOUT_HANDLE_INITIALIZER(&sio_timeout_handle);
   static  int     sio_numunits;
   
   #ifdef GDB
   static  Port_t  siogdbiobase = 0;
   #endif
   
   #ifdef COM_ESP
   /* XXX configure this properly. */
   /* XXX quite broken for new-bus. */
   static  Port_t  likely_com_ports[] = { 0x3f8, 0x2f8, 0x3e8, 0x2e8, };
   static  Port_t  likely_esp_ports[] = { 0x140, 0x180, 0x280, 0 };
   #endif
   
   /*
    * handle sysctl read/write requests for console speed
    * 
    * In addition to setting comdefaultrate for I/O through /dev/console,
    * also set the initial and lock values for the /dev/ttyXX device
    * if there is one associated with the console.  Finally, if the /dev/tty
    * device has already been open, change the speed on the open running port
    * itself.
    */
   
   static int
   sysctl_machdep_comdefaultrate(SYSCTL_HANDLER_ARGS)
   {
           int error, s;
           speed_t newspeed;
           struct com_s *com;
           struct tty *tp;
   
           newspeed = comdefaultrate;
   
           error = sysctl_handle_opaque(oidp, &newspeed, sizeof newspeed, req);
           if (error || !req->newptr)
                   return (error);
   
           comdefaultrate = newspeed;
   
           if (comconsole < 0)             /* serial console not selected? */
                   return (0);
   
           com = com_addr(comconsole);
           if (com == NULL)
                   return (ENXIO);
   
           tp = com->tp;
           if (tp == NULL)
                   return (ENXIO);
   
           /*
            * set the initial and lock rates for /dev/ttydXX and /dev/cuaXX
            * (note, the lock rates really are boolean -- if non-zero, disallow
            *  speed changes)
            */
           tp->t_init_in.c_ispeed  = tp->t_init_in.c_ospeed =
           tp->t_lock_in.c_ispeed  = tp->t_lock_in.c_ospeed =
           tp->t_init_out.c_ispeed = tp->t_init_out.c_ospeed =
           tp->t_lock_out.c_ispeed = tp->t_lock_out.c_ospeed = comdefaultrate;
   
           if (tp->t_state & TS_ISOPEN) {
                   tp->t_termios.c_ispeed =
                   tp->t_termios.c_ospeed = comdefaultrate;
                   s = spltty();
                   error = comparam(tp, &tp->t_termios);
                   splx(s);
           }
           return error;
   }
   
   SYSCTL_PROC(_machdep, OID_AUTO, conspeed, CTLTYPE_INT | CTLFLAG_RW,
               0, 0, sysctl_machdep_comdefaultrate, "I", "");
   TUNABLE_INT("machdep.conspeed", __DEVOLATILE(int *, &comdefaultrate));
   
   #define SET_FLAG(dev, bit) device_set_flags(dev, device_get_flags(dev) | (bit))
   #define CLR_FLAG(dev, bit) device_set_flags(dev, device_get_flags(dev) & ~(bit))
   
   /*
    *      Unload the driver and clear the table.
    *      XXX this is mostly wrong.
    *      XXX TODO:
    *      This is usually called when the card is ejected, but
    *      can be caused by a kldunload of a controller driver.
    *      The idea is to reset the driver's view of the device
    *      and ensure that any driver entry points such as
    *      read and write do not hang.
    */
   int
   siodetach(device_t dev)
   {
           struct com_s    *com;
   
           com = (struct com_s *) device_get_softc(dev);
           if (com == NULL) {
                   device_printf(dev, "NULL com in siounload\n");
                   return (0);
           }
           com->gone = TRUE;
           if (com->tp)
                   ttyfree(com->tp);
           if (com->irqres) {
                   bus_teardown_intr(dev, com->irqres, com->cookie);
                   bus_release_resource(dev, SYS_RES_IRQ, 0, com->irqres);
           }
           if (com->ioportres)
                   bus_release_resource(dev, SYS_RES_IOPORT, com->ioportrid,
                                        com->ioportres);
           if (com->ibuf != NULL)
                   free(com->ibuf, M_DEVBUF);
   
           device_set_softc(dev, NULL);
           free(com, M_DEVBUF);
           return (0);
   }
   
   int
   sioprobe(dev, xrid, rclk, noprobe)
           device_t        dev;
           int             xrid;
           u_long          rclk;
           int             noprobe;
   {
   #if 0
           static bool_t   already_init;
           device_t        xdev;
   #endif
           struct com_s    *com;
           u_int           divisor;
           bool_t          failures[10];
           int             fn;
           device_t        idev;
           Port_t          iobase;
           intrmask_t      irqmap[4];
           intrmask_t      irqs;
           u_char          mcr_image;
           int             result;
           u_long          xirq;
           u_int           flags = device_get_flags(dev);
           int             rid;
           struct resource *port;
   
           rid = xrid;
           port = bus_alloc_resource(dev, SYS_RES_IOPORT, &rid,
                                     0, ~0, IO_COMSIZE, RF_ACTIVE);
           if (!port)
                   return (ENXIO);
   
           com = malloc(sizeof(*com), M_DEVBUF, M_NOWAIT | M_ZERO);
           if (com == NULL) {
                   bus_release_resource(dev, SYS_RES_IOPORT, rid, port);
                   return (ENOMEM);
           }
           device_set_softc(dev, com);
           com->bst = rman_get_bustag(port);
           com->bsh = rman_get_bushandle(port);
           if (rclk == 0)
                   rclk = DEFAULT_RCLK;
           com->rclk = rclk;
   
           while (sio_inited != 2)
                   if (atomic_cmpset_int(&sio_inited, 0, 1)) {
                           mtx_init(&sio_lock, sio_driver_name, NULL,
                               (comconsole != -1) ?
                               MTX_SPIN | MTX_QUIET : MTX_SPIN);
                           atomic_store_rel_int(&sio_inited, 2);
                   }
   
   #if 0
           /*
            * XXX this is broken - when we are first called, there are no
            * previously configured IO ports.  We could hard code
            * 0x3f8, 0x2f8, 0x3e8, 0x2e8 etc but that's probably worse.
            * This code has been doing nothing since the conversion since
            * "count" is zero the first time around.
            */
           if (!already_init) {
                   /*
                    * Turn off MCR_IENABLE for all likely serial ports.  An unused
                    * port with its MCR_IENABLE gate open will inhibit interrupts
                    * from any used port that shares the interrupt vector.
                    * XXX the gate enable is elsewhere for some multiports.
                    */
                   device_t *devs;
                   int count, i, xioport;
   
                   devclass_get_devices(sio_devclass, &devs, &count);
                   for (i = 0; i < count; i++) {
                           xdev = devs[i];
                           if (device_is_enabled(xdev) &&
                               bus_get_resource(xdev, SYS_RES_IOPORT, 0, &xioport,
                                                NULL) == 0)
                                   outb(xioport + com_mcr, 0);
                   }
                   free(devs, M_TEMP);
                   already_init = TRUE;
           }
   #endif
   
           if (COM_LLCONSOLE(flags)) {
                   printf("sio%d: reserved for low-level i/o\n",
                          device_get_unit(dev));
                   bus_release_resource(dev, SYS_RES_IOPORT, rid, port);
                   device_set_softc(dev, NULL);
                   free(com, M_DEVBUF);
                   return (ENXIO);
           }
   
           /*
            * If the device is on a multiport card and has an AST/4
            * compatible interrupt control register, initialize this
            * register and prepare to leave MCR_IENABLE clear in the mcr.
            * Otherwise, prepare to set MCR_IENABLE in the mcr.
            * Point idev to the device struct giving the correct id_irq.
            * This is the struct for the master device if there is one.
            */
           idev = dev;
           mcr_image = MCR_IENABLE;
   #ifdef COM_MULTIPORT
           if (COM_ISMULTIPORT(flags)) {
                   Port_t xiobase;
                   u_long io;
   
                   idev = devclass_get_device(sio_devclass, COM_MPMASTER(flags));
                   if (idev == NULL) {
                           printf("sio%d: master device %d not configured\n",
                                  device_get_unit(dev), COM_MPMASTER(flags));
                           idev = dev;
                   }
                   if (!COM_NOTAST4(flags)) {
                           if (bus_get_resource(idev, SYS_RES_IOPORT, 0, &io,
                                                NULL) == 0) {
                                   xiobase = io;
                                   if (bus_get_resource(idev, SYS_RES_IRQ, 0,
                                       NULL, NULL) == 0)
                                           outb(xiobase + com_scr, 0x80);
                                   else
                                           outb(xiobase + com_scr, 0);
                           }
                           mcr_image = 0;
                   }
           }
   #endif /* COM_MULTIPORT */
           if (bus_get_resource(idev, SYS_RES_IRQ, 0, NULL, NULL) != 0)
                   mcr_image = 0;
   
           bzero(failures, sizeof failures);
           iobase = rman_get_start(port);
   
           /*
            * We don't want to get actual interrupts, just masked ones.
            * Interrupts from this line should already be masked in the ICU,
            * but mask them in the processor as well in case there are some
            * (misconfigured) shared interrupts.
            */
           mtx_lock_spin(&sio_lock);
   /* EXTRA DELAY? */
   
           /*
            * For the TI16754 chips, set prescaler to 1 (4 is often the
            * default after-reset value) as otherwise it's impossible to
            * get highest baudrates.
            */
           if (COM_TI16754(flags)) {
                   u_char cfcr, efr;
   
                   cfcr = sio_getreg(com, com_cfcr);
                   sio_setreg(com, com_cfcr, CFCR_EFR_ENABLE);
                   efr = sio_getreg(com, com_efr);
                   /* Unlock extended features to turn off prescaler. */
                   sio_setreg(com, com_efr, efr | EFR_EFE);
                   /* Disable EFR. */
                   sio_setreg(com, com_cfcr, (cfcr != CFCR_EFR_ENABLE) ? cfcr : 0);
                   /* Turn off prescaler. */
                   sio_setreg(com, com_mcr,
                              sio_getreg(com, com_mcr) & ~MCR_PRESCALE);
                   sio_setreg(com, com_cfcr, CFCR_EFR_ENABLE);
                   sio_setreg(com, com_efr, efr);
                   sio_setreg(com, com_cfcr, cfcr);
           }
   
           /*
            * Initialize the speed and the word size and wait long enough to
            * drain the maximum of 16 bytes of junk in device output queues.
            * The speed is undefined after a master reset and must be set
            * before relying on anything related to output.  There may be
            * junk after a (very fast) soft reboot and (apparently) after
            * master reset.
            * XXX what about the UART bug avoided by waiting in comparam()?
            * We don't want to to wait long enough to drain at 2 bps.
            */
           if (iobase == siocniobase)
                   DELAY((16 + 1) * 1000000 / (comdefaultrate / 10));
           else {
                   sio_setreg(com, com_cfcr, CFCR_DLAB | CFCR_8BITS);
                   divisor = siodivisor(rclk, SIO_TEST_SPEED);
                   sio_setreg(com, com_dlbl, divisor & 0xff);
                   sio_setreg(com, com_dlbh, divisor >> 8);
                   sio_setreg(com, com_cfcr, CFCR_8BITS);
                   DELAY((16 + 1) * 1000000 / (SIO_TEST_SPEED / 10));
           }
   
           /*
            * Enable the interrupt gate and disable device interrupts.  This
            * should leave the device driving the interrupt line low and
            * guarantee an edge trigger if an interrupt can be generated.
            */
   /* EXTRA DELAY? */
           sio_setreg(com, com_mcr, mcr_image);
           sio_setreg(com, com_ier, 0);
           DELAY(1000);            /* XXX */
           irqmap[0] = isa_irq_pending();
   
           /*
            * Attempt to set loopback mode so that we can send a null byte
            * without annoying any external device.
            */
   /* EXTRA DELAY? */
           sio_setreg(com, com_mcr, mcr_image | MCR_LOOPBACK);
   
           /*
            * Attempt to generate an output interrupt.  On 8250's, setting
            * IER_ETXRDY generates an interrupt independent of the current
            * setting and independent of whether the THR is empty.  On 16450's,
            * setting IER_ETXRDY generates an interrupt independent of the
            * current setting.  On 16550A's, setting IER_ETXRDY only
            * generates an interrupt when IER_ETXRDY is not already set.
            */
           sio_setreg(com, com_ier, IER_ETXRDY);
   
           /*
            * On some 16x50 incompatibles, setting IER_ETXRDY doesn't generate
            * an interrupt.  They'd better generate one for actually doing
            * output.  Loopback may be broken on the same incompatibles but
            * it's unlikely to do more than allow the null byte out.
            */
           sio_setreg(com, com_data, 0);
           if (iobase == siocniobase)
                   DELAY((1 + 2) * 1000000 / (comdefaultrate / 10));
           else
                   DELAY((1 + 2) * 1000000 / (SIO_TEST_SPEED / 10));
   
           /*
            * Turn off loopback mode so that the interrupt gate works again
            * (MCR_IENABLE was hidden).  This should leave the device driving
            * an interrupt line high.  It doesn't matter if the interrupt
            * line oscillates while we are not looking at it, since interrupts
            * are disabled.
            */
   /* EXTRA DELAY? */
           sio_setreg(com, com_mcr, mcr_image);
    
           /*
            * It seems my Xircom CBEM56G Cardbus modem wants to be reset
            * to 8 bits *again*, or else probe test 0 will fail.
            * gwk@sgi.com, 4/19/2001
            */
           sio_setreg(com, com_cfcr, CFCR_8BITS);
   
           /*
            * Some PCMCIA cards (Palido 321s, DC-1S, ...) have the "TXRDY bug",
            * so we probe for a buggy IIR_TXRDY implementation even in the
            * noprobe case.  We don't probe for it in the !noprobe case because
            * noprobe is always set for PCMCIA cards and the problem is not
            * known to affect any other cards.
            */
           if (noprobe) {
                   /* Read IIR a few times. */
                   for (fn = 0; fn < 2; fn ++) {
                           DELAY(10000);
                           failures[6] = sio_getreg(com, com_iir);
                   }
   
                   /* IIR_TXRDY should be clear.  Is it? */
                   result = 0;
                   if (failures[6] & IIR_TXRDY) {
                           /*
                            * No.  We seem to have the bug.  Does our fix for
                            * it work?
                            */
                           sio_setreg(com, com_ier, 0);
                           if (sio_getreg(com, com_iir) & IIR_NOPEND) {
                                   /* Yes.  We discovered the TXRDY bug! */
                                   SET_FLAG(dev, COM_C_IIR_TXRDYBUG);
                           } else {
                                   /* No.  Just fail.  XXX */
                                   result = ENXIO;
                                   sio_setreg(com, com_mcr, 0);
                           }
                   } else {
                           /* Yes.  No bug. */
                           CLR_FLAG(dev, COM_C_IIR_TXRDYBUG);
                   }
                   sio_setreg(com, com_ier, 0);
                   sio_setreg(com, com_cfcr, CFCR_8BITS);
                   mtx_unlock_spin(&sio_lock);
                   bus_release_resource(dev, SYS_RES_IOPORT, rid, port);
                   if (iobase == siocniobase)
                           result = 0;
                   if (result != 0) {
                           device_set_softc(dev, NULL);
                           free(com, M_DEVBUF);
                   }
                   return (result == 0 ? BUS_PROBE_DEFAULT + 1 : result);
           }
   
           /*
            * Check that
            *      o the CFCR, IER and MCR in UART hold the values written to them
            *        (the values happen to be all distinct - this is good for
            *        avoiding false positive tests from bus echoes).
            *      o an output interrupt is generated and its vector is correct.
            *      o the interrupt goes away when the IIR in the UART is read.
            */
   /* EXTRA DELAY? */
           failures[0] = sio_getreg(com, com_cfcr) - CFCR_8BITS;
           failures[1] = sio_getreg(com, com_ier) - IER_ETXRDY;
           failures[2] = sio_getreg(com, com_mcr) - mcr_image;
           DELAY(10000);           /* Some internal modems need this time */
           irqmap[1] = isa_irq_pending();
           failures[4] = (sio_getreg(com, com_iir) & IIR_IMASK) - IIR_TXRDY;
           DELAY(1000);            /* XXX */
           irqmap[2] = isa_irq_pending();
           failures[6] = (sio_getreg(com, com_iir) & IIR_IMASK) - IIR_NOPEND;
   
           /*
            * Turn off all device interrupts and check that they go off properly.
            * Leave MCR_IENABLE alone.  For ports without a master port, it gates
            * the OUT2 output of the UART to
            * the ICU input.  Closing the gate would give a floating ICU input
            * (unless there is another device driving it) and spurious interrupts.
            * (On the system that this was first tested on, the input floats high
            * and gives a (masked) interrupt as soon as the gate is closed.)
            */
           sio_setreg(com, com_ier, 0);
           sio_setreg(com, com_cfcr, CFCR_8BITS);  /* dummy to avoid bus echo */
           failures[7] = sio_getreg(com, com_ier);
           DELAY(1000);            /* XXX */
           irqmap[3] = isa_irq_pending();
           failures[9] = (sio_getreg(com, com_iir) & IIR_IMASK) - IIR_NOPEND;
   
           mtx_unlock_spin(&sio_lock);
   
           irqs = irqmap[1] & ~irqmap[0];
           if (bus_get_resource(idev, SYS_RES_IRQ, 0, &xirq, NULL) == 0 &&
               ((1 << xirq) & irqs) == 0) {
                   printf(
                   "sio%d: configured irq %ld not in bitmap of probed irqs %#x\n",
                       device_get_unit(dev), xirq, irqs);
                   printf(
                   "sio%d: port may not be enabled\n",
                       device_get_unit(dev));
           }
           if (bootverbose)
                   printf("sio%d: irq maps: %#x %#x %#x %#x\n",
                       device_get_unit(dev),
                       irqmap[0], irqmap[1], irqmap[2], irqmap[3]);
   
           result = 0;
           for (fn = 0; fn < sizeof failures; ++fn)
                   if (failures[fn]) {
                           sio_setreg(com, com_mcr, 0);
                           result = ENXIO;
                           if (bootverbose) {
                                   printf("sio%d: probe failed test(s):",
                                       device_get_unit(dev));
                                   for (fn = 0; fn < sizeof failures; ++fn)
                                           if (failures[fn])
                                                   printf(" %d", fn);
                                   printf("\n");
                           }
                           break;
                   }
           bus_release_resource(dev, SYS_RES_IOPORT, rid, port);
           if (iobase == siocniobase)
                   result = 0;
           if (result != 0) {
                   device_set_softc(dev, NULL);
                   free(com, M_DEVBUF);
           }
           return (result == 0 ? BUS_PROBE_DEFAULT + 1 : result);
   }
   
   #ifdef COM_ESP
   static int
   espattach(com, esp_port)
           struct com_s            *com;
           Port_t                  esp_port;
   {
           u_char  dips;
           u_char  val;
   
           /*
            * Check the ESP-specific I/O port to see if we're an ESP
            * card.  If not, return failure immediately.
            */
           if ((inb(esp_port) & 0xf3) == 0) {
                   printf(" port 0x%x is not an ESP board?\n", esp_port);
                   return (0);
           }
   
           /*
            * We've got something that claims to be a Hayes ESP card.
            * Let's hope so.
            */
   
           /* Get the dip-switch configuration */
           outb(esp_port + ESP_CMD1, ESP_GETDIPS);
           dips = inb(esp_port + ESP_STATUS1);
   
           /*
            * Bits 0,1 of dips say which COM port we are.
            */
           if (rman_get_start(com->ioportres) == likely_com_ports[dips & 0x03])
                   printf(" : ESP");
           else {
                   printf(" esp_port has com %d\n", dips & 0x03);
                   return (0);
           }
   
           /*
            * Check for ESP version 2.0 or later:  bits 4,5,6 = 010.
            */
           outb(esp_port + ESP_CMD1, ESP_GETTEST);
           val = inb(esp_port + ESP_STATUS1);      /* clear reg 1 */
           val = inb(esp_port + ESP_STATUS2);
           if ((val & 0x70) < 0x20) {
                   printf("-old (%o)", val & 0x70);
                   return (0);
           }
   
           /*
            * Check for ability to emulate 16550:  bit 7 == 1
            */
           if ((dips & 0x80) == 0) {
                   printf(" slave");
                   return (0);
           }
   
           /*
            * Okay, we seem to be a Hayes ESP card.  Whee.
            */
           com->esp = TRUE;
           com->esp_port = esp_port;
           return (1);
   }
   #endif /* COM_ESP */
   
   int
   sioattach(dev, xrid, rclk)
           device_t        dev;
           int             xrid;
           u_long          rclk;
   {
           struct com_s    *com;
   #ifdef COM_ESP
           Port_t          *espp;
   #endif
           Port_t          iobase;
           int             unit;
           u_int           flags;
           int             rid;
           struct resource *port;
           int             ret;
           int             error;
           struct tty      *tp;
   
           rid = xrid;
           port = bus_alloc_resource(dev, SYS_RES_IOPORT, &rid,
                                     0, ~0, IO_COMSIZE, RF_ACTIVE);
           if (!port)
                   return (ENXIO);
   
           iobase = rman_get_start(port);
           unit = device_get_unit(dev);
           com = device_get_softc(dev);
           flags = device_get_flags(dev);
   
           if (unit >= sio_numunits)
                   sio_numunits = unit + 1;
           /*
            * sioprobe() has initialized the device registers as follows:
            *      o cfcr = CFCR_8BITS.
            *        It is most important that CFCR_DLAB is off, so that the
            *        data port is not hidden when we enable interrupts.
            *      o ier = 0.
            *        Interrupts are only enabled when the line is open.
            *      o mcr = MCR_IENABLE, or 0 if the port has AST/4 compatible
            *        interrupt control register or the config specifies no irq.
            *        Keeping MCR_DTR and MCR_RTS off might stop the external
            *        device from sending before we are ready.
            */
           bzero(com, sizeof *com);
           com->unit = unit;
           com->ioportres = port;
           com->ioportrid = rid;
           com->bst = rman_get_bustag(port);
           com->bsh = rman_get_bushandle(port);
           com->cfcr_image = CFCR_8BITS;
           com->loses_outints = COM_LOSESOUTINTS(flags) != 0;
           com->no_irq = bus_get_resource(dev, SYS_RES_IRQ, 0, NULL, NULL) != 0;
           com->tx_fifo_size = 1;
           com->obufs[0].l_head = com->obuf1;
           com->obufs[1].l_head = com->obuf2;
   
           com->data_port = iobase + com_data;
           com->int_ctl_port = iobase + com_ier;
           com->int_id_port = iobase + com_iir;
           com->modem_ctl_port = iobase + com_mcr;
           com->mcr_image = inb(com->modem_ctl_port);
           com->line_status_port = iobase + com_lsr;
           com->modem_status_port = iobase + com_msr;
   
           tp = com->tp = ttyalloc();
           tp->t_oproc = comstart;
           tp->t_param = comparam;
           tp->t_stop = comstop;
           tp->t_modem = commodem;
           tp->t_break = combreak;
           tp->t_close = comclose;
           tp->t_open = comopen;
           tp->t_sc = com;
   
           if (rclk == 0)
                   rclk = DEFAULT_RCLK;
           com->rclk = rclk;
   
           if (unit == comconsole)
                   ttyconsolemode(tp, comdefaultrate);
           error = siosetwater(com, tp->t_init_in.c_ispeed);
           mtx_unlock_spin(&sio_lock);
           if (error) {
                   /*
                    * Leave i/o resources allocated if this is a `cn'-level
                    * console, so that other devices can't snarf them.
                    */
                   if (iobase != siocniobase)
                           bus_release_resource(dev, SYS_RES_IOPORT, rid, port);
                   return (ENOMEM);
           }
   
           /* attempt to determine UART type */
           printf("sio%d: type", unit);
   
           if (!COM_ISMULTIPORT(flags) &&
               !COM_IIR_TXRDYBUG(flags) && !COM_NOSCR(flags)) {
                   u_char  scr;
                   u_char  scr1;
                   u_char  scr2;
   
                   scr = sio_getreg(com, com_scr);
                   sio_setreg(com, com_scr, 0xa5);
                   scr1 = sio_getreg(com, com_scr);
                   sio_setreg(com, com_scr, 0x5a);
                   scr2 = sio_getreg(com, com_scr);
                   sio_setreg(com, com_scr, scr);
                   if (scr1 != 0xa5 || scr2 != 0x5a) {
                           printf(" 8250 or not responding");
                           goto determined_type;
                   }
           }
           sio_setreg(com, com_fifo, FIFO_ENABLE | FIFO_RX_HIGH);
           DELAY(100);
           switch (inb(com->int_id_port) & IIR_FIFO_MASK) {
           case FIFO_RX_LOW:
                   printf(" 16450");
                   break;
           case FIFO_RX_MEDL:
                   printf(" 16450?");
                   break;
           case FIFO_RX_MEDH:
                   printf(" 16550?");
                   break;
           case FIFO_RX_HIGH:
                   if (COM_NOFIFO(flags)) {
                           printf(" 16550A fifo disabled");
                           break;
                   }
                   com->hasfifo = TRUE;
                   if (COM_ST16650A(flags)) {
                           printf(" ST16650A");
                           com->st16650a = TRUE;
                           com->tx_fifo_size = 32;
                           break;
                   }
                   if (COM_TI16754(flags)) {
                           printf(" TI16754");
                           com->tx_fifo_size = 64;
                           break;
                   }
                   printf(" 16550A");
   #ifdef COM_ESP
                   for (espp = likely_esp_ports; *espp != 0; espp++)
                           if (espattach(com, *espp)) {
                                   com->tx_fifo_size = 1024;
                                   break;
                           }
                   if (com->esp)
                           break;
   #endif
                  com->tx_fifo_size = COM_FIFOSIZE(flags);
                  if (com->tx_fifo_size == 0)
                          com->tx_fifo_size = 16;
                  else
                          printf(" lookalike with %u bytes FIFO",
                                 com->tx_fifo_size);
                  break;
          }
  #ifdef COM_ESP
          if (com->esp) {
                  /*
                   * Set 16550 compatibility mode.
                   * We don't use the ESP_MODE_SCALE bit to increase the
                   * fifo trigger levels because we can't handle large
                   * bursts of input.
                   * XXX flow control should be set in comparam(), not here.
                   */
                  outb(com->esp_port + ESP_CMD1, ESP_SETMODE);
                  outb(com->esp_port + ESP_CMD2, ESP_MODE_RTS | ESP_MODE_FIFO);
  
                  /* Set RTS/CTS flow control. */
                  outb(com->esp_port + ESP_CMD1, ESP_SETFLOWTYPE);
                  outb(com->esp_port + ESP_CMD2, ESP_FLOW_RTS);
                  outb(com->esp_port + ESP_CMD2, ESP_FLOW_CTS);
  
                  /* Set flow-control levels. */
                  outb(com->esp_port + ESP_CMD1, ESP_SETRXFLOW);
                  outb(com->esp_port + ESP_CMD2, HIBYTE(768));
                  outb(com->esp_port + ESP_CMD2, LOBYTE(768));
                  outb(com->esp_port + ESP_CMD2, HIBYTE(512));
                  outb(com->esp_port + ESP_CMD2, LOBYTE(512));
          }
  #endif /* COM_ESP */
          sio_setreg(com, com_fifo, 0);
  determined_type: ;
  
  #ifdef COM_MULTIPORT
          if (COM_ISMULTIPORT(flags)) {
                  device_t masterdev;
  
                  com->multiport = TRUE;
                  printf(" (multiport");
                  if (unit == COM_MPMASTER(flags))
                          printf(" master");
                  printf(")");
                  masterdev = devclass_get_device(sio_devclass,
                      COM_MPMASTER(flags));
                  com->no_irq = (masterdev == NULL || bus_get_resource(masterdev,
                      SYS_RES_IRQ, 0, NULL, NULL) != 0);
           }
  #endif /* COM_MULTIPORT */
          if (unit == comconsole)
                  printf(", console");
          if (COM_IIR_TXRDYBUG(flags))
                  printf(" with a buggy IIR_TXRDY implementation");
          printf("\n");
  
          if (sio_fast_ih == NULL) {
                  swi_add(&tty_intr_event, "sio", siopoll, NULL, SWI_TTY, 0,
                      &sio_fast_ih);
                  swi_add(&clk_intr_event, "sio", siopoll, NULL, SWI_CLOCK, 0,
                      &sio_slow_ih);
          }
  
          com->flags = flags;
          com->pps.ppscap = PPS_CAPTUREASSERT | PPS_CAPTURECLEAR;
          tp->t_pps = &com->pps;
  
          if (COM_PPSCTS(flags))
                  com->pps_bit = MSR_CTS;
          else
                  com->pps_bit = MSR_DCD;
          pps_init(&com->pps);
  
          rid = 0;
          com->irqres = bus_alloc_resource_any(dev, SYS_RES_IRQ, &rid, RF_ACTIVE);
          if (com->irqres) {
                  ret = bus_setup_intr(dev, com->irqres,
                                       INTR_TYPE_TTY,
                                       siointr, NULL, com, 
                                       &com->cookie);
                  if (ret) {
                          ret = bus_setup_intr(dev,
                                               com->irqres, INTR_TYPE_TTY,
                                               NULL, (driver_intr_t *)siointr, com, &com->cookie);
                          if (ret == 0)
                                  device_printf(dev, "unable to activate interrupt in fast mode - using normal mode\n");
                  }
                  if (ret)
                          device_printf(dev, "could not activate interrupt\n");
  #if defined(KDB) && (defined(BREAK_TO_DEBUGGER) || \
      defined(ALT_BREAK_TO_DEBUGGER))
                  /*
                   * Enable interrupts for early break-to-debugger support
                   * on the console.
                   */
                  if (ret == 0 && unit == comconsole)
                          outb(siocniobase + com_ier, IER_ERXRDY | IER_ERLS |
                              IER_EMSC);
  #endif
          }
  
          /* We're ready, open the doors... */
          ttycreate(tp, TS_CALLOUT, "d%r", unit);
  
          return (0);
  }
  
  static int
  comopen(struct tty *tp, struct cdev *dev)
  {
          struct com_s    *com;
          int i;
  
          com = tp->t_sc;
          com->poll = com->no_irq;
          com->poll_output = com->loses_outints;
          if (com->hasfifo) {
                  /*
                   * (Re)enable and drain fifos.
                   *
                   * Certain SMC chips cause problems if the fifos
                   * are enabled while input is ready.  Turn off the
                   * fifo if necessary to clear the input.  We test
                   * the input ready bit after enabling the fifos
                   * since we've already enabled them in comparam()
                   * and to handle races between enabling and fresh
                   * input.
                   */
                  for (i = 0; i < 500; i++) {
                          sio_setreg(com, com_fifo,
                                     FIFO_RCV_RST | FIFO_XMT_RST
                                     | com->fifo_image);
                          /*
                           * XXX the delays are for superstitious
                           * historical reasons.  It must be less than
                           * the character time at the maximum
                           * supported speed (87 usec at 115200 bps
                           * 8N1).  Otherwise we might loop endlessly
                           * if data is streaming in.  We used to use
                           * delays of 100.  That usually worked
                           * because DELAY(100) used to usually delay
                           * for about 85 usec instead of 100.
                           */
                          DELAY(50);
                          if (!(inb(com->line_status_port) & LSR_RXRDY))
                                  break;
                          sio_setreg(com, com_fifo, 0);
                          DELAY(50);
                          (void) inb(com->data_port);
                  }
                  if (i == 500)
                          return (EIO);
          }
  
          mtx_lock_spin(&sio_lock);
          (void) inb(com->line_status_port);
          (void) inb(com->data_port);
          com->prev_modem_status = com->last_modem_status
              = inb(com->modem_status_port);
          outb(com->int_ctl_port,
               IER_ERXRDY | IER_ERLS | IER_EMSC
               | (COM_IIR_TXRDYBUG(com->flags) ? 0 : IER_ETXRDY));
          mtx_unlock_spin(&sio_lock);
          siosettimeout();
          /* XXX: should be generic ? */
          if (com->prev_modem_status & MSR_DCD || ISCALLOUT(dev))
                  ttyld_modem(tp, 1);
          return (0);
  }
  
  static void
  comclose(tp)
          struct tty      *tp;
  {
          int             s;
          struct com_s    *com;
  
          s = spltty();
          com = tp->t_sc;
          com->poll = FALSE;
          com->poll_output = FALSE;
          sio_setreg(com, com_cfcr, com->cfcr_image &= ~CFCR_SBREAK);
  
  #if defined(KDB) && (defined(BREAK_TO_DEBUGGER) || \
      defined(ALT_BREAK_TO_DEBUGGER))
          /*
           * Leave interrupts enabled and don't clear DTR if this is the
           * console. This allows us to detect break-to-debugger events
           * while the console device is closed.
           */
          if (com->unit != comconsole)
  #endif
          {
                  sio_setreg(com, com_ier, 0);
                  if (tp->t_cflag & HUPCL
                      /*
                       * XXX we will miss any carrier drop between here and the
                       * next open.  Perhaps we should watch DCD even when the
                       * port is closed; it is not sufficient to check it at
                       * the next open because it might go up and down while
                       * we're not watching.
                       */
                      || (!tp->t_actout
                          && !(com->prev_modem_status & MSR_DCD)
                          && !(tp->t_init_in.c_cflag & CLOCAL))
                      || !(tp->t_state & TS_ISOPEN)) {
                          (void)commodem(tp, 0, SER_DTR);
                          ttydtrwaitstart(tp);
                  }
          }
          if (com->hasfifo) {
                  /*
                   * Disable fifos so that they are off after controlled
                   * reboots.  Some BIOSes fail to detect 16550s when the
                   * fifos are enabled.
                   */
                  sio_setreg(com, com_fifo, 0);
          }
          tp->t_actout = FALSE;
          wakeup(&tp->t_actout);
          wakeup(TSA_CARR_ON(tp));        /* restart any wopeners */
          siosettimeout();
          splx(s);
  }
  
  static void
  siobusycheck(chan)
          void    *chan;
  {
          struct com_s    *com;
          int             s;
  
          com = (struct com_s *)chan;
  
          /*
           * Clear TS_BUSY if low-level output is complete.
           * spl locking is sufficient because siointr1() does not set CS_BUSY.
           * If siointr1() clears CS_BUSY after we look at it, then we'll get
           * called again.  Reading the line status port outside of siointr1()
           * is safe because CS_BUSY is clear so there are no output interrupts
           * to lose.
           */
          s = spltty();
          if (com->state & CS_BUSY)
                  com->extra_state &= ~CSE_BUSYCHECK;     /* False alarm. */
          else if ((inb(com->line_status_port) & (LSR_TSRE | LSR_TXRDY))
              == (LSR_TSRE | LSR_TXRDY)) {
                  com->tp->t_state &= ~TS_BUSY;
                  ttwwakeup(com->tp);
                  com->extra_state &= ~CSE_BUSYCHECK;
          } else
                  timeout(siobusycheck, com, hz / 100);
          splx(s);
  }
  
  static u_int
  siodivisor(rclk, speed)
          u_long  rclk;
          speed_t speed;
  {
          long    actual_speed;
          u_int   divisor;
          int     error;
  
          if (speed == 0)
                  return (0);
  #if UINT_MAX > (ULONG_MAX - 1) / 8
          if (speed > (ULONG_MAX - 1) / 8)
                  return (0);
  #endif
          divisor = (rclk / (8UL * speed) + 1) / 2;
          if (divisor == 0 || divisor >= 65536)
                  return (0);
          actual_speed = rclk / (16UL * divisor);
  
          /* 10 times error in percent: */
          error = ((actual_speed - (long)speed) * 2000 / (long)speed + 1) / 2;
  
          /* 3.0% maximum error tolerance: */
          if (error < -30 || error > 30)
                  return (0);
  
          return (divisor);
  }
  
  /*
   * Call this function with the sio_lock mutex held.  It will return with the
   * lock still held.
   */
  static void
  sioinput(com)
          struct com_s    *com;
  {
          u_char          *buf;
          int             incc;
          u_char          line_status;
          int             recv_data;
          struct tty      *tp;
  
          buf = com->ibuf;
          tp = com->tp;
          if (!(tp->t_state & TS_ISOPEN) || !(tp->t_cflag & CREAD)) {
                  com_events -= (com->iptr - com->ibuf);
                  com->iptr = com->ibuf;
                  return;
          }
          if (tp->t_state & TS_CAN_BYPASS_L_RINT) {
                  /*
                   * Avoid the grotesquely inefficient lineswitch routine
                   * (ttyinput) in "raw" mode.  It usually takes about 450
                   * instructions (that's without canonical processing or echo!).
                   * slinput is reasonably fast (usually 40 instructions plus
                   * call overhead).
                   */
                  do {
                          /*
                           * This may look odd, but it is using save-and-enable
                           * semantics instead of the save-and-disable semantics
                           * that are used everywhere else.
                           */
                          mtx_unlock_spin(&sio_lock);
                          incc = com->iptr - buf;
                          if (tp->t_rawq.c_cc + incc > tp->t_ihiwat
                              && (com->state & CS_RTS_IFLOW
                                  || tp->t_iflag & IXOFF)
                              && !(tp->t_state & TS_TBLOCK))
                                  ttyblock(tp);
                          com->delta_error_counts[CE_TTY_BUF_OVERFLOW]
                                  += b_to_q((char *)buf, incc, &tp->t_rawq);
                          buf += incc;
                          tk_nin += incc;
                          tk_rawcc += incc;
                          tp->t_rawcc += incc;
                          ttwakeup(tp);
                          if (tp->t_state & TS_TTSTOP
                              && (tp->t_iflag & IXANY
                                  || tp->t_cc[VSTART] == tp->t_cc[VSTOP])) {
                                  tp->t_state &= ~TS_TTSTOP;
                                  tp->t_lflag &= ~FLUSHO;
                                  comstart(tp);
                          }
                          mtx_lock_spin(&sio_lock);
                  } while (buf < com->iptr);
          } else {
                  do {
                          /*
                           * This may look odd, but it is using save-and-enable
                           * semantics instead of the save-and-disable semantics
                           * that are used everywhere else.
                           */
                          mtx_unlock_spin(&sio_lock);
                          line_status = buf[com->ierroff];
                          recv_data = *buf++;
                          if (line_status
                              & (LSR_BI | LSR_FE | LSR_OE | LSR_PE)) {
                                  if (line_status & LSR_BI)
                                          recv_data |= TTY_BI;
                                  if (line_status & LSR_FE)
                                          recv_data |= TTY_FE;
                                  if (line_status & LSR_OE)
                                          recv_data |= TTY_OE;
                                  if (line_status & LSR_PE)
                                          recv_data |= TTY_PE;
                          }
                          ttyld_rint(tp, recv_data);
                          mtx_lock_spin(&sio_lock);
                  } while (buf < com->iptr);
          }
          com_events -= (com->iptr - com->ibuf);
          com->iptr = com->ibuf;
  
          /*
           * There is now room for another low-level buffer full of input,
           * so enable RTS if it is now disabled and there is room in the
           * high-level buffer.
           */
          if ((com->state & CS_RTS_IFLOW) && !(com->mcr_image & MCR_RTS) &&
              !(tp->t_state & TS_TBLOCK))
                  outb(com->modem_ctl_port, com->mcr_image |= MCR_RTS);
  }
  
  static int
  siointr(arg)
          void            *arg;
  {
          struct com_s    *com;
  
  #ifndef COM_MULTIPORT
          com = (struct com_s *)arg;
  
          mtx_lock_spin(&sio_lock);
          siointr1(com);
          mtx_unlock_spin(&sio_lock);
  #else /* COM_MULTIPORT */
          bool_t          possibly_more_intrs;
          int             unit;
  
          /*
           * Loop until there is no activity on any port.  This is necessary
           * to get an interrupt edge more than to avoid another interrupt.
           * If the IRQ signal is just an OR of the IRQ signals from several
           * devices, then the edge from one may be lost because another is
           * on.
           */
          mtx_lock_spin(&sio_lock);
          do {
                  possibly_more_intrs = FALSE;
                  for (unit = 0; unit < sio_numunits; ++unit) {
                          com = com_addr(unit);
                          /*
                           * XXX COM_LOCK();
                           * would it work here, or be counter-productive?
                           */
                          if (com != NULL 
                              && !com->gone
                              && (inb(com->int_id_port) & IIR_IMASK)
                                 != IIR_NOPEND) {
                                  siointr1(com);
                                  possibly_more_intrs = TRUE;
                          }
                          /* XXX COM_UNLOCK(); */
                  }
          } while (possibly_more_intrs);
          mtx_unlock_spin(&sio_lock);
  #endif /* COM_MULTIPORT */
          return(FILTER_HANDLED);
  }
  
  static struct timespec siots[8];
  static int siotso;
  static int volatile siotsunit = -1;
  
  static int
  sysctl_siots(SYSCTL_HANDLER_ARGS)
  {
          char buf[128];
          long long delta;
          size_t len;
          int error, i, tso;
  
          for (i = 1, tso = siotso; i < tso; i++) {
                  delta = (long long)(siots[i].tv_sec - siots[i - 1].tv_sec) *
                      1000000000 +
                      (siots[i].tv_nsec - siots[i - 1].tv_nsec);
                  len = sprintf(buf, "%lld\n", delta);
                  if (delta >= 110000)
                          len += sprintf(buf + len - 1, ": *** %ld.%09ld\n",
                              (long)siots[i].tv_sec, siots[i].tv_nsec) - 1;
                  if (i == tso - 1)
                          buf[len - 1] = '\0';
                  error = SYSCTL_OUT(req, buf, len);
                  if (error != 0)
                          return (error);
                  uio_yield();
          }
          return (0);
  }
  
  SYSCTL_PROC(_machdep, OID_AUTO, siots, CTLTYPE_STRING | CTLFLAG_RD,
      0, 0, sysctl_siots, "A", "sio timestamps");
  
  static void
  siointr1(com)
          struct com_s    *com;
  {
          u_char  int_ctl;
          u_char  int_ctl_new;
          u_char  line_status;
          u_char  modem_status;
          u_char  *ioptr;
          u_char  recv_data;
  
          if (COM_IIR_TXRDYBUG(com->flags)) {
                  int_ctl = inb(com->int_ctl_port);
                  int_ctl_new = int_ctl;
          } else {
                  int_ctl = 0;
                  int_ctl_new = 0;
          }
  
          while (!com->gone) {
                  if (com->pps.ppsparam.mode & PPS_CAPTUREBOTH) {
                          modem_status = inb(com->modem_status_port);
                          if ((modem_status ^ com->last_modem_status) &
                              com->pps_bit) {
                                  pps_capture(&com->pps);
                                  pps_event(&com->pps,
                                      (modem_status & com->pps_bit) ? 
                                      PPS_CAPTUREASSERT : PPS_CAPTURECLEAR);
                          }
                  }
                  line_status = inb(com->line_status_port);
  
                  /* input event? (check first to help avoid overruns) */
                  while (line_status & LSR_RCV_MASK) {
                          /* break/unnattached error bits or real input? */
                          if (!(line_status & LSR_RXRDY))
                                  recv_data = 0;
                          else
                                  recv_data = inb(com->data_port);
  #ifdef KDB
  #ifdef ALT_BREAK_TO_DEBUGGER
                          if (com->unit == comconsole &&
                              kdb_alt_break(recv_data, &com->alt_brk_state) != 0)
                                  kdb_enter_why(KDB_WHY_BREAK,
                                      "Break sequence on console");
  #endif /* ALT_BREAK_TO_DEBUGGER */
  #endif /* KDB */
                          if (line_status & (LSR_BI | LSR_FE | LSR_PE)) {
                                  /*
                                   * Don't store BI if IGNBRK or FE/PE if IGNPAR.
                                   * Otherwise, push the work to a higher level
                                   * (to handle PARMRK) if we're bypassing.
                                   * Otherwise, convert BI/FE and PE+INPCK to 0.
                                   *
                                   * This makes bypassing work right in the
                                   * usual "raw" case (IGNBRK set, and IGNPAR
                                   * and INPCK clear).
                                   *
                                   * Note: BI together with FE/PE means just BI.
                                   */
                                  if (line_status & LSR_BI) {
  #if defined(KDB) && defined(BREAK_TO_DEBUGGER)
                                          if (com->unit == comconsole) {
                                                  kdb_enter_why(KDB_WHY_BREAK,
                                                      "Line break on console");
                                                  goto cont;
                                          }
  #endif
                                          if (com->tp == NULL
                                              || com->tp->t_iflag & IGNBRK)
                                                  goto cont;
                                  } else {
                                          if (com->tp == NULL
                                              || com->tp->t_iflag & IGNPAR)
                                                  goto cont;
                                  }
                                  if (com->tp->t_state & TS_CAN_BYPASS_L_RINT
                                      && (line_status & (LSR_BI | LSR_FE)
                                          || com->tp->t_iflag & INPCK))
                                          recv_data = 0;
                          }
                          ++com->bytes_in;
                          if (com->tp != NULL &&
                              com->tp->t_hotchar != 0 && recv_data == com->tp->t_hotchar)
                                  swi_sched(sio_fast_ih, 0);
                          ioptr = com->iptr;
                          if (ioptr >= com->ibufend)
                                  CE_RECORD(com, CE_INTERRUPT_BUF_OVERFLOW);
                          else {
                                  if (com->tp != NULL && com->tp->t_do_timestamp)
                                          microtime(&com->tp->t_timestamp);
                                  ++com_events;
                                  swi_sched(sio_slow_ih, SWI_DELAY);
  #if 0 /* for testing input latency vs efficiency */
  if (com->iptr - com->ibuf == 8)
          swi_sched(sio_fast_ih, 0);
  #endif
                                  ioptr[0] = recv_data;
                                  ioptr[com->ierroff] = line_status;
                                  com->iptr = ++ioptr;
                                  if (ioptr == com->ihighwater
                                      && com->state & CS_RTS_IFLOW)
                                          outb(com->modem_ctl_port,
                                               com->mcr_image &= ~MCR_RTS);
                                  if (line_status & LSR_OE)
                                          CE_RECORD(com, CE_OVERRUN);
                          }
  cont:
                          if (line_status & LSR_TXRDY
                              && com->state >= (CS_BUSY | CS_TTGO | CS_ODEVREADY))
                                  goto txrdy;
  
                          /*
                           * "& 0x7F" is to avoid the gcc-1.40 generating a slow
                           * jump from the top of the loop to here
                           */
                          line_status = inb(com->line_status_port) & 0x7F;
                  }
  
                  /* modem status change? (always check before doing output) */
                  modem_status = inb(com->modem_status_port);
                  if (modem_status != com->last_modem_status) {
                          /*
                           * Schedule high level to handle DCD changes.  Note
                           * that we don't use the delta bits anywhere.  Some
                           * UARTs mess them up, and it's easy to remember the
                           * previous bits and calculate the delta.
                           */
                          com->last_modem_status = modem_status;
                          if (!(com->state & CS_CHECKMSR)) {
                                  com_events += LOTS_OF_EVENTS;
                                  com->state |= CS_CHECKMSR;
                                  swi_sched(sio_fast_ih, 0);
                          }
  
                          /* handle CTS change immediately for crisp flow ctl */
                          if (com->state & CS_CTS_OFLOW) {
                                  if (modem_status & MSR_CTS)
                                          com->state |= CS_ODEVREADY;
                                  else
                                          com->state &= ~CS_ODEVREADY;
                          }
                  }
  
  txrdy:
                  /* output queued and everything ready? */
                  if (line_status & LSR_TXRDY
                      && com->state >= (CS_BUSY | CS_TTGO | CS_ODEVREADY)) {
                          ioptr = com->obufq.l_head;
                          if (com->tx_fifo_size > 1 && com->unit != siotsunit) {
                                  u_int   ocount;
  
                                  ocount = com->obufq.l_tail - ioptr;
                                  if (ocount > com->tx_fifo_size)
                                          ocount = com->tx_fifo_size;
                                  com->bytes_out += ocount;
                                  do
                                          outb(com->data_port, *ioptr++);
                                  while (--ocount != 0);
                          } else {
                                  outb(com->data_port, *ioptr++);
                                  ++com->bytes_out;
                                  if (com->unit == siotsunit
                                      && siotso < sizeof siots / sizeof siots[0])
                                          nanouptime(&siots[siotso++]);
                          }
                          com->obufq.l_head = ioptr;
                          if (COM_IIR_TXRDYBUG(com->flags))
                                  int_ctl_new = int_ctl | IER_ETXRDY;
                          if (ioptr >= com->obufq.l_tail) {
                                  struct lbq      *qp;
  
                                  qp = com->obufq.l_next;
                                  qp->l_queued = FALSE;
                                  qp = qp->l_next;
                                  if (qp != NULL) {
                                          com->obufq.l_head = qp->l_head;
                                          com->obufq.l_tail = qp->l_tail;
                                          com->obufq.l_next = qp;
                                  } else {
                                          /* output just completed */
                                          if (COM_IIR_TXRDYBUG(com->flags))
                                                  int_ctl_new = int_ctl
                                                                & ~IER_ETXRDY;
                                          com->state &= ~CS_BUSY;
                                  }
                                  if (!(com->state & CS_ODONE)) {
                                          com_events += LOTS_OF_EVENTS;
                                          com->state |= CS_ODONE;
                                          /* handle at high level ASAP */
                                          swi_sched(sio_fast_ih, 0);
                                  }
                          }
                          if (COM_IIR_TXRDYBUG(com->flags)
                              && int_ctl != int_ctl_new)
                                  outb(com->int_ctl_port, int_ctl_new);
                  }
  
                  /* finished? */
  #ifndef COM_MULTIPORT
                  if ((inb(com->int_id_port) & IIR_IMASK) == IIR_NOPEND)
  #endif /* COM_MULTIPORT */
                          return;
          }
  }
  
  /* software interrupt handler for SWI_TTY */
  static void
  siopoll(void *dummy)
  {
          int             unit;
  
          if (com_events == 0)
                  return;
  repeat:
          for (unit = 0; unit < sio_numunits; ++unit) {
                  struct com_s    *com;
                  int             incc;
                  struct tty      *tp;
  
                  com = com_addr(unit);
                  if (com == NULL)
                          continue;
                  tp = com->tp;
                  if (tp == NULL || com->gone) {
                          /*
                           * Discard any events related to never-opened or
                           * going-away devices.
                           */
                          mtx_lock_spin(&sio_lock);
                          incc = com->iptr - com->ibuf;
                          com->iptr = com->ibuf;
                          if (com->state & CS_CHECKMSR) {
                                  incc += LOTS_OF_EVENTS;
                                  com->state &= ~CS_CHECKMSR;
                          }
                          com_events -= incc;
                          mtx_unlock_spin(&sio_lock);
                          continue;
                  }
                  if (com->iptr != com->ibuf) {
                          mtx_lock_spin(&sio_lock);
                          sioinput(com);
                          mtx_unlock_spin(&sio_lock);
                  }
                  if (com->state & CS_CHECKMSR) {
                          u_char  delta_modem_status;
  
                          mtx_lock_spin(&sio_lock);
                          delta_modem_status = com->last_modem_status
                                               ^ com->prev_modem_status;
                          com->prev_modem_status = com->last_modem_status;
                          com_events -= LOTS_OF_EVENTS;
                          com->state &= ~CS_CHECKMSR;
                          mtx_unlock_spin(&sio_lock);
                          if (delta_modem_status & MSR_DCD)
                                  ttyld_modem(tp,
                                      com->prev_modem_status & MSR_DCD);
                  }
                  if (com->state & CS_ODONE) {
                          mtx_lock_spin(&sio_lock);
                          com_events -= LOTS_OF_EVENTS;
                          com->state &= ~CS_ODONE;
                          mtx_unlock_spin(&sio_lock);
                          if (!(com->state & CS_BUSY)
                              && !(com->extra_state & CSE_BUSYCHECK)) {
                                  timeout(siobusycheck, com, hz / 100);
                                  com->extra_state |= CSE_BUSYCHECK;
                          }
                          ttyld_start(tp);
                  }
                  if (com_events == 0)
                          break;
          }
          if (com_events >= LOTS_OF_EVENTS)
                  goto repeat;
  }
  
  static void
  combreak(tp, sig)
          struct tty      *tp;
          int             sig;
  {
          struct com_s    *com;
  
          com = tp->t_sc;
  
          if (sig)
                  sio_setreg(com, com_cfcr, com->cfcr_image |= CFCR_SBREAK);
          else
                  sio_setreg(com, com_cfcr, com->cfcr_image &= ~CFCR_SBREAK);
  }
  
  static int
  comparam(tp, t)
          struct tty      *tp;
          struct termios  *t;
  {
          u_int           cfcr;
          int             cflag;
          struct com_s    *com;
          u_int           divisor;
          u_char          dlbh;
          u_char          dlbl;
          u_char          efr_flowbits;
          int             s;
  
          com = tp->t_sc;
          if (com == NULL)
                  return (ENODEV);
  
          /* check requested parameters */
          if (t->c_ispeed != (t->c_ospeed != 0 ? t->c_ospeed : tp->t_ospeed))
                  return (EINVAL);
          divisor = siodivisor(com->rclk, t->c_ispeed);
          if (divisor == 0)
                  return (EINVAL);
  
          /* parameters are OK, convert them to the com struct and the device */
          s = spltty();
          if (t->c_ospeed == 0)
                  (void)commodem(tp, 0, SER_DTR); /* hang up line */
          else
                  (void)commodem(tp, SER_DTR, 0);
          cflag = t->c_cflag;
          switch (cflag & CSIZE) {
          case CS5:
                  cfcr = CFCR_5BITS;
                  break;
          case CS6:
                  cfcr = CFCR_6BITS;
                  break;
          case CS7:
                  cfcr = CFCR_7BITS;
                  break;
          default:
                  cfcr = CFCR_8BITS;
                  break;
          }
          if (cflag & PARENB) {
                  cfcr |= CFCR_PENAB;
                  if (!(cflag & PARODD))
                          cfcr |= CFCR_PEVEN;
          }
          if (cflag & CSTOPB)
                  cfcr |= CFCR_STOPB;
  
          if (com->hasfifo) {
                  /*
                   * Use a fifo trigger level low enough so that the input
                   * latency from the fifo is less than about 16 msec and
                   * the total latency is less than about 30 msec.  These
                   * latencies are reasonable for humans.  Serial comms
                   * protocols shouldn't expect anything better since modem
                   * latencies are larger.
                   *
                   * The fifo trigger level cannot be set at RX_HIGH for high
                   * speed connections without further work on reducing 
                   * interrupt disablement times in other parts of the system,
                   * without producing silo overflow errors.
                   */
                  com->fifo_image = com->unit == siotsunit ? 0
                                    : t->c_ispeed <= 4800
                                    ? FIFO_ENABLE : FIFO_ENABLE | FIFO_RX_MEDH;
  #ifdef COM_ESP
                  /*
                   * The Hayes ESP card needs the fifo DMA mode bit set
                   * in compatibility mode.  If not, it will interrupt
                   * for each character received.
                   */
                  if (com->esp)
                          com->fifo_image |= FIFO_DMA_MODE;
  #endif
                  sio_setreg(com, com_fifo, com->fifo_image);
          }
  
          /*
           * This returns with interrupts disabled so that we can complete
           * the speed change atomically.  Keeping interrupts disabled is
           * especially important while com_data is hidden.
           */
          (void) siosetwater(com, t->c_ispeed);
  
          sio_setreg(com, com_cfcr, cfcr | CFCR_DLAB);
          /*
           * Only set the divisor registers if they would change, since on
           * some 16550 incompatibles (UMC8669F), setting them while input
           * is arriving loses sync until data stops arriving.
           */
          dlbl = divisor & 0xFF;
          if (sio_getreg(com, com_dlbl) != dlbl)
                  sio_setreg(com, com_dlbl, dlbl);
          dlbh = divisor >> 8;
          if (sio_getreg(com, com_dlbh) != dlbh)
                  sio_setreg(com, com_dlbh, dlbh);
  
          efr_flowbits = 0;
  
          if (cflag & CRTS_IFLOW) {
                  com->state |= CS_RTS_IFLOW;
                  efr_flowbits |= EFR_AUTORTS;
                  /*
                   * If CS_RTS_IFLOW just changed from off to on, the change
                   * needs to be propagated to MCR_RTS.  This isn't urgent,
                   * so do it later by calling comstart() instead of repeating
                   * a lot of code from comstart() here.
                   */
          } else if (com->state & CS_RTS_IFLOW) {
                  com->state &= ~CS_RTS_IFLOW;
                  /*
                   * CS_RTS_IFLOW just changed from on to off.  Force MCR_RTS
                   * on here, since comstart() won't do it later.
                   */
                  outb(com->modem_ctl_port, com->mcr_image |= MCR_RTS);
          }
  
          /*
           * Set up state to handle output flow control.
           * XXX - worth handling MDMBUF (DCD) flow control at the lowest level?
           * Now has 10+ msec latency, while CTS flow has 50- usec latency.
           */
          com->state |= CS_ODEVREADY;
          com->state &= ~CS_CTS_OFLOW;
          if (cflag & CCTS_OFLOW) {
                  com->state |= CS_CTS_OFLOW;
                  efr_flowbits |= EFR_AUTOCTS;
                  if (!(com->last_modem_status & MSR_CTS))
                          com->state &= ~CS_ODEVREADY;
          }
  
          if (com->st16650a) {
                  sio_setreg(com, com_lcr, LCR_EFR_ENABLE);
                  sio_setreg(com, com_efr,
                             (sio_getreg(com, com_efr)
                              & ~(EFR_AUTOCTS | EFR_AUTORTS)) | efr_flowbits);
          }
          sio_setreg(com, com_cfcr, com->cfcr_image = cfcr);
  
          /* XXX shouldn't call functions while intrs are disabled. */
          ttyldoptim(tp);
  
          mtx_unlock_spin(&sio_lock);
          splx(s);
          comstart(tp);
          if (com->ibufold != NULL) {
                  free(com->ibufold, M_DEVBUF);
                  com->ibufold = NULL;
          }
          return (0);
  }
  
  /*
   * This function must be called with the sio_lock mutex released and will
   * return with it obtained.
   */
  static int
  siosetwater(com, speed)
          struct com_s    *com;
          speed_t         speed;
  {
          int             cp4ticks;
          u_char          *ibuf;
          int             ibufsize;
          struct tty      *tp;
  
          /*
           * Make the buffer size large enough to handle a softtty interrupt
           * latency of about 2 ticks without loss of throughput or data
           * (about 3 ticks if input flow control is not used or not honoured,
           * but a bit less for CS5-CS7 modes).
           */
          cp4ticks = speed / 10 / hz * 4;
          for (ibufsize = 128; ibufsize < cp4ticks;)
                  ibufsize <<= 1;
          if (ibufsize == com->ibufsize) {
                  mtx_lock_spin(&sio_lock);
                  return (0);
          }
  
          /*
           * Allocate input buffer.  The extra factor of 2 in the size is
           * to allow for an error byte for each input byte.
           */
          ibuf = malloc(2 * ibufsize, M_DEVBUF, M_NOWAIT);
          if (ibuf == NULL) {
                  mtx_lock_spin(&sio_lock);
                  return (ENOMEM);
          }
  
          /* Initialize non-critical variables. */
          com->ibufold = com->ibuf;
          com->ibufsize = ibufsize;
          tp = com->tp;
          if (tp != NULL) {
                  tp->t_ififosize = 2 * ibufsize;
                  tp->t_ispeedwat = (speed_t)-1;
                  tp->t_ospeedwat = (speed_t)-1;
          }
  
          /*
           * Read current input buffer, if any.  Continue with interrupts
           * disabled.
           */
          mtx_lock_spin(&sio_lock);
          if (com->iptr != com->ibuf)
                  sioinput(com);
  
          /*-
           * Initialize critical variables, including input buffer watermarks.
           * The external device is asked to stop sending when the buffer
           * exactly reaches high water, or when the high level requests it.
           * The high level is notified immediately (rather than at a later
           * clock tick) when this watermark is reached.
           * The buffer size is chosen so the watermark should almost never
           * be reached.
           * The low watermark is invisibly 0 since the buffer is always
           * emptied all at once.
           */
          com->iptr = com->ibuf = ibuf;
          com->ibufend = ibuf + ibufsize;
          com->ierroff = ibufsize;
          com->ihighwater = ibuf + 3 * ibufsize / 4;
          return (0);
  }
  
  static void
  comstart(tp)
          struct tty      *tp;
  {
          struct com_s    *com;
          int             s;
  
          com = tp->t_sc;
          if (com == NULL)
                  return;
          s = spltty();
          mtx_lock_spin(&sio_lock);
          if (tp->t_state & TS_TTSTOP)
                  com->state &= ~CS_TTGO;
          else
                  com->state |= CS_TTGO;
          if (tp->t_state & TS_TBLOCK) {
                  if (com->mcr_image & MCR_RTS && com->state & CS_RTS_IFLOW)
                          outb(com->modem_ctl_port, com->mcr_image &= ~MCR_RTS);
          } else {
                  if (!(com->mcr_image & MCR_RTS) && com->iptr < com->ihighwater
                      && com->state & CS_RTS_IFLOW)
                          outb(com->modem_ctl_port, com->mcr_image |= MCR_RTS);
          }
          mtx_unlock_spin(&sio_lock);
          if (tp->t_state & (TS_TIMEOUT | TS_TTSTOP)) {
                  ttwwakeup(tp);
                  splx(s);
                  return;
          }
          if (tp->t_outq.c_cc != 0) {
                  struct lbq      *qp;
                  struct lbq      *next;
  
                  if (!com->obufs[0].l_queued) {
                          com->obufs[0].l_tail
                              = com->obuf1 + q_to_b(&tp->t_outq, com->obuf1,
                                                    sizeof com->obuf1);
                          com->obufs[0].l_next = NULL;
                          com->obufs[0].l_queued = TRUE;
                          mtx_lock_spin(&sio_lock);
                          if (com->state & CS_BUSY) {
                                  qp = com->obufq.l_next;
                                  while ((next = qp->l_next) != NULL)
                                          qp = next;
                                  qp->l_next = &com->obufs[0];
                          } else {
                                  com->obufq.l_head = com->obufs[0].l_head;
                                  com->obufq.l_tail = com->obufs[0].l_tail;
                                  com->obufq.l_next = &com->obufs[0];
                                  com->state |= CS_BUSY;
                          }
                          mtx_unlock_spin(&sio_lock);
                  }
                  if (tp->t_outq.c_cc != 0 && !com->obufs[1].l_queued) {
                          com->obufs[1].l_tail
                              = com->obuf2 + q_to_b(&tp->t_outq, com->obuf2,
                                                    sizeof com->obuf2);
                          com->obufs[1].l_next = NULL;
                          com->obufs[1].l_queued = TRUE;
                          mtx_lock_spin(&sio_lock);
                          if (com->state & CS_BUSY) {
                                  qp = com->obufq.l_next;
                                  while ((next = qp->l_next) != NULL)
                                          qp = next;
                                  qp->l_next = &com->obufs[1];
                          } else {
                                  com->obufq.l_head = com->obufs[1].l_head;
                                  com->obufq.l_tail = com->obufs[1].l_tail;
                                  com->obufq.l_next = &com->obufs[1];
                                  com->state |= CS_BUSY;
                          }
                          mtx_unlock_spin(&sio_lock);
                  }
                  tp->t_state |= TS_BUSY;
          }
          mtx_lock_spin(&sio_lock);
          if (com->state >= (CS_BUSY | CS_TTGO))
                  siointr1(com);  /* fake interrupt to start output */
          mtx_unlock_spin(&sio_lock);
          ttwwakeup(tp);
          splx(s);
  }
  
  static void
  comstop(tp, rw)
          struct tty      *tp;
          int             rw;
  {
          struct com_s    *com;
  
          com = tp->t_sc;
          if (com == NULL || com->gone)
                  return;
          mtx_lock_spin(&sio_lock);
          if (rw & FWRITE) {
                  if (com->hasfifo)
  #ifdef COM_ESP
                      /* XXX avoid h/w bug. */
                      if (!com->esp)
  #endif
                          sio_setreg(com, com_fifo,
                                     FIFO_XMT_RST | com->fifo_image);
                  com->obufs[0].l_queued = FALSE;
                  com->obufs[1].l_queued = FALSE;
                  if (com->state & CS_ODONE)
                          com_events -= LOTS_OF_EVENTS;
                  com->state &= ~(CS_ODONE | CS_BUSY);
                  com->tp->t_state &= ~TS_BUSY;
          }
          if (rw & FREAD) {
                  if (com->hasfifo)
  #ifdef COM_ESP
                      /* XXX avoid h/w bug. */
                      if (!com->esp)
  #endif
                          sio_setreg(com, com_fifo,
                                     FIFO_RCV_RST | com->fifo_image);
                  com_events -= (com->iptr - com->ibuf);
                  com->iptr = com->ibuf;
          }
          mtx_unlock_spin(&sio_lock);
          comstart(tp);
  }
  
  static int
  commodem(struct tty *tp, int sigon, int sigoff)
  {
          struct com_s    *com;
          int     bitand, bitor, msr;
  
          com = tp->t_sc;
          if (com->gone)
                  return(0);
          if (sigon != 0 || sigoff != 0) {
                  bitand = bitor = 0;
                  if (sigoff & SER_DTR)
                          bitand |= MCR_DTR;
                  if (sigoff & SER_RTS)
                          bitand |= MCR_RTS;
                  if (sigon & SER_DTR)
                          bitor |= MCR_DTR;
                  if (sigon & SER_RTS)
                          bitor |= MCR_RTS;
                  bitand = ~bitand;
                  mtx_lock_spin(&sio_lock);
                  com->mcr_image &= bitand;
                  com->mcr_image |= bitor;
                  outb(com->modem_ctl_port, com->mcr_image);
                  mtx_unlock_spin(&sio_lock);
                  return (0);
          } else {
                  bitor = 0;
                  if (com->mcr_image & MCR_DTR)
                          bitor |= SER_DTR;
                  if (com->mcr_image & MCR_RTS)
                          bitor |= SER_RTS;
                  msr = com->prev_modem_status;
                  if (msr & MSR_CTS)
                          bitor |= SER_CTS;
                  if (msr & MSR_DCD)
                          bitor |= SER_DCD;
                  if (msr & MSR_DSR)
                          bitor |= SER_DSR;
                  if (msr & MSR_DSR)
                          bitor |= SER_DSR;
                  if (msr & (MSR_RI | MSR_TERI))
                          bitor |= SER_RI;
                  return (bitor);
          }
  }
  
  static void
  siosettimeout()
  {
          struct com_s    *com;
          bool_t          someopen;
          int             unit;
  
          /*
           * Set our timeout period to 1 second if no polled devices are open.
           * Otherwise set it to max(1/200, 1/hz).
           * Enable timeouts iff some device is open.
           */
          untimeout(comwakeup, (void *)NULL, sio_timeout_handle);
          sio_timeout = hz;
          someopen = FALSE;
          for (unit = 0; unit < sio_numunits; ++unit) {
                  com = com_addr(unit);
                  if (com != NULL && com->tp != NULL
                      && com->tp->t_state & TS_ISOPEN && !com->gone) {
                          someopen = TRUE;
                          if (com->poll || com->poll_output) {
                                  sio_timeout = hz > 200 ? hz / 200 : 1;
                                  break;
                          }
                  }
          }
          if (someopen) {
                  sio_timeouts_until_log = hz / sio_timeout;
                  sio_timeout_handle = timeout(comwakeup, (void *)NULL,
                                               sio_timeout);
          } else {
                  /* Flush error messages, if any. */
                  sio_timeouts_until_log = 1;
                  comwakeup((void *)NULL);
                  untimeout(comwakeup, (void *)NULL, sio_timeout_handle);
          }
  }
  
  static void
  comwakeup(chan)
          void    *chan;
  {
          struct com_s    *com;
          int             unit;
  
          sio_timeout_handle = timeout(comwakeup, (void *)NULL, sio_timeout);
  
          /*
           * Recover from lost output interrupts.
           * Poll any lines that don't use interrupts.
           */
          for (unit = 0; unit < sio_numunits; ++unit) {
                  com = com_addr(unit);
                  if (com != NULL && !com->gone
                      && (com->state >= (CS_BUSY | CS_TTGO) || com->poll)) {
                          mtx_lock_spin(&sio_lock);
                          siointr1(com);
                          mtx_unlock_spin(&sio_lock);
                  }
          }
  
          /*
           * Check for and log errors, but not too often.
           */
          if (--sio_timeouts_until_log > 0)
                  return;
          sio_timeouts_until_log = hz / sio_timeout;
          for (unit = 0; unit < sio_numunits; ++unit) {
                  int     errnum;
  
                  com = com_addr(unit);
                  if (com == NULL)
                          continue;
                  if (com->gone)
                          continue;
                  for (errnum = 0; errnum < CE_NTYPES; ++errnum) {
                          u_int   delta;
                          u_long  total;
  
                          mtx_lock_spin(&sio_lock);
                          delta = com->delta_error_counts[errnum];
                          com->delta_error_counts[errnum] = 0;
                          mtx_unlock_spin(&sio_lock);
                          if (delta == 0)
                                  continue;
                          total = com->error_counts[errnum] += delta;
                          log(LOG_ERR, "sio%d: %u more %s%s (total %lu)\n",
                              unit, delta, error_desc[errnum],
                              delta == 1 ? "" : "s", total);
                  }
          }
  }
  
  /*
   * Following are all routines needed for SIO to act as console
   */
  struct siocnstate {
          u_char  dlbl;
          u_char  dlbh;
          u_char  ier;
          u_char  cfcr;
          u_char  mcr;
  };
  
  /*
   * This is a function in order to not replicate "ttyd%d" more
   * places than absolutely necessary.
   */
  static void
  siocnset(struct consdev *cd, int unit)
  {
  
          cd->cn_unit = unit;
          sprintf(cd->cn_name, "ttyd%d", unit);
  }
  
  static speed_t siocngetspeed(Port_t, u_long rclk);
  static void siocnclose(struct siocnstate *sp, Port_t iobase);
  static void siocnopen(struct siocnstate *sp, Port_t iobase, int speed);
  static void siocntxwait(Port_t iobase);
  
  static cn_probe_t sio_cnprobe;
  static cn_init_t sio_cninit;
  static cn_term_t sio_cnterm;
  static cn_getc_t sio_cngetc;
  static cn_putc_t sio_cnputc;
  
  CONSOLE_DRIVER(sio);
  
  static void
  siocntxwait(iobase)
          Port_t  iobase;
  {
          int     timo;
  
          /*
           * Wait for any pending transmission to finish.  Required to avoid
           * the UART lockup bug when the speed is changed, and for normal
           * transmits.
           */
          timo = 100000;
          while ((inb(iobase + com_lsr) & (LSR_TSRE | LSR_TXRDY))
                 != (LSR_TSRE | LSR_TXRDY) && --timo != 0)
                  ;
  }
  
  /*
   * Read the serial port specified and try to figure out what speed
   * it's currently running at.  We're assuming the serial port has
   * been initialized and is basicly idle.  This routine is only intended
   * to be run at system startup.
   *
   * If the value read from the serial port doesn't make sense, return 0.
   */
  
  static speed_t
  siocngetspeed(iobase, rclk)
          Port_t  iobase;
          u_long  rclk;
  {
          u_int   divisor;
          u_char  dlbh;
          u_char  dlbl;
          u_char  cfcr;
  
          cfcr = inb(iobase + com_cfcr);
          outb(iobase + com_cfcr, CFCR_DLAB | cfcr);
  
          dlbl = inb(iobase + com_dlbl);
          dlbh = inb(iobase + com_dlbh);
  
          outb(iobase + com_cfcr, cfcr);
  
          divisor = dlbh << 8 | dlbl;
  
          /* XXX there should be more sanity checking. */
          if (divisor == 0)
                  return (CONSPEED);
          return (rclk / (16UL * divisor));
  }
  
  static void
  siocnopen(sp, iobase, speed)
          struct siocnstate       *sp;
          Port_t                  iobase;
          int                     speed;
  {
          u_int   divisor;
          u_char  dlbh;
          u_char  dlbl;
  
          /*
           * Save all the device control registers except the fifo register
           * and set our default ones (cs8 -parenb speed=comdefaultrate).
           * We can't save the fifo register since it is read-only.
           */
          sp->ier = inb(iobase + com_ier);
          outb(iobase + com_ier, 0);      /* spltty() doesn't stop siointr() */
          siocntxwait(iobase);
          sp->cfcr = inb(iobase + com_cfcr);
          outb(iobase + com_cfcr, CFCR_DLAB | CFCR_8BITS);
          sp->dlbl = inb(iobase + com_dlbl);
          sp->dlbh = inb(iobase + com_dlbh);
          /*
           * Only set the divisor registers if they would change, since on
           * some 16550 incompatibles (Startech), setting them clears the
           * data input register.  This also reduces the effects of the
           * UMC8669F bug.
           */
          divisor = siodivisor(comdefaultrclk, speed);
          dlbl = divisor & 0xFF;
          if (sp->dlbl != dlbl)
                  outb(iobase + com_dlbl, dlbl);
          dlbh = divisor >> 8;
          if (sp->dlbh != dlbh)
                  outb(iobase + com_dlbh, dlbh);
          outb(iobase + com_cfcr, CFCR_8BITS);
          sp->mcr = inb(iobase + com_mcr);
          /*
           * We don't want interrupts, but must be careful not to "disable"
           * them by clearing the MCR_IENABLE bit, since that might cause
           * an interrupt by floating the IRQ line.
           */
          outb(iobase + com_mcr, (sp->mcr & MCR_IENABLE) | MCR_DTR | MCR_RTS);
  }
  
  static void
  siocnclose(sp, iobase)
          struct siocnstate       *sp;
          Port_t                  iobase;
  {
          /*
           * Restore the device control registers.
           */
          siocntxwait(iobase);
          outb(iobase + com_cfcr, CFCR_DLAB | CFCR_8BITS);
          if (sp->dlbl != inb(iobase + com_dlbl))
                  outb(iobase + com_dlbl, sp->dlbl);
          if (sp->dlbh != inb(iobase + com_dlbh))
                  outb(iobase + com_dlbh, sp->dlbh);
          outb(iobase + com_cfcr, sp->cfcr);
          /*
           * XXX damp oscillations of MCR_DTR and MCR_RTS by not restoring them.
           */
          outb(iobase + com_mcr, sp->mcr | MCR_DTR | MCR_RTS);
          outb(iobase + com_ier, sp->ier);
  }
  
  static void
  sio_cnprobe(cp)
          struct consdev  *cp;
  {
          speed_t                 boot_speed;
          u_char                  cfcr;
          u_int                   divisor;
          int                     s, unit;
          struct siocnstate       sp;
  
          /*
           * Find our first enabled console, if any.  If it is a high-level
           * console device, then initialize it and return successfully.
           * If it is a low-level console device, then initialize it and
           * return unsuccessfully.  It must be initialized in both cases
           * for early use by console drivers and debuggers.  Initializing
           * the hardware is not necessary in all cases, since the i/o
           * routines initialize it on the fly, but it is necessary if
           * input might arrive while the hardware is switched back to an
           * uninitialized state.  We can't handle multiple console devices
           * yet because our low-level routines don't take a device arg.
           * We trust the user to set the console flags properly so that we
           * don't need to probe.
           */
          cp->cn_pri = CN_DEAD;
  
          for (unit = 0; unit < 16; unit++) { /* XXX need to know how many */
                  int flags;
  
                  if (resource_disabled("sio", unit))
                          continue;
                  if (resource_int_value("sio", unit, "flags", &flags))
                          continue;
                  if (COM_CONSOLE(flags) || COM_DEBUGGER(flags)) {
                          int port;
                          Port_t iobase;
  
                          if (resource_int_value("sio", unit, "port", &port))
                                  continue;
                          iobase = port;
                          s = spltty();
                          if (boothowto & RB_SERIAL) {
                                  boot_speed =
                                      siocngetspeed(iobase, comdefaultrclk);
                                  if (boot_speed)
                                          comdefaultrate = boot_speed;
                          }
  
                          /*
                           * Initialize the divisor latch.  We can't rely on
                           * siocnopen() to do this the first time, since it 
                           * avoids writing to the latch if the latch appears
                           * to have the correct value.  Also, if we didn't
                           * just read the speed from the hardware, then we
                           * need to set the speed in hardware so that
                           * switching it later is null.
                           */
                          cfcr = inb(iobase + com_cfcr);
                          outb(iobase + com_cfcr, CFCR_DLAB | cfcr);
                          divisor = siodivisor(comdefaultrclk, comdefaultrate);
                          outb(iobase + com_dlbl, divisor & 0xff);
                          outb(iobase + com_dlbh, divisor >> 8);
                          outb(iobase + com_cfcr, cfcr);
  
                          siocnopen(&sp, iobase, comdefaultrate);
  
                          splx(s);
                          if (COM_CONSOLE(flags) && !COM_LLCONSOLE(flags)) {
                                  siocnset(cp, unit);
                                  cp->cn_pri = COM_FORCECONSOLE(flags)
                                               || boothowto & RB_SERIAL
                                               ? CN_REMOTE : CN_NORMAL;
                                  siocniobase = iobase;
                                  siocnunit = unit;
                          }
  #ifdef GDB
                          if (COM_DEBUGGER(flags))
                                  siogdbiobase = iobase;
  #endif
                  }
          }
  }
  
  static void
  sio_cninit(cp)
          struct consdev  *cp;
  {
          comconsole = cp->cn_unit;
  }
  
  static void
  sio_cnterm(cp)
          struct consdev  *cp;
  {
          comconsole = -1;
  }
  
  static int
  sio_cngetc(struct consdev *cd)
  {
          int     c;
          Port_t  iobase;
          int     s;
          struct siocnstate       sp;
          speed_t speed;
  
          if (cd != NULL && cd->cn_unit == siocnunit) {
                  iobase = siocniobase;
                  speed = comdefaultrate;
          } else {
  #ifdef GDB
                  iobase = siogdbiobase;
                  speed = gdbdefaultrate;
  #else
                  return (-1);
  #endif
          }
          s = spltty();
          siocnopen(&sp, iobase, speed);
          if (inb(iobase + com_lsr) & LSR_RXRDY)
                  c = inb(iobase + com_data);
          else
                  c = -1;
          siocnclose(&sp, iobase);
          splx(s);
          return (c);
  }
  
  static void
  sio_cnputc(struct consdev *cd, int c)
  {
          int     need_unlock;
          int     s;
          struct siocnstate       sp;
          Port_t  iobase;
          speed_t speed;
  
          if (cd != NULL && cd->cn_unit == siocnunit) {
                  iobase = siocniobase;
                  speed = comdefaultrate;
          } else {
  #ifdef GDB
                  iobase = siogdbiobase;
                  speed = gdbdefaultrate;
  #else
                  return;
  #endif
          }
          s = spltty();
          need_unlock = 0;
          if (!kdb_active && sio_inited == 2 && !mtx_owned(&sio_lock)) {
                  mtx_lock_spin(&sio_lock);
                  need_unlock = 1;
          }
          siocnopen(&sp, iobase, speed);
          siocntxwait(iobase);
          outb(iobase + com_data, c);
          siocnclose(&sp, iobase);
          if (need_unlock)
                  mtx_unlock_spin(&sio_lock);
          splx(s);
  }
  
  /*
   * Remote gdb(1) support.
   */
  
  #if defined(GDB)
  
  #include <gdb/gdb.h>
  
  static gdb_probe_f siogdbprobe;
  static gdb_init_f siogdbinit;
  static gdb_term_f siogdbterm;
  static gdb_getc_f siogdbgetc;
  static gdb_putc_f siogdbputc;
  
  GDB_DBGPORT(sio, siogdbprobe, siogdbinit, siogdbterm, siogdbgetc, siogdbputc);
  
  static int
  siogdbprobe(void)
  {
          return ((siogdbiobase != 0) ? 0 : -1);
  }
  
  static void
  siogdbinit(void)
  {
  }
  
  static void
  siogdbterm(void)
  {
  }
  
  static void
  siogdbputc(int c)
  {
          sio_cnputc(NULL, c);
  }
  
  static int
  siogdbgetc(void)
  {
          return (sio_cngetc(NULL));
  }
  
  #endif

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