The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/Documentation/input/alps.txt

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    1 ALPS Touchpad Protocol
    2 ----------------------
    3 
    4 Introduction
    5 ------------
    6 
    7 Currently the ALPS touchpad driver supports four protocol versions in use by
    8 ALPS touchpads, called versions 1, 2, 3, and 4. Information about the various
    9 protocol versions is contained in the following sections.
   10 
   11 Detection
   12 ---------
   13 
   14 All ALPS touchpads should respond to the "E6 report" command sequence:
   15 E8-E6-E6-E6-E9. An ALPS touchpad should respond with either 00-00-0A or
   16 00-00-64 if no buttons are pressed. The bits 0-2 of the first byte will be 1s
   17 if some buttons are pressed.
   18 
   19 If the E6 report is successful, the touchpad model is identified using the "E7
   20 report" sequence: E8-E7-E7-E7-E9. The response is the model signature and is
   21 matched against known models in the alps_model_data_array.
   22 
   23 With protocol versions 3 and 4, the E7 report model signature is always
   24 73-02-64. To differentiate between these versions, the response from the
   25 "Enter Command Mode" sequence must be inspected as described below.
   26 
   27 Command Mode
   28 ------------
   29 
   30 Protocol versions 3 and 4 have a command mode that is used to read and write
   31 one-byte device registers in a 16-bit address space. The command sequence
   32 EC-EC-EC-E9 places the device in command mode, and the device will respond
   33 with 88-07 followed by a third byte. This third byte can be used to determine
   34 whether the devices uses the version 3 or 4 protocol.
   35 
   36 To exit command mode, PSMOUSE_CMD_SETSTREAM (EA) is sent to the touchpad.
   37 
   38 While in command mode, register addresses can be set by first sending a
   39 specific command, either EC for v3 devices or F5 for v4 devices. Then the
   40 address is sent one nibble at a time, where each nibble is encoded as a
   41 command with optional data. This enoding differs slightly between the v3 and
   42 v4 protocols.
   43 
   44 Once an address has been set, the addressed register can be read by sending
   45 PSMOUSE_CMD_GETINFO (E9). The first two bytes of the response contains the
   46 address of the register being read, and the third contains the value of the
   47 register. Registers are written by writing the value one nibble at a time
   48 using the same encoding used for addresses.
   49 
   50 Packet Format
   51 -------------
   52 
   53 In the following tables, the following notation is used.
   54 
   55  CAPITALS = stick, miniscules = touchpad
   56 
   57 ?'s can have different meanings on different models, such as wheel rotation,
   58 extra buttons, stick buttons on a dualpoint, etc.
   59 
   60 PS/2 packet format
   61 ------------------
   62 
   63  byte 0:  0    0 YSGN XSGN    1    M    R    L
   64  byte 1: X7   X6   X5   X4   X3   X2   X1   X0
   65  byte 2: Y7   Y6   Y5   Y4   Y3   Y2   Y1   Y0
   66 
   67 Note that the device never signals overflow condition.
   68 
   69 ALPS Absolute Mode - Protocol Verion 1
   70 --------------------------------------
   71 
   72  byte 0:  1    0    0    0    1   x9   x8   x7
   73  byte 1:  0   x6   x5   x4   x3   x2   x1   x0
   74  byte 2:  0    ?    ?    l    r    ?  fin  ges
   75  byte 3:  0    ?    ?    ?    ?   y9   y8   y7
   76  byte 4:  0   y6   y5   y4   y3   y2   y1   y0
   77  byte 5:  0   z6   z5   z4   z3   z2   z1   z0
   78 
   79 ALPS Absolute Mode - Protocol Version 2
   80 ---------------------------------------
   81 
   82  byte 0:  1    ?    ?    ?    1    ?    ?    ?
   83  byte 1:  0   x6   x5   x4   x3   x2   x1   x0
   84  byte 2:  0  x10   x9   x8   x7    ?  fin  ges
   85  byte 3:  0   y9   y8   y7    1    M    R    L
   86  byte 4:  0   y6   y5   y4   y3   y2   y1   y0
   87  byte 5:  0   z6   z5   z4   z3   z2   z1   z0
   88 
   89 Dualpoint device -- interleaved packet format
   90 ---------------------------------------------
   91 
   92  byte 0:    1    1    0    0    1    1    1    1
   93  byte 1:    0   x6   x5   x4   x3   x2   x1   x0
   94  byte 2:    0  x10   x9   x8   x7    0  fin  ges
   95  byte 3:    0    0 YSGN XSGN    1    1    1    1
   96  byte 4:   X7   X6   X5   X4   X3   X2   X1   X0
   97  byte 5:   Y7   Y6   Y5   Y4   Y3   Y2   Y1   Y0
   98  byte 6:    0   y9   y8   y7    1    m    r    l
   99  byte 7:    0   y6   y5   y4   y3   y2   y1   y0
  100  byte 8:    0   z6   z5   z4   z3   z2   z1   z0
  101 
  102 ALPS Absolute Mode - Protocol Version 3
  103 ---------------------------------------
  104 
  105 ALPS protocol version 3 has three different packet formats. The first two are
  106 associated with touchpad events, and the third is associatd with trackstick
  107 events.
  108 
  109 The first type is the touchpad position packet.
  110 
  111  byte 0:    1    ?   x1   x0    1    1    1    1
  112  byte 1:    0  x10   x9   x8   x7   x6   x5   x4
  113  byte 2:    0  y10   y9   y8   y7   y6   y5   y4
  114  byte 3:    0    M    R    L    1    m    r    l
  115  byte 4:    0   mt   x3   x2   y3   y2   y1   y0
  116  byte 5:    0   z6   z5   z4   z3   z2   z1   z0
  117 
  118 Note that for some devices the trackstick buttons are reported in this packet,
  119 and on others it is reported in the trackstick packets.
  120 
  121 The second packet type contains bitmaps representing the x and y axes. In the
  122 bitmaps a given bit is set if there is a finger covering that position on the
  123 given axis. Thus the bitmap packet can be used for low-resolution multi-touch
  124 data, although finger tracking is not possible.  This packet also encodes the
  125 number of contacts (f1 and f0 in the table below).
  126 
  127  byte 0:    1    1   x1   x0    1    1    1    1
  128  byte 1:    0   x8   x7   x6   x5   x4   x3   x2
  129  byte 2:    0   y7   y6   y5   y4   y3   y2   y1
  130  byte 3:    0  y10   y9   y8    1    1    1    1
  131  byte 4:    0  x14  x13  x12  x11  x10   x9   y0
  132  byte 5:    0    1    ?    ?    ?    ?   f1   f0
  133 
  134 This packet only appears after a position packet with the mt bit set, and
  135 usually only appears when there are two or more contacts (although
  136 occasionally it's seen with only a single contact).
  137 
  138 The final v3 packet type is the trackstick packet.
  139 
  140  byte 0:    1    1   x7   y7    1    1    1    1
  141  byte 1:    0   x6   x5   x4   x3   x2   x1   x0
  142  byte 2:    0   y6   y5   y4   y3   y2   y1   y0
  143  byte 3:    0    1    0    0    1    0    0    0
  144  byte 4:    0   z4   z3   z2   z1   z0    ?    ?
  145  byte 5:    0    0    1    1    1    1    1    1
  146 
  147 ALPS Absolute Mode - Protocol Version 4
  148 ---------------------------------------
  149 
  150 Protocol version 4 has an 8-byte packet format.
  151 
  152  byte 0:    1    ?   x1   x0    1    1    1    1
  153  byte 1:    0  x10   x9   x8   x7   x6   x5   x4
  154  byte 2:    0  y10   y9   y8   y7   y6   y5   y4
  155  byte 3:    0    1   x3   x2   y3   y2   y1   y0
  156  byte 4:    0    ?    ?    ?    1    ?    r    l
  157  byte 5:    0   z6   z5   z4   z3   z2   z1   z0
  158  byte 6:    bitmap data (described below)
  159  byte 7:    bitmap data (described below)
  160 
  161 The last two bytes represent a partial bitmap packet, with 3 full packets
  162 required to construct a complete bitmap packet.  Once assembled, the 6-byte
  163 bitmap packet has the following format:
  164 
  165  byte 0:    0    1   x7   x6   x5   x4   x3   x2
  166  byte 1:    0   x1   x0   y4   y3   y2   y1   y0
  167  byte 2:    0    0    ?  x14  x13  x12  x11  x10
  168  byte 3:    0   x9   x8   y9   y8   y7   y6   y5
  169  byte 4:    0    0    0    0    0    0    0    0
  170  byte 5:    0    0    0    0    0    0    0  y10
  171 
  172 There are several things worth noting here.
  173 
  174  1) In the bitmap data, bit 6 of byte 0 serves as a sync byte to
  175     identify the first fragment of a bitmap packet.
  176 
  177  2) The bitmaps represent the same data as in the v3 bitmap packets, although
  178     the packet layout is different.
  179 
  180  3) There doesn't seem to be a count of the contact points anywhere in the v4
  181     protocol packets. Deriving a count of contact points must be done by
  182     analyzing the bitmaps.
  183 
  184  4) There is a 3 to 1 ratio of position packets to bitmap packets. Therefore
  185     MT position can only be updated for every third ST position update, and
  186     the count of contact points can only be updated every third packet as
  187     well.
  188 
  189 So far no v4 devices with tracksticks have been encountered.

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