ti-tsc-adc.txt

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    1 * TI - TSC ADC (Touschscreen and analog digital converter)
    2 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    3 
    4 Required properties:
    5 - mfd
    6         compatible: Should be
    7                 "ti,am3359-tscadc" for AM335x/AM437x SoCs
    8                 "ti,am654-tscadc", "ti,am3359-tscadc" for AM654 SoCs
    9 - child "tsc"
   10         compatible: Should be "ti,am3359-tsc".
   11         ti,wires: Wires refer to application modes i.e. 4/5/8 wire touchscreen
   12                   support on the platform.
   13         ti,x-plate-resistance: X plate resistance
   14         ti,coordinate-readouts: The sequencer supports a total of 16
   15                                 programmable steps each step is used to
   16                                 read a single coordinate. A single
   17                                 readout is enough but multiple reads can
   18                                 increase the quality.
   19                                 A value of 5 means, 5 reads for X, 5 for
   20                                 Y and 2 for Z (always). This utilises 12
   21                                 of the 16 software steps available. The
   22                                 remaining 4 can be used by the ADC.
   23         ti,wire-config: Different boards could have a different order for
   24                         connecting wires on touchscreen. We need to provide an
   25                         8 bit number where in the 1st four bits represent the
   26                         analog lines and the next 4 bits represent positive/
   27                         negative terminal on that input line. Notations to
   28                         represent the input lines and terminals resoectively
   29                         is as follows:
   30                         AIN0 = 0, AIN1 = 1 and so on till AIN7 = 7.
   31                         XP  = 0, XN = 1, YP = 2, YN = 3.
   32 - child "adc"
   33         compatible: Should be
   34                     "ti,am3359-adc" for AM335x/AM437x SoCs
   35                     "ti,am654-adc", "ti,am3359-adc" for AM654 SoCs
   36         ti,adc-channels: List of analog inputs available for ADC.
   37                          AIN0 = 0, AIN1 = 1 and so on till AIN7 = 7.
   38 
   39 Optional properties:
   40 - child "tsc"
   41         ti,charge-delay: Length of touch screen charge delay step in terms of
   42                          ADC clock cycles. Charge delay value should be large
   43                          in order to avoid false pen-up events. This value
   44                          effects the overall sampling speed, hence need to be
   45                          kept as low as possible, while avoiding false pen-up
   46                          event. Start from a lower value, say 0x400, and
   47                          increase value until false pen-up events are avoided.
   48                          The pen-up detection happens immediately after the
   49                          charge step, so this does in fact function as a
   50                          hardware knob for adjusting the amount of "settling
   51                          time".
   52 
   53 - child "adc"
   54         ti,chan-step-opendelay: List of open delays for each channel of
   55                                 ADC in the order of ti,adc-channels. The
   56                                 value corresponds to the number of ADC
   57                                 clock cycles to wait after applying the
   58                                 step configuration registers and before
   59                                 sending the start of ADC conversion.
   60                                 Maximum value is 0x3FFFF.
   61        ti,chan-step-sampledelay: List of sample delays for each channel
   62                                   of ADC in the order of ti,adc-channels.
   63                                   The value corresponds to the number of
   64                                   ADC clock cycles to sample (to hold
   65                                   start of conversion high).
   66                                   Maximum value is 0xFF.
   67        ti,chan-step-avg: Number of averages to be performed for each
   68                           channel of ADC. If average is 16 then input
   69                           is sampled 16 times and averaged to get more
   70                           accurate value. This increases the time taken
   71                           by ADC to generate a sample. Valid range is 0
   72                           average to 16 averages. Maximum value is 16.
   73 
   74 Example:
   75         tscadc: tscadc@44e0d000 {
   76                 compatible = "ti,am3359-tscadc";
   77                 tsc {
   78                         ti,wires = <4>;
   79                         ti,x-plate-resistance = <200>;
   80                         ti,coordiante-readouts = <5>;
   81                         ti,wire-config = <0x00 0x11 0x22 0x33>;
   82                         ti,charge-delay = <0x400>;
   83                 };
   84 
   85                 adc {
   86                         ti,adc-channels = <4 5 6 7>;
   87                         ti,chan-step-opendelay = <0x098 0x3ffff 0x098 0x0>;
   88                         ti,chan-step-sampledelay = <0xff 0x0 0xf 0x0>;
   89                         ti,chan-step-avg = <16 2 4 8>;
   90                 };
   91         }

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sys/contrib/device-tree/Bindings/input/touchscreen/ti-tsc-adc.txt