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ADC-LH7-Touchscreen

ADC-LH7-Touchscreen 2.1 KB
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  1. README on the ADC/Touchscreen Controller
    2. 

  2. ========================================
    3. 

  3. 

  4. The LH79524 and LH7A404 include a built-in Analog to Digital
    5. 

  5. controller (ADC) that is used to process input from a touchscreen.
    6. 

  6. The driver only implements a four-wire touch panel protocol.
    7. 

  7. 

  8. The touchscreen driver is maintenance free except for the pen-down or
    9. 

  9. touch threshold.  Some resistive displays and board combinations may
    10. 

  10. require tuning of this threshold.  The driver exposes some of it's
    11. 

  11. internal state in the sys filesystem.  If the kernel is configured
    12. 

  12. with it, CONFIG_SYSFS, and sysfs is mounted at /sys, there will be a
    13. 

  13. directory
    14. 

  14. 

  15.   /sys/devices/platform/adc-lh7.0
    16. 

  16. 

  17. containing these files.
    18. 

  18. 

  19.   -r--r--r--    1 root     root         4096 Jan  1 00:00 samples
    20. 

  20.   -rw-r--r--    1 root     root         4096 Jan  1 00:00 threshold
    21. 

  21.   -r--r--r--    1 root     root         4096 Jan  1 00:00 threshold_range
    22. 

  22. 

  23. The threshold is the current touch threshold.  It defaults to 750 on
    24. 

  24. most targets.
    25. 

  25. 

  26.   # cat threshold
    27. 

  27.  750
    28. 

  28. 

  29. The threshold_range contains the range of valid values for the
    30. 

  30. threshold.  Values outside of this range will be silently ignored.
    31. 

  31. 

  32.   # cat threshold_range
    33. 

  33.   0 1023
    34. 

  34. 

  35. To change the threshold, write a value to the threshold file.
    36. 

  36. 

  37.   # echo 500 > threshold
    38. 

  38.   # cat threshold
    39. 

  39.   500
    40. 

  40. 

  41. The samples file contains the most recently sampled values from the
    42. 

  42. ADC.  There are 12.  Below are typical of the last sampled values when
    43. 

  43. the pen has been released.  The first two and last two samples are for
    44. 

  44. detecting whether or not the pen is down.  The third through sixth are
    45. 

  45. X coordinate samples.  The seventh through tenth are Y coordinate
    46. 

  46. samples.
    47. 

  47. 

  48.   # cat samples
    49. 

  49.   1023 1023 0 0 0 0 530 529 530 529 1023 1023
    50. 

  50. 

  51. To determine a reasonable threshold, press on the touch panel with an
    52. 

  52. appropriate stylus and read the values from samples.
    53. 

  53. 

  54.   # cat samples
    55. 

  55.   1023 676 92 103 101 102 855 919 922 922 1023 679
    56. 

  56. 

  57. The first and eleventh samples are discarded.  Thus, the important
    58. 

  58. values are the second and twelfth which are used to determine if the
    59. 

  59. pen is down.  When both are below the threshold, the driver registers
    60. 

  60. that the pen is down.  When either is above the threshold, it
    61. 

  61. registers then pen is up.
    62.