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[linux-2.6.git] / Documentation / arm / Sharp-LH / ADC-LH7-Touchscreen

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+README on the ADC/Touchscreen Controller
+========================================
+
+The LH79524 and LH7A404 include a built-in Analog to Digital
+controller (ADC) that is used to process input from a touchscreen.
+The driver only implements a four-wire touch panel protocol.
+
+The touchscreen driver is maintenance free except for the pen-down or
+touch threshold.  Some resistive displays and board combinations may
+require tuning of this threshold.  The driver exposes some of it's
+internal state in the sys filesystem.  If the kernel is configured
+with it, CONFIG_SYSFS, and sysfs is mounted at /sys, there will be a
+directory
+
+  /sys/devices/platform/adc-lh7.0
+
+containing these files.
+
+  -r--r--r--    1 root     root         4096 Jan  1 00:00 samples
+  -rw-r--r--    1 root     root         4096 Jan  1 00:00 threshold
+  -r--r--r--    1 root     root         4096 Jan  1 00:00 threshold_range
+
+The threshold is the current touch threshold.  It defaults to 750 on
+most targets.
+
+  # cat threshold
+ 750
+
+The threshold_range contains the range of valid values for the
+threshold.  Values outside of this range will be silently ignored.
+
+  # cat threshold_range
+  0 1023
+
+To change the threshold, write a value to the threshold file.
+
+  # echo 500 > threshold
+  # cat threshold
+  500
+
+The samples file contains the most recently sampled values from the
+ADC.  There are 12.  Below are typical of the last sampled values when
+the pen has been released.  The first two and last two samples are for
+detecting whether or not the pen is down.  The third through sixth are
+X coordinate samples.  The seventh through tenth are Y coordinate
+samples.
+
+  # cat samples
+  1023 1023 0 0 0 0 530 529 530 529 1023 1023
+
+To determine a reasonable threshold, press on the touch panel with an
+appropriate stylus and read the values from samples.
+
+  # cat samples
+  1023 676 92 103 101 102 855 919 922 922 1023 679
+
+The first and eleventh samples are discarded.  Thus, the important
+values are the second and twelfth which are used to determine if the
+pen is down.  When both are below the threshold, the driver registers
+that the pen is down.  When either is above the threshold, it
+registers then pen is up.