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Diffstat (limited to 'Documentation/arm/Sharp-LH/ADC-LH7-Touchscreen')
| -rw-r--r-- | Documentation/arm/Sharp-LH/ADC-LH7-Touchscreen | 61 |
1 files changed, 61 insertions, 0 deletions
diff --git a/Documentation/arm/Sharp-LH/ADC-LH7-Touchscreen b/Documentation/arm/Sharp-LH/ADC-LH7-Touchscreen new file mode 100644 index 000000000000..1e6a23fdf2fc --- /dev/null +++ b/Documentation/arm/Sharp-LH/ADC-LH7-Touchscreen @@ -0,0 +1,61 @@ +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. |