1README on the ADC/Touchscreen Controller 2======================================== 3 4The LH79524 and LH7A404 include a built-in Analog to Digital 5controller (ADC) that is used to process input from a touchscreen. 6The driver only implements a four-wire touch panel protocol. 7 8The touchscreen driver is maintenance free except for the pen-down or 9touch threshold. Some resistive displays and board combinations may 10require tuning of this threshold. The driver exposes some of its 11internal state in the sys filesystem. If the kernel is configured 12with it, CONFIG_SYSFS, and sysfs is mounted at /sys, there will be a 13directory 14 15 /sys/devices/platform/adc-lh7.0 16 17containing these files. 18 19 -r--r--r-- 1 root root 4096 Jan 1 00:00 samples 20 -rw-r--r-- 1 root root 4096 Jan 1 00:00 threshold 21 -r--r--r-- 1 root root 4096 Jan 1 00:00 threshold_range 22 23The threshold is the current touch threshold. It defaults to 750 on 24most targets. 25 26 # cat threshold 27 750 28 29The threshold_range contains the range of valid values for the 30threshold. Values outside of this range will be silently ignored. 31 32 # cat threshold_range 33 0 1023 34 35To change the threshold, write a value to the threshold file. 36 37 # echo 500 > threshold 38 # cat threshold 39 500 40 41The samples file contains the most recently sampled values from the 42ADC. There are 12. Below are typical of the last sampled values when 43the pen has been released. The first two and last two samples are for 44detecting whether or not the pen is down. The third through sixth are 45X coordinate samples. The seventh through tenth are Y coordinate 46samples. 47 48 # cat samples 49 1023 1023 0 0 0 0 530 529 530 529 1023 1023 50 51To determine a reasonable threshold, press on the touch panel with an 52appropriate stylus and read the values from samples. 53 54 # cat samples 55 1023 676 92 103 101 102 855 919 922 922 1023 679 56 57The first and eleventh samples are discarded. Thus, the important 58values are the second and twelfth which are used to determine if the 59pen is down. When both are below the threshold, the driver registers 60that the pen is down. When either is above the threshold, it 61registers then pen is up. 62