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authorRussell King <rmk+kernel@arm.linux.org.uk>2011-01-21 06:04:45 -0500
committerRussell King <rmk+kernel@arm.linux.org.uk>2011-01-24 14:05:19 -0500
commit82e6923e1862428b755ec306b3dbccf926849314 (patch)
treee0be095c30c7cbfeff2a2096cf53e9c2f92fed13 /Documentation/arm/Sharp-LH/ADC-LH7-Touchscreen
parent1bae4ce27c9c90344f23c65ea6966c50ffeae2f5 (diff)
ARM: lh7a40x: remove unmaintained platform support
lh7a40x has only been receiving updates for updates to generic code. The last involvement from the maintainer according to the git logs was in 2006. As such, it is a maintainence burden with no benefit. This gets rid of two defconfigs. Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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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.