diff options
Diffstat (limited to 'Documentation/arm')
| -rw-r--r-- | Documentation/arm/Sharp-LH/ADC-LH7-Touchscreen | 61 | ||||
| -rw-r--r-- | Documentation/arm/Sharp-LH/LCDPanels | 59 |
2 files changed, 120 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 00000000000..1e6a23fdf2f --- /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. diff --git a/Documentation/arm/Sharp-LH/LCDPanels b/Documentation/arm/Sharp-LH/LCDPanels new file mode 100644 index 00000000000..fb1b21c2f2f --- /dev/null +++ b/Documentation/arm/Sharp-LH/LCDPanels @@ -0,0 +1,59 @@ +README on the LCD Panels +======================== + +Configuration options for several LCD panels, available from Logic PD, +are included in the kernel source. This README will help you +understand the configuration data and give you some guidance for +adding support for other panels if you wish. + + +lcd-panels.h +------------ + +There is no way, at present, to detect which panel is attached to the +system at runtime. Thus the kernel configuration is static. The file +arch/arm/mach-ld7a40x/lcd-panels.h (or similar) defines all of the +panel specific parameters. + +It should be possible for this data to be shared among several device +families. The current layout may be insufficiently general, but it is +amenable to improvement. + + +PIXEL_CLOCK +----------- + +The panel data sheets will give a range of acceptable pixel clocks. +The fundamental LCDCLK input frequency is divided down by a PCD +constant in field '.tim2'. It may happen that it is impossible to set +the pixel clock within this range. A clock which is too slow will +tend to flicker. For the highest quality image, set the clock as high +as possible. + + +MARGINS +------- + +These values may be difficult to glean from the panel data sheet. In +the case of the Sharp panels, the upper margin is explicitly called +out as a specific number of lines from the top of the frame. The +other values may not matter as much as the panels tend to +automatically center the image. + + +Sync Sense +---------- + +The sense of the hsync and vsync pulses may be called out in the data +sheet. On one panel, the sense of these pulses determine the height +of the visible region on the panel. Most of the Sharp panels use +negative sense sync pulses set by the TIM2_IHS and TIM2_IVS bits in +'.tim2'. + + +Pel Layout +---------- + +The Sharp color TFT panels are all configured for 16 bit direct color +modes. The amba-lcd driver sets the pel mode to 565 for 5 bits of +each red and blue and 6 bits of green. |