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This version (11 Feb 2016 21:12) was approved by Lars-Peter Clausen.The Previously approved version (05 Sep 2012 14:12) is available.
Table of Contents
AD7879 Input Touch Screen Digitizer Linux Driver
Supported Devices
Evaluation Boards
Description
The AD7879/AD7889 is a 12-bit successive approximation ADC with a synchronous serial interface and low on-resistance switches for driving 4-wire resistive touch screens. The AD7879 works with a very low power supply, a single 1.6 V to 3.6V, and features throughput rates of 105 kSPS.
The device includes a shutdown mode, which reduces its current consumption to less than 5 uA.
To reduce the effects of noise from LCDs and other sources, the AD7879 contains a preprocessing block. The preprocessing function consists of a median and an averaging filter. The combination of these two techniques provides a more robust solution, discarding the spurious noise in the signal and keeping only the data of interest. The size of both filters is programmable. Other user-programmable conversion controls include variable acquisition time, and first conversion delay. Up to 16 averages can be taken per conversion. The AD7879 can run in either slave or stand-alone mode, using an automatic conversion sequencer and timer.
The AD7879 has a programmable pin that can operate as either an auxiliary input to the ADC, as a battery monitor, or as a GPIO. There is a programmable interrupt output which can operate in three modes, as a general purpose interrupt to signal when new data is available INT, as an interrupt to indicate when limits are exceeded, or as a pen down interrupt when the screen is touched, PENIRQ. The AD7879 offers temperature and touch-pressure measurement.
It is available in various packages. It has either an SPI (AD7879)(AD7889) or I2C (AD7879-1)(AD7889-1) interface.
See also: uclinux-dist:tslib
See also: AD7877 Touchscreen Device Driver
Configuration
AD7879-1/AD7889-1 I2C Device Address options:
| ADD1 | ADD0 | I2C Address |
|---|---|---|
| 0 | 0 | 0x2C |
| 0 | 1 | 0x2D |
| 1 | 0 | 0x2E |
| 1 | 1 | 0x2F |
Software configurable features
Software configurable:
- First Conversion Delay (128us..4.096ms in steps up 128us)
- Acquisition Time (2us, 4us, 8us, 16us)
- Average Filter (2,4,8,16)
- Median Filter (0,4,8,16)
- Pen Down Acquisition Interval Timer (550us..9.44ms in steps of 35us)
- Auxiliary GPIO can be exported to GPIOLIB, and therefore used system-wide
Source Code
Status
Files
| Function | File |
|---|---|
| driver | drivers/input/touchscreen/ad7879.c |
| i2c bus support | drivers/input/touchscreen/ad7879-i2c.c |
| spi bus support | drivers/input/touchscreen/ad7879-spi.c |
| include | include/linux/spi/ad7879.h |
Example platform device initialization
For compile time configuration, it’s common Linux practice to keep board- and application-specific configuration out of the main driver file, instead putting it into the board support file.
For devices on custom boards, as typical of embedded and SoC-(system-on-chip) based hardware, Linux uses platform_data to point to board-specific structures describing devices and how they are connected to the SoC. This can include available ports, chip variants, preferred modes, default initialization, additional pin roles, and so on. This shrinks the board-support packages (BSPs) and minimizes board and application specific #ifdefs in drivers.
Touchscreen characteristics vary between boards and models. The platform_data for the device's “struct device” holds this information.
<source trunk/include/linux/spi/ad7879.h c linux-kernel>
Example Platform / Board file (SPI Interface Version)
Declaring SPI slave devices
Unlike PCI or USB devices, SPI devices are not enumerated at the hardware level. Instead, the software must know which devices are connected on each SPI bus segment, and what slave selects these devices are using. For this reason, the kernel code must instantiate SPI devices explicitly. The most common method is to declare the SPI devices by bus number.
This method is appropriate when the SPI bus is a system bus, as in many embedded systems, wherein each SPI bus has a number which is known in advance. It is thus possible to pre-declare the SPI devices that inhabit this bus. This is done with an array of struct spi_board_info, which is registered by calling spi_register_board_info().
For more information see: Documentation/spi/spi-summary.rst
These snippets are all from the same file. arch/blackfin/mach-bf537/boards/stamp.c:
#include <linux/spi/ad7879.h> static const struct ad7879_platform_data bfin_ad7879_ts_info = { .model = 7879, /* Model = AD7879 */ .x_plate_ohms = 620, /* 620 Ohm from the touch datasheet */ .pressure_max = 10000, .pressure_min = 0, .first_conversion_delay = 3, /* wait 512us before do a first conversion */ .acquisition_time = 1, /* 4us acquisition time per sample */ .median = 2, /* do 8 measurements */ .averaging = 1, /* take the average of 4 middle samples */ .pen_down_acc_interval = 255, /* 9.4 ms */ .gpio_export = 1, /* Export GPIO to gpiolib */ .gpio_base = -1, /* Dynamic allocation */ };
static struct spi_board_info bfin_spi_board_info[] __initdata = { #if defined(CONFIG_TOUCHSCREEN_AD7879_SPI) || defined(CONFIG_TOUCHSCREEN_AD7879_SPI_MODULE) { .modalias = "ad7879", .platform_data = &bfin_ad7879_ts_info, .irq = IRQ_PF7, .max_speed_hz = 5000000, /* max spi clock (SCK) speed in HZ */ .bus_num = 0, .chip_select = 1, .controller_data = &spi_ad7879_chip_info, /* only needed on Blackfin */ .mode = SPI_CPHA | SPI_CPOL, }, #endif };
Example Platform / Board file (I2C Interface Version)
Declaring I2C devices
Unlike PCI or USB devices, I2C devices are not enumerated at the hardware level. Instead, the software must know which devices are connected on each I2C bus segment, and what address these devices are using. For this reason, the kernel code must instantiate I2C devices explicitly. There are different ways to achieve this, depending on the context and requirements. However the most common method is to declare the I2C devices by bus number.
This method is appropriate when the I2C bus is a system bus, as in many embedded systems, wherein each I2C bus has a number which is known in advance. It is thus possible to pre-declare the I2C devices that inhabit this bus. This is done with an array of struct i2c_board_info, which is registered by calling i2c_register_board_info().
So, to enable such a driver one need only edit the board support file by adding an appropriate entry to i2c_board_info.
For more information see: Documentation/i2c/instantiating-devices.rst
#include <linux/spi/ad7879.h> static const struct ad7879_platform_data bfin_ad7879_ts_info = { .model = 7879, /* Model = AD7879 */ .x_plate_ohms = 620, /* 620 Ohm from the touch datasheet */ .pressure_max = 10000, .pressure_min = 0, .first_conversion_delay = 3, /* wait 512us before do a first conversion */ .acquisition_time = 1, /* 4us acquisition time per sample */ .median = 2, /* do 8 measurements */ .averaging = 1, /* take the average of 4 middle samples */ .pen_down_acc_interval = 255, /* 9.4 ms */ .gpio_export = 1, /* Export GPIO to gpiolib */ .gpio_base = -1, /* Dynamic allocation */ };
static struct i2c_board_info __initdata bfin_i2c_board_info[] = { #if defined(CONFIG_TOUCHSCREEN_AD7879_I2C) || defined(CONFIG_TOUCHSCREEN_AD7879_I2C_MODULE) { I2C_BOARD_INFO("ad7879", 0x2F), .irq = IRQ_PG5, .platform_data = (void *)&bfin_ad7879_ts_info, }, #endif }
Adding Linux driver support
Configure kernel with “make menuconfig” (alternatively use “make xconfig” or “make qconfig”)
The AD7879 Driver depends on CONFIG_SPI or CONFIG_I2C
Input device support
-*- Generic input layer (needed for keyboard, mouse, ...)
< > Support for memoryless force-feedback devices
< > Polled input device skeleton
< > Sparse keymap support library
*** Userland interfaces ***
< > Mouse interface
< > Joystick interface
<*> Event interface
< > Event debugging
*** Input Device Drivers ***
[ ] Keyboards --->
[ ] Mice --->
[ ] Joysticks/Gamepads --->
[ ] Tablets --->
[*] Touchscreens --->
--- Touchscreens
< > ADS7846/TSC2046/AD7873 and AD(S)7843 based touchscreens (NEW)
< > AD7877 based touchscreens
<*> Analog Devices AD7879-1/AD7889-1 touchscreen interface (NEW)
<*> support I2C bus connection
< > support SPI bus connection (NEW)
[ ] Miscellaneous devices --->
Hardware I/O ports --->
Hardware configuration
Driver testing
Driver compiled as a module
root:~> modprobe evdev root:~> modprobe ad7879 input: AD7879 Touchscreen as /class/input/input0 ad7879 spi0.1: touchscreen, irq 57
Driver compiled into the kernel
Your kernel startup messages should include something like this
input: AD7879 Touchscreen as /class/input/input0 ad7879 spi0.1: touchscreen, irq 57
Common Problems
In case you see a message like this
spi0.1: Failed to probe AD7879 Touchscreen
This means that the SPI communication and initialization with the AD7879 touchscreen controller/digitizer failed. check bus_num and chip_select in your platform device file
Checking for proper installation
After the kernel boot your device folder should include at least one device node for the touchscreen
root:/> ls -al /dev/input/ drw-r--r-- 2 root root 0 Jan 1 00:03 . drwxr-xr-x 5 root root 0 Jan 1 00:03 .. crw-rw-r-- 1 root root 13, 64 Jan 1 00:03 event0 crw-rw-r-- 1 root root 13, 65 Jan 1 00:03 event1 crw-rw-r-- 1 root root 13, 66 Jan 1 00:03 event2 root:/>
Check that the interrupt is registered.
root:~> cat /proc/interrupts | grep ad7879 57: 0 ad7879
root:~> cat /sys/class/input/input0/name AD7879 Touchscreen
Use the event_test utility to test proper function
root:/> event_test /dev/input/event0
Input driver version is 1.0.0
Input device ID: bus 0x0 vendor 0x0 product 0x0 version 0x0
Input device name: "AD7879 Touchscreen"
Supported events:
Event type 0 (Sync)
Event type 1 (Key)
Event code 330 (Touch)
Event type 3 (Absolute)
Event code 0 (X)
Value 1268
Min 0
Max 4095
Event code 1 (Y)
Value 1250
Min 0
Max 4095
Event code 24 (Pressure)
Value 0
Min 0
Max 10000
Testing ... (interrupt to exit)
Event: time 67435.364000, type 1 (Key), code 330 (Touch), value 1
Event: time 67435.364000, type 3 (Absolute), code 0 (X), value 1624
Event: time 67435.364000, type 3 (Absolute), code 1 (Y), value 1514
Event: time 67435.364000, type 3 (Absolute), code 24 (Pressure), value 349
Event: time 67435.364000, -------------- Report Sync ------------
Event: time 67435.408000, type 3 (Absolute), code 0 (X), value 1626
Event: time 67435.408000, type 3 (Absolute), code 1 (Y), value 1516
Event: time 67435.408000, type 3 (Absolute), code 24 (Pressure), value 342
Event: time 67435.408000, -------------- Report Sync ------------
Event: time 67435.452000, type 3 (Absolute), code 1 (Y), value 1514
Event: time 67435.452000, type 3 (Absolute), code 24 (Pressure), value 339
Event: time 67435.452000, -------------- Report Sync ------------
Event: time 67435.496000, type 3 (Absolute), code 0 (X), value 1625
Event: time 67435.496000, type 3 (Absolute), code 24 (Pressure), value 343
Event: time 67435.496000, -------------- Report Sync ------------
Event: time 67435.596000, type 3 (Absolute), code 24 (Pressure), value 0
Event: time 67435.596000, type 1 (Key), code 330 (Touch), value 0
Event: time 67435.596000, -------------- Report Sync ------------
In case you touch the surface and don't receive events, it's likely that something with your /DAV Interrupt is wrong.
check irq number in your platform device file
In case you get a message like: evtest: No such device, it's likely that you have not install the necessary modules
root:/> cat /proc/interrupts 6: 7898 Blackfin Core Timer 10: 1 rtc-bfin 18: 0 BFIN_UART_RX 19: 105 BFIN_UART_TX 24: 77 EMAC_RX 42: 0 PPI ERROR 57: 168 ad7879 Err: 0 root:/>
Find Input by name
In case you like to find out which input/event interface is connected to your touchscreen, use the sysfs entries
root:/sys/class/input> for i in `find /sys/class/input/ -name name` ; do echo -n "$i : "; cat $i; done ./input2/name : Logitech USB Receive ./input1/name : Logitech USB Receiver ./input0/name : AD7879 Touchscreen
Under the device folder there are auxiliary functions such as GPIO and disable controls
root:/> cd sys/class/input/input0/device/ root:/sys/devices/platform/bfin-spi.0/spi0.1> ls -al drwxr-xr-x 3 root root 0 Jan 3 13:02 . drwxr-xr-x 5 root root 0 Jan 3 13:02 .. lrwxrwxrwx 1 root root 0 Jan 3 13:04 bus -> ../../../../bus/spi -rw-rw-r-- 1 root root 4096 Jan 3 13:04 disable lrwxrwxrwx 1 root root 0 Jan 3 13:04 driver -> ../../../../bus/spi/drivers/ad7879 -rw-rw-r-- 1 root root 4096 Jan 3 13:04 gpio lrwxrwxrwx 1 root root 0 Jan 3 13:04 input:input0 -> ../../../../class/input/input0 -r--r--r-- 1 root root 4096 Jan 3 13:04 modalias drwxr-xr-x 2 root root 0 Jan 3 13:04 power lrwxrwxrwx 1 root root 0 Jan 3 13:04 subsystem -> ../../../../bus/spi -rw-r--r-- 1 root root 4096 Jan 3 13:04 uevent root:/sys/devices/platform/bfin-spi.0/spi0.1> cat gpio 0 root:/sys/devices/platform/bfin-spi.0/spi0.1> echo 1 > gpio root:/sys/devices/platform/bfin-spi.0/spi0.1> cat gpio 1 root:/sys/devices/platform/bfin-spi.0/spi0.1>
More Information
Touchscreen calibration
See the uclinux-dist:tslib page for more information.
Using the AD7879 in Microwin / Nano-X
User Configuration
- Enable Microwin during Customize Application/Library Settings
- Manually edit user/microwin/src/config
Enable:
AD7877MOUSE = Y
Disable:
NOMOUSE = N
Testing and Calibration
root:/> nano-X & 210 root:/> nanowm & 211 root:/> nxcal <-- TS Calibration Utility root:/> nxeyes
Nanox with tslib
For kernel after 2.6.22, “/dev/input/ts*” interface has been deprecated in linux. Nanox need to use tslib for touchscreen. To enable:
#################################################################### # Mouse drivers # GPMMOUSE gpm mouse # SERMOUSE serial Microsoft, PC, Logitech, PS/2 mice (/dev/psaux) # SUNMOUSE Sun Workstation mouse (/dev/sunmouse) # NOMOUSE no mouse driver # # Touchscreen drivers # IPAQMOUSE Compaq iPAQ, Intel Assabet (/dev/h3600_tsraw) # ZAURUSMOUSE Sharp Zaurus (/dev/sharp_ts) # TUXMOUSE TuxScreen (/dev/ucb1x00-ts) # ADSMOUSE Applied Data Systems GC+ (/dev/ts) # ADS7846MOUSE ADS7846 chip, PSI OMAP Innovator (/dev/innnovator_ts) # EPMOUSE Embedded Planet (/dev/tpanel) # VHMOUSE Vtech Helio (/dev/tpanel) # MTMOUSE MicroTouch serial (/dev/ttyS1) # PSIONMOUSE Psion 5 (/dev/touch_psion) # YOPYMOUSE Yopy (/dev/yopy-ts) # HARRIERMOUSE NEC Harrier (/dev/tpanel) # AD7877MOUSE Analog Devices AD7877/9 Touch Screen Digitizer (/dev/ts0) # TSLIBMOUSE Common touchscreen driver using tslib #################################################################### GPMMOUSE = N SERMOUSE = N SUNMOUSE = N IPAQMOUSE = N ZAURUSMOUSE = N TUXMOUSE = N ADSMOUSE = N ADS7846MOUSE = N EPMOUSE = N VHMOUSE = N MTMOUSE = N PSIONMOUSE = N YOPYMOUSE = N HARRIERMOUSE = N LIRCMOUSE = N AD7879MOUSE = N TSLIBMOUSE = Y NOMOUSE = N
Before start nano-x, need to set up uclinux-dist:tslib first (including running ts_calibrate):
root:/> . /etc/tslib.env root:/> ts_calibrate root:/> nano-X & root:/> nanowm &
Example Links Graphical Browser
Enable Links
Network Applications [*] links (web browswer)
Start Links
root:/> links -g http://uclinux.org
~~~~~~~~~~~~~~~~~~~~~~~~~~| DirectFB 1.2.3 |~~~~~~~~~~~~~~~~~~~~~~~~~~
(c) 2001-2008 The world wide DirectFB Open Source Community
(c) 2000-2004 Convergence (integrated media) GmbH
----------------------------------------------------------------
(*) DirectFB/Core: Single Application Core. (2008-10-08 07:38)
(*) Direct/Thread: Started 'VT Switcher' (235) [CRITICAL OTHER/OTHER 0/0] <12288>...
(*) Direct/Thread: Started 'Keyboard Input' (236) [INPUT OTHER/OTHER 0/0] <12288>...
(*) DirectFB/Input: Keyboard 0.9 (directfb.org)
(*) Direct/Thread: Started 'tslib Input' (237) [INPUT OTHER/OTHER 0/0] <12288>...
(*) DirectFB/Input: tslib touchscreen 0 0.1 (tslib)
(*) DirectFB/Graphics: Generic Software Rasterizer 0.6 (directfb.org)
(*) DirectFB/Core/WM: Default 0.3 (directfb.org)
(*) FBDev/Surface: Allocated 320x240 16 bit RGB16 buffer (index 0) at offset 0 and pitch 640.
(!) DirectFB/FBDev: Panning display failed (x=0 y=0 ywrap=0 vbl=1)!
--> Invalid argument
Driver Source
Most people should not care about the driver source - it just works as a normal Linux input device. If you are interested, you can look at the driver source at :
<source trunk/drivers/input/touchscreen/ad7879.c:ad7879_report() c linux-kernel>
resources/tools-software/linux-drivers/input-touchscreen/ad7879.txt · Last modified: 11 Feb 2016 21:12 by Lars-Peter Clausen