• AD7879
• AD7879-1
• AD7889
• AD7889-1

• EVAL-AD7879EBZ
• EVAL-AD7879-1EBZ

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

AD7879-1/AD7889-1 I2C Device Address options:

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

Touchscreen characteristics vary between boards and models. The platform_data for the device's “struct device” holds this information.

These snippets are all from the same file. arch/blackfin/mach-bf537/boards/stamp.c:

#include 
 
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
};

#include 
 
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
}

Configure kernel with “make menuconfig” (alternatively use “make xconfig” or “make qconfig”)

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  --->

root:~> modprobe evdev
root:~> modprobe ad7879
input: AD7879 Touchscreen as /class/input/input0
ad7879 spi0.1: touchscreen, irq 57

Your kernel startup messages should include something like this

input: AD7879 Touchscreen as /class/input/input0
ad7879 spi0.1: touchscreen, irq 57

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

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

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 ------------

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:/>

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

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>

See the uclinux-dist:tslib page for more information.

• Enable Microwin during Customize Application/Library Settings
• Manually edit user/microwin/src/config

Enable:
AD7877MOUSE = Y

Disable:
NOMOUSE = N

root:/> nano-X &
210
root:/> nanowm &
211
root:/> nxcal <-- TS Calibration Utility
root:/> nxeyes

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 &

uclinux-dist:browsers

Network Applications
	[*] links (web browswer)

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

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 :