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Table of Contents
ADXL345 Input 3-Axis Digital Accelerometer Linux Driver
Supported Devices
Reference Circuits
Evaluation Boards
Description
The ADXL345 is a small, thin, ultra low power, 3-axis accelerometer with high resolution (13-bit) measurement up to ±16 g. Digital output data is formatted as 16-bit twos complement and is accessible through either a SPI (3- or 4- wire) or I2C digital interface.
The ADXL345 is well suited for mobile device applications. It measures the static acceleration of gravity in tilt-sensing applications, as well as dynamic acceleration resulting from motion or shock. Its high resolution (4mg/LSB) enables resolution of inclination changes of as little as 0.25°.
Several special sensing functions are provided. Activity and inactivity sensing detect the presence or lack of motion and if the acceleration on any axis exceeds a user-set level. Tap sensing detects single and double taps. Free-Fall sensing detects if the device is falling. These functions can be mapped to interrupt output pins. An integrated 32 level FIFO can be used to store data to minimize host processor intervention.
Low power modes enable intelligent motion-based power management with threshold sensing and active acceleration measurement at extremely low power dissipation.
ADXL345 - Small, Ultra Low Power, 3-Axis, ±2/4/8/16g Digital Accelerometer
ADXL346 - Ultra Low Power, Three-Axis, +-2/4/8/16g Digital Accelerometer
ADXL34x Hardware Features
ADXL345/346:
- Ultra low power
- Power consumption scales automatically with bandwidth
- User selectable fixed 10-bit resolution or 4mg/LSB scale factor in all g-ranges, up to 13-bit resolution at ±16 g
- 32 level output data FIFO minimizes host processor load
- Built in motion detection functions
- Tap/Double Tap detection
- Activity/Inactivity monitoring
- Free-Fall detection
- Supply and I/O voltage range: 1.8 V to 3.6 V (ADXL345) and 1.7 V to 2.75 V (ADXL346)
- SPI (3 and 4 wire) and I2C digital interfaces
- Flexible interrupt modes – Any interrupt mappable to either interrupt pin
- See data sheet for additional features
ADXL346:
- 4- and 6-position orientation sensing
Configuration
Selectable ADXL34X I2C Device Address:
| SDO | I2C Address |
|---|---|
| 0 | 0x53 |
| 1 | 0x1D |
Software configurable features
ADXL34x Linux Driver Features
ADXL345/346:
- Driver supports both SPI (3 and 4 wire) and I2C digital interface
- I2C client using the 2.6 new style binding driver model
- SPI using the generic Linux SPI Bus Driver Model
- Support for Linux Power Management (PM) suspend resume
- User selectable Sample Rate / Bandwidth trough sysfs hooks
- User selectable resolution
- Support for 32 level output data FIFO that minimizes host processor load
- Option to report acceleration as Linux Input Absolute or Relative events. (EV_ABS or EV_REL)
- Motion detection functions
- Tap/Double Tap detection
- User selectable Linux Input Event Codes for TAP_x,y,z axis
- Activity/Inactivity monitoring
- User selectable Linux Input Event Code for Activity/Inactivity reporting
- Option to minimize host processor load and save additional power by automatically switch to sleep mode during periods of inactivity.
- Free-Fall detection
- User selectable Linux Input Event Code for Free-Fall reporting
ADXL346:
- 4- and 6-position orientation sensing
- User selectable Linux Input Event Code for individual positions
Source Code
Status
Status
Files
| Function | File |
|---|---|
| driver | drivers/input/misc/adxl34x.c |
| i2c bus support | drivers/input/misc/adxl34x-i2c.c |
| spi bus support | drivers/input/misc/adxl34x-spi.c |
| include | include/linux/input/adxl34x.h |
ADXL345/6 driver porting
Starting with linux-2.6.36 the ADXL34x driver is mainlined. If you are using an pre linux-2.6.36 kernel get the source from our repositories and add them to your kernel tree.
If you are using a kernel version without the threaded irq capabilities (< 2.6.30) get there driver from here:
-
- Copy to linux-2.6.x/drivers/input/misc/adxl34x.c
-
- Copy to linux-2.6.x/drivers/input/misc/adxl34x.h
-
- Copy to linux-2.6.x/drivers/input/misc/adxl34x-i2c.c
-
- Copy to linux-2.6.x/drivers/input/misc/adxl34x-spi.c
-
- Copy to linux-2.6.x/include/linux/input/adxl34x.h
For the latest version of checkout the Files section of this document.
Add following lines to linux-2.6.x/drivers/input/misc/Kconfig:
config INPUT_ADXL34X tristate "Analog Devices ADXL34x Three-Axis Digital Accelerometer" default n help Say Y here if you have a Accelerometer interface using the ADXL345/6 controller, and your board-specific initialization code includes that in its table of devices. This driver can use either I2C or SPI communication to the ADXL345/6 controller. Select the appropriate method for your system. If unsure, say N (but it's safe to say "Y"). To compile this driver as a module, choose M here: the module will be called adxl34x. config INPUT_ADXL34X_I2C tristate "support I2C bus connection" depends on INPUT_ADXL34X && I2C default y help Say Y here if you have ADXL345/6 hooked to an I2C bus. To compile this driver as a module, choose M here: the module will be called adxl34x-i2c. config INPUT_ADXL34X_SPI tristate "support SPI bus connection" depends on INPUT_ADXL34X && SPI default y help Say Y here if you have ADXL345/6 hooked to a SPI bus. To compile this driver as a module, choose M here: the module will be called adxl34x-spi.
Add following lines to linux-2.6.x/drivers/input/misc/Makefile:
obj-$(CONFIG_INPUT_ADXL34X) += adxl34x.o obj-$(CONFIG_INPUT_ADXL34X_I2C) += adxl34x-i2c.o obj-$(CONFIG_INPUT_ADXL34X_SPI) += adxl34x-spi.o
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.
Digital Accelerometer characteristics are highly application specific and may vary between boards and models. The platform_data for the device's “struct device” holds this information.
<source trunk/include/linux/input/adxl34x.h c linux-kernel>
Example Platfrom / Board file (SPI Interface Option)
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-bf548/boards/ezkit.c:
#include <linux/spi/adxl34x.h>
<source trunk/arch/blackfin/mach-bf548/boards/ezkit.c:adxl34x_info{} c linux-kernel> <source trunk/arch/blackfin/mach-bf548/boards/ezkit.c:spi_adxl34x_chip_info{} c linux-kernel> <source trunk/arch/blackfin/mach-bf548/boards/ezkit.c:bfin_spi_board_info[] c linux-kernel>
Example Platfrom / Board file (I2C Interface Option)
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
These snippets are all from the same file. arch/blackfin/mach-bf548/boards/ezkit.c:
<source trunk/arch/blackfin/mach-bf548/boards/ezkit.c:adxl34x_info{} c linux-kernel> <source trunk/arch/blackfin/mach-bf548/boards/ezkit.c:bfin_i2c_board_info1[] c linux-kernel>
Adding Linux driver support
Configure kernel with “make menuconfig” (alternatively use “make xconfig” or “make qconfig”)
The ADXL34x 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 --->
[*] Miscellaneous devices --->
< > Analog Devices AD714x Capacitance Touch Sensor
<*> Analog Devices ADXL34x Three-Axis Digital Accelerometer
<*> support I2C bus connection (NEW)
<*> support SPI bus connection (NEW)
Hardware I/O ports --->
Hardware configuration
Driver testing
Driver compiled as a module
I2C Interface:
root:~> modprobe evdev root:~> modprobe adxl34x input: ADXL34x accelerometer as /devices/platform/i2c-bfin-twi.1/i2c-adapter/i2c-1/1-0053/input/input1 adxl34x 1-0053: ADXL345 accelerometer, irq 140
SPI Interface:
root:~> modprobe evdev root:~> modprobe adxl34x input: ADXL34x accelerometer as /devices/platform/bfin-spi.1/spi1.2/input/input1 adxl34x spi1.2: ADXL345 accelerometer, irq 140
Driver compiled into the kernel
Your kernel startup messages should include something like this
I2C Interface:
input: ADXL34x accelerometer as /devices/platform/i2c-bfin-twi.1/i2c-adapter/i2c-1/1-0053/input/input1 adxl34x 1-0053: ADXL345 accelerometer, irq 140
SPI Interface:
input: ADXL34x accelerometer as /devices/platform/bfin-spi.1/spi1.2/input/input1 adxl34x spi1.2: ADXL345 accelerometer, irq 140
Common Problems
In case you see a message like this
adxl34x spi1.2: Failed to probe ADXL34x accelerometer
This means that the SPI communication and initilaization with the ADXL34x 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 accelerometer
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 root:/>
Check that the interrupt is registered.
root:~> cat /proc/interrupts | grep adxl34x 140: 0 adxl34x
root:~> cat /sys/class/input/input1/name ADXL34x accelerometer
Use the event_test utility to test proper function
root:/> event_test /dev/input/event1
Input driver version is 1.0.0
Input device ID: bus 0x18 vendor 0x0 product 0x159 version 0x0
Input device name: "ADXL34x accelerometer"
Supported events:
Event type 0 (Reset)
Event code 0 (Reset)
Event code 1 (Key)
Event code 3 (Absolute)
Event type 1 (Key)
Event code 330 (Touch)
Event type 3 (Absolute)
Event code 0 (X)
Value 15
Min -4096
Max 4096
Fuzz 3
Flat 3
Event code 1 (Y)
Value -15
Min -4096
Max 4096
Fuzz 3
Flat 3
Event code 2 (Z)
Value 242
Min -4096
Max 4096
Fuzz 3
Flat 3
Testing ... (interrupt to exit)
Event: time 107831.548000, type 3 (Absolute), code 0 (X), value -7
Event: time 107831.548000, type 3 (Absolute), code 1 (Y), value -2
Event: time 107831.548000, type 3 (Absolute), code 2 (Z), value 12
Event: time 107831.548000, type 0 (Reset), code 0 (Reset), value 0
Event: time 107831.588000, type 3 (Absolute), code 0 (X), value -17
Event: time 107831.588000, type 3 (Absolute), code 1 (Y), value 4
Event: time 107831.588000, type 0 (Reset), code 0 (Reset), value 0
Event: time 107831.632000, type 3 (Absolute), code 0 (X), value -16
Event: time 107831.632000, type 3 (Absolute), code 2 (Z), value 11
In case you move the accelerometer and don't receive events, it's likely that something with your Interrupt is wrong.
check irq number in your platform device file
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
Visualizing Linux Input Events using df_input example from DirectFB
root:/> df_input &
~~~~~~~~~~~~~~~~~~~~~~~~~~| DirectFB 1.2.7 |~~~~~~~~~~~~~~~~~~~~~~~~~~
(c) 2001-2008 The world wide DirectFB Open Source Community
(c) 2000-2004 Convergence (integrated media) GmbH
----------------------------------------------------------------
(*) DirectFB/Core: Single Application Core. (2009-05-27 15:03)
[1] 401 df_input
root:/> (*) Direct/Thread: Started 'VT Switcher' (405) [CRITICAL OTHER/OTHER 0/0] <12288>...
(*) Direct/Thread: Started 'Keyboard Input' (406) [INPUT OTHER/OTHER 0/0] <12288>...
(*) DirectFB/Input: Keyboard 0.9 (directfb.org)
(*) Direct/Thread: Started 'Linux Input' (407) [INPUT OTHER/OTHER 0/0] <12288>...
(*) DirectFB/Input: bf54x-keys (1) 0.1 (directfb.org)
(*) Direct/Thread: Started 'Linux Input' (408) [INPUT OTHER/OTHER 0/0] <12288>...
(*) DirectFB/Input: ADXL34x accelerometer (2) 0.1 (directfb.org)
(*) DirectFB/Graphics: Generic Software Rasterizer 0.6 (directfb.org)
(*) DirectFB/Core/WM: Default 0.3 (directfb.org)
(*) FBDev/Surface: Allocated 480x272 24 bit RGB24 buffer (index 0) at offset 0 and pitch 1440.
(*) FBDev/Surface: Allocated 480x272 24 bit RGB24 buffer (index 0) at offset 0 and pitch 1440.
(*) Direct/Interface: Loaded 'FT2' implementation of 'IDirectFBFont'.
(*) Direct/Interface: Loaded 'PNG' implementation of 'IDirectFBImageProvider'.
root:/>
ADXL34x Sysfs runtime controls
root:/> cd sys/class/input/input1/device/ root:/sys/devices/platform/bfin-spi.1/spi1.2> ls -al drwxr-xr-x 3 root root 0 Jan 2 10:39 . drwxr-xr-x 4 root root 0 Jan 2 10:39 .. -rw-rw-r-- 1 root root 4096 Jan 2 12:01 autosleep -rw-rw-r-- 1 root root 4096 Jan 2 12:01 calibrate -rw-rw-r-- 1 root root 4096 Jan 2 12:01 disable lrwxrwxrwx 1 root root 0 Jan 2 12:01 driver -> ../../../../bus/spi/drivers/adxl34x drwxr-xr-x 3 root root 0 Jan 2 10:39 input -r--r--r-- 1 root root 4096 Jan 2 12:01 modalias -rw-rw-r-- 1 root root 4096 Jan 2 12:01 rate lrwxrwxrwx 1 root root 0 Jan 2 12:01 subsystem -> ../../../../bus/spi -rw-r--r-- 1 root root 4096 Jan 2 12:01 uevent root:/sys/devices/platform/bfin-spi.1/spi1.2>
Device Calibration
root:/sys/devices/platform/bfin-spi.1/spi1.2> echo 1 > calibrate root:/sys/devices/platform/bfin-spi.1/spi1.2> cat calibrate 2,10,-204
Controlling the Output Data Rate
| Output Data Rate (Hz) | Bandwidth (Hz) | Value |
|---|---|---|
| 3200 | 1600 | 15 |
| 1600 | 800 | 14 |
| 800 | 400 | 13 |
| 400 | 200 | 12 |
| 200 | 100 | 11 |
| 100 | 50 | 10 |
| 50 | 25 | 9 |
| 25 | 12.5 | 8 |
| 12.5 | 6.25 | 7 |
| 6.25 | 3.125 | 6 |
| 3.125 | 1.563 | 5 |
| 1.563 | 0.782 | 4 |
| 0.782 | 0.39 | 3 |
| 0.39 | 0.195 | 2 |
| 0.195 | 0.098 | 1 |
| 0.098 | 0.048 | 0 |
Writing 'value' into rate sets the desired sample rate
Reading rate returns the current value
See table above for supported sample rates
root:/sys/devices/platform/bfin-spi.1/spi1.2> echo 8 > rate root:/sys/devices/platform/bfin-spi.1/spi1.2> cat rate 8
Be aware:
The ADXL34x conforms to The I2C Bus Specification, Version 2.1,
January 2000, available from Phillips Semiconductor. It
supports standard (100 kHz) and fast (400 kHz) data transfer modes.
Very high output data rates are only possible via fast I2C (400kHz) or the SPI interface.
Enabling / Disabling the Device
Writing '1' into disable - disables the ADXL34x (low power suspend mode)
Writing '0' into disable - enables the ADXL34x
root:/sys/devices/platform/bfin-spi.1/spi1.2> echo 1 > disable root:/sys/devices/platform/bfin-spi.1/spi1.2> echo 0 > disable root:/sys/devices/platform/bfin-spi.1/spi1.2>
Enabling / Disabling Autosleep Upon Inactivity
Writing '1' into autosleep - enables Autosleep Upon Inactivity
Writing '0' into autosleep - disables Autosleep Upon Inactivity
root:/sys/devices/platform/bfin-spi.1/spi1.2> echo 1 > autosleep root:/sys/devices/platform/bfin-spi.1/spi1.2> echo 0 > autosleep root:/sys/devices/platform/bfin-spi.1/spi1.2>
More Information
ADXL345/6 Android Acceleration Sensor
Using this driver under Android as Acceleration Sensor Follow the link here ADXL345 Android Sensor
resources/tools-software/linux-drivers/input-misc/adxl345.1328002655.txt.gz · Last modified: 31 Jan 2012 10:37 (external edit)