drivers/staging/iio/imu/inv_mpu/README - kernel/tegra.git - Git at Google

 Kernel driver inv-mpu-iio
 Author: Invensense <http://invensense.com>

 Table of Contents:
 ==================
 - Description
 - Integrating the Driver in the Linux Kernel
 - Board and Platform Data
     > Interrupt Pin
     > Platform Data
 - Board File Modifications for Secondary I2C Configuration
     > MPU-6050 + AKM8963 on the secondary I2C interface
     > MPU-6500 + AKM8963 on the secondary I2C interface
     > MPU-9150
     > MPU-3050 + BMA250 on the secondary I2C interface
 - Board File Modifications for Invensense Devices
     > MPU-3050
     > ITG-3500
     > MPU-6050
     > MPU-6500
     > MPU-9150
 - IIO Subsystem
     > Communicating with the Driver in Userspace
     > ITG-3500
     > MPU-6050 and MPU-6500
     > MPU-9150
     > MPU-3050 + BMA250 on the secondary I2C interface
 - Low Power Accelerometer Mode
 - DMP Event
 - Streaming Data to an Userspace Application
 - Recommended Sysfs Entry Setup Sequence
     > With DMP Firmware
     > Without DMP Firmware
 - Test Applications
     > Running Test Applications with MPU-9150/MPU-6050/MPU-6500
     > Running Test Applications with MPU-3050/ITG-3500


 Description
 ===========
 This document describes how to install the Invensense device driver into a
 Linux kernel. The Invensense driver currently supports the following sensors:
 - ITG-3500
 - MPU-6050
 - MPU-9150
 - MPU-6500
 - MPU-3050

 The slave address of each device is either 0x68 or 0x69, depending on the AD0
 pin value of the device. Please refer to the appropriate product specification
 document for further information regarding the AD0 pin. The driver supports both
 addresses.

 The following files are included in this package:
 - Kconfig
 - Makefile
 - inv_mpu_core.c
 - inv_mpu_misc.c
 - inv_mpu_trigger.c
 - inv_mpu3050_iio.c
 - inv_mpu_iio.h
 - inv_mpu_ring.c
 - inv_slave_bma250.c
 - dmpDefaultMPU6050.c
 - dmpkey.h
 - dmpmap.h
 - mpu.h


 Integrating the Driver in the Linux Kernel
 ==========================================
 Please add the files as follows:
 - Add mpu.h to "kernel/include/linux".
 - Add all other files to drivers/staging/iio/imu/mpu
 (another directory is acceptable, but this is the recommended destination)

 In order to see the driver in menuconfig when building the kernel, please
 make modifications as shown below:

     modify "drivers/staging/iio/imu/Kconfig" with:
     >> source "drivers/staging/iio/imu/mpu/Kconfig"

     modify "drivers/staging/iio/imu/Makefile" with:
     >> obj-y += mpu/


 Board and Platform Data
 =======================
 In order to recognize the Invensense device on the I2C bus, the board file must
 be modified.
 The i2c_board_info instance must be defined as shown below.

 Interrupt Pin
 -------------
 The hardcoded value of 140 corresponds to the GPIO input pin connected to the
 Invensense device's interrupt pin.
 This pin will most likely be different for your platform, and the value should
 be changed accordingly.

 Platform Data
 -------------
 The platform data (orientation matrix and secondary bus configurations) must be
 modified as show below, according to your particular platform configuration.

 Please note that the MPU-9150 it is treated as a MPU-6050 with AKM8975 on the
 device's secondary I2C interface. Thus the secondary I2C address must be
 provided.


 Board File Modifications for Secondary I2C Configuration
 ========================================================
 For the Panda Board, the board file can be found at
 arch/arm/mach-omap2/board-omap4panda.c.
 Please modify the pertinent baord file in your system according to the examples
 shown below:

 MPU-6050 + AKM8963 on the secondary I2C interface
 -------------------------------------------------
 static struct mpu_platform_data gyro_platform_data = {
 	.int_config  = 0x10,
 	.level_shifter = 0,
 	.orientation = {  -1,  0,  0,
 			   0,  1,  0,
 			   0,  0, -1 },
 	.sec_slave_type = SECONDARY_SLAVE_TYPE_COMPASS,
 	.sec_slave_id   = COMPASS_ID_AK8963,
 	.secondary_i2c_addr = 0x0E
 };

 MPU-6500 + AKM8963 on the secondary I2C interface
 -------------------------------------------------
 static struct mpu_platform_data gyro_platform_data = {
         .int_config  = 0x10,
         .level_shifter = 0,
         .orientation = {  -1,  0,  0,
                            0,  1,  0,
                            0,  0, -1 },
         .sec_slave_type = SECONDARY_SLAVE_TYPE_COMPASS,
         .sec_slave_id   = COMPASS_ID_AK8963,
         .secondary_i2c_addr = 0x0E
 };

 MPU-9150
 --------
 For MPU-9150, please provide the following secondary I2C bus information.

 static struct mpu_platform_data gyro_platform_data = {
 	.int_config  = 0x10,
 	.level_shifter = 0,
 	.orientation = {  -1,  0,  0,
 			   0,  1,  0,
 			   0,  0, -1 },
 	.sec_slave_type = SECONDARY_SLAVE_TYPE_COMPASS,
 	.sec_slave_id   = COMPASS_ID_AK8975,
 	.secondary_i2c_addr = 0x0E
 };

 MPU-3050 + BMA250 on the secondary I2C interface
 ------------------------------------------------
 For BMA250 on the secondary I2C bus, please provide the following information.

 static struct mpu_platform_data gyro_platform_data = {
 	.int_config  = 0x10,
 	.level_shifter = 0,
 	.orientation = {  -1,  0,  0,
 			   0,  1,  0,
 			   0,  0, -1 },
 	.sec_slave_type = SECONDARY_SLAVE_TYPE_ACCEL,
 	.sec_slave_id   = ACCEL_ID_BMA250,
 	.secondary_i2c_addr = 0x18,
 };


 Board File Modifications for Invensense Devices
 ===============================================
 For Invensense devices, please provide the i2c init data as shown in the
 examples below.

 In the _i2c_init function, the device is registered in the following manner:

     // arch/arm/mach-omap2/board-omap4panda.c
     // in static int __init omap4_panda_i2c_init(void)
     omap_register_i2c_bus(4, 400,
                           single_chip_board_info,
                           ARRAY_SIZE(single_chip_board_info));

 MPU-3050
 --------
 static struct i2c_board_info __initdata single_chip_board_info[] = {
 	{
 		I2C_BOARD_INFO("mpu3050", 0x68),
 		.irq = (IH_GPIO_BASE + MPUIRQ_GPIO),
 		.platform_data = &gyro_platform_data,
 	},
 };

 ITG-3050
 --------
 static struct i2c_board_info __initdata single_chip_board_info[] = {
 	{
 		I2C_BOARD_INFO("itg3500", 0x68),
 		.irq = (IH_GPIO_BASE + MPUIRQ_GPIO),
                 .platform_data = &gyro_platform_data,
 	},
 };

 MPU6050
 -------
 static struct i2c_board_info __initdata single_chip_board_info[] = {
 	{
 		I2C_BOARD_INFO("mpu6050", 0x68),
 		.irq = (IH_GPIO_BASE + MPUIRQ_GPIO),
 		.platform_data = &gyro_platform_data,
 	},
 };

 MPU6500
 -------
 static struct i2c_board_info __initdata single_chip_board_info[] = {
         {
                 I2C_BOARD_INFO("mpu6500", 0x68),
                 .irq = (IH_GPIO_BASE + MPUIRQ_GPIO),
                 .platform_data = &gyro_platform_data,
         },
 };

 MPU9150
 -------
 arch/arm/mach-omap2/board-omap4panda.c
 static struct i2c_board_info __initdata single_chip_board_info[] = {
 	{
 		I2C_BOARD_INFO("mpu9150", 0x68),
 		.irq = (IH_GPIO_BASE + MPUIRQ_GPIO),
 		.platform_data = &gyro_platform_data,
 	},
 };


 IIO subsystem
 =============
 A successful installation will create the following two new directories under
 /sys/bus/iio/devices:
     - iio:device0
     - trigger0

 Also, a new file, "iio:device0", will be created in the /dev/ diretory.
 (if you have more than one IIO device, the file will be named "iio:deviceX",
 where X is a number)


 Communicating with the Driver in Userspace
 ------------------------------------------
 The driver generates several files in sysfs upon installation.
 These files are used to communicate with the driver. The files can be found
 at /sys/bus/iio/devices/iio:device0 (or ../iio:deviceX as shown above).

 A brief description of the pertinent files for each Invensense device is shown
 below:

 ITG-3500
 --------
 temperature (Read-only)
 --Read temperature data directly from the temperature register.

 sampling_frequency (Read/write)
 --Configure the ADC sampling rate and FIFO output rate.

 sampling_frequency_available(read-only)
 --show commonly used frequency

 clock_source (Read-only)
 --Check which clock-source is used by the chip.

 power_state (Read/write)
 --turn on/off the power supply

 self_test (read-only)
 --read this entry trigger self test. The return value is D.
 D is the success/fail.
 For different chip, the result is different for success/fail.
 1 means success 0 means fail. The LSB of D is for gyro; the bit
 next to LSB of D is for accel. The bit 2 of D is for compass result.

 key (read-only)
 --show the key value of this driver. Used by MPL.

 gyro_matrix (read-only)
 --show the orientation matrix obtained from the board file.

 MPU-6050 and MPU-6500
 ---------------------
 MPU-6050 and MPU-6500 have all sysfs files belonging to ITG-3500 (shown above).
 In addition, it has the files below:

 gyro_enable (read/write)
 --enable/disable gyro functionality. Affects raw_gyro. Turning this off this
   will shut down gyro and save power.

 accl_enable (read/write)
 --enable/disable accelerometer functionality. Affects raw_accl.
 Turning this off this will shut down accel and save power.

 firmware_loaded (read/write)
 --Flag indicating the whether firmware is loaded or not in the DMP engine.
 0 means no firmware loaded. 1 means firmware is already loaded . This
 flag can only be written as 0. It internally updates to 1.

 dmp_on(read/write)
 --This entry controls whether to run DMP or not.
 Write 1 to enable DMP and write 0 to disable dmp.
 Please note that firmware_loaded must be 1 in order to enable DMP.

 dmp_int_on(read/write)
 --This entry controls whether dmp interrupt is on/off.
 Please note that firmware_loaded must be 1.
 Also, we'd like to remind you that it is sometimes advantageous to
 turn interrupts off while the DMP is running.

 dmp_output_rate
 --control dmp output rate when dmp is on.

 dmp_event_int_on(read/write)
 --This entry controls whether dmp event interrupt is on/off.
 Please note that turning this on will turn off the data interrupt.
 Interrupts will be generated only when events occur.
 This is useful for saving power when the system is waiting for a special event
 to wake up.

 dmp_firmware (write only binary file)
 --DMP firmware code is loaded into this entry.
 If loading is successful, the firmware_loaded flag will be updated to 1.
 In order to load new firmware, the firmware_loaded flag must be first set to 0.

 lpa_mode(read-write)
 --Low power accelerometer mode

 lpa_freq(read-write)
 --Low power acceleromter frequency.

 accel_matrix
 --orientation matrix for accelerometer.

 pedometer_time
 pedometer_steps,
 --Pedometer related entries

 event_tap
 event_orientation
 event_display_orientation
 --Event related entries.
 Please poll these entries to read their values. Direct reads will yield
 meaningless results.
 Further details are provided in the DMP Events section of this README.

 tap_on
 --Controls tap function of DMP

 tap_time
 tap_min_count
 tap_threshold
 --Tap related entries. Controls various parameters of tap function.

 orientation_on
 --Turn on/off orientation function of DMP.

 display_orientation_on
 --Turn on/off display orientation function of DMP.

 quaternion_on
 --Turn on/off quaterniion data output. DMP is required for this feature.

 MPU-9150
 --------
 MPU-9150 has all of MPU-6050's entries. It also has two additional entries,
 described below.

 compass_enable (read/write)
 --Enables compass function.

 compass_matrix (read-only)
 --Compass orientation matrix

 MPU-3050 with BMA250 on secondary I2C interface
 -----------------------------------------------
 MPU-3050 with BMA250 on the secondary I2C interface has ever ITG-3500 entry.
 It also has two additional entries, shown below:

 accl_matrix

 accl_enable


 Low Power Accelerometer Mode
 ============================
 Lower power accelerometer mode is a special mode that is only available
 in MPU-6050, MPU-6500, and MPU-9150.

 Only accelerometer is functional in this mode.
 "gyro_enable" and "compass_enable" must be zero. "dmp_on" must be zero.

 Low power acceleromter mode has two entries: lpa_mode and lpa_freq

 To run low power accel mode, set lpa_mode to 1.

 For MPU6050/MPU9150:
 Set lpa_freq to 0~3, which correspond to 1.25Hz, 5Hz, 20Hz, 40Hz.

 For MPU6500:
 Set lpa_freq to 0~11, which correspond to 0.3125Hz to 640Hz.


 DMP Event
 =========
 A DMP Event is an event that is output by the DMP unit within the Invensense
 device (MPU).
 Only the MPU-6050, MPU-6500, and MPU-9150 feature the DMP.


 There are four sysfs entries for DMP events:

 - event_tap
 - event_orientation
 - event_display_orientation

 These four events must be polled before reading.

 The proper method to poll sysfs is as follows:
 1. open file.
 2. dummy read.
 3. poll.
 4. once the poll passed, use fopen and fread to read the sysfs entry.
 5. interpret the data.


 Streaming Data to an Userspace Application
 ==========================================
 When streaming data to an userspace application, we recommend that you access
 gyro/accel/compass data via /dev/iio:device0.

 Please follow the steps below to read data at a constant rate from the driver:

 1. Write a 1 to power_state to turn on the chip. This is the default setting
    after installing the driver.
 2. Write the desired output rate to fifo_rate.
 3. Write 1 to enable to turn on the event.
 4. Read /dev/iio:device0 to get a string of gyro/accel/compass data.
 5. Parse this string to obtain each gyro/accel/compass element.
 6. If dmp firmware code is loaded, use "dmp_on" to enable/disable dmp.
 7. If compass is enabled, the output will contain compass data.


 Recommended Sysfs Entry Setup Senquence
 =======================================

 Without DMP Firmware
 --------------------
 1. Set "power_state" to 1,
 2. Set the scale and fifo rate values according to your needs.
 3. Set gyro_enable, accel_enable, and compass_enable according to your needs.
    For example:
     - If you only want gyro data, set accel_enable to 0 (and compass_enable to
       0, if applicable).
     - If you only want accel data, set gyro_enable to 0 (and compass_enable to
       0, if applicable).
     - If you only want compass data, set gyro_enable to 0 and accel_enable to 0.
 4. Set "enable" to 1.
 5. You will now get the output that you want.

 With DMP Firmware
 -----------------
 1. Set "power_state" to 1.
 2. Write "0" to firmware_loaded if it is not zero already.
 3. Load firmware into "dmp_firmware" as a whole. Don't split the DMP firmware
    image.
 4. Make sure firmware_loaded is 1 after loading the DMP image.
 5. Make appropriate configurations as shown above in the "without DMP firmware"
    case.
 6. Set dmp_on to 1.
 7. Set "enable" to 1.

 Please note that the enable function uses the enable entry under
 "/sys/bus/iio/devices/iio:device0/buffer"

 Test Applications
 =================
 A test application is located under software/simple_apps/mpu_iio.
 This application is stand-alone in that it cannot be run concurrently with other
 entities trying to access the device node(s) or sysfs entries; in particular,
 the

 Running Test Applications with MPU-9150/MPU-6050/MPU-6500
 ---------------------------------------------------------
 To run test applications with MPU-9150, MPU-6050, or MPU-6500 devices,
 please use the following commands:

 1. For orientation/tap/display orientation events:
    mpu_iio -c 10 -l 3 -p

 2. For printing data normally:
    mpu_iio -c 10 -l 3 -r

 Running Test Applications with MPU-3050/ITG-3500
 ------------------------------------------------
 To run test applications with MPU-3050 or ITG-3500 devices,
 please use the following command:

 1. For printing data normally:
    mpu_iio -c 10 -l 3 -r

 Please use mpu_iio.c and iio_utils.h as example code for your development
 purposes.
	Kernel driver inv-mpu-iio
	Author: Invensense <http://invensense.com>

	Table of Contents:
	==================
	- Description
	- Integrating the Driver in the Linux Kernel
	- Board and Platform Data
	> Interrupt Pin
	> Platform Data
	- Board File Modifications for Secondary I2C Configuration
	> MPU-6050 + AKM8963 on the secondary I2C interface
	> MPU-6500 + AKM8963 on the secondary I2C interface
	> MPU-9150
	> MPU-3050 + BMA250 on the secondary I2C interface
	- Board File Modifications for Invensense Devices
	> MPU-3050
	> ITG-3500
	> MPU-6050
	> MPU-6500
	> MPU-9150
	- IIO Subsystem
	> Communicating with the Driver in Userspace
	> ITG-3500
	> MPU-6050 and MPU-6500
	> MPU-9150
	> MPU-3050 + BMA250 on the secondary I2C interface
	- Low Power Accelerometer Mode
	- DMP Event
	- Streaming Data to an Userspace Application
	- Recommended Sysfs Entry Setup Sequence
	> With DMP Firmware
	> Without DMP Firmware
	- Test Applications
	> Running Test Applications with MPU-9150/MPU-6050/MPU-6500
	> Running Test Applications with MPU-3050/ITG-3500



	Description
	===========
	This document describes how to install the Invensense device driver into a
	Linux kernel. The Invensense driver currently supports the following sensors:
	- ITG-3500
	- MPU-6050
	- MPU-9150
	- MPU-6500
	- MPU-3050

	The slave address of each device is either 0x68 or 0x69, depending on the AD0
	pin value of the device. Please refer to the appropriate product specification
	document for further information regarding the AD0 pin. The driver supports both
	addresses.

	The following files are included in this package:
	- Kconfig
	- Makefile
	- inv_mpu_core.c
	- inv_mpu_misc.c
	- inv_mpu_trigger.c
	- inv_mpu3050_iio.c
	- inv_mpu_iio.h
	- inv_mpu_ring.c
	- inv_slave_bma250.c
	- dmpDefaultMPU6050.c
	- dmpkey.h
	- dmpmap.h
	- mpu.h


	Integrating the Driver in the Linux Kernel
	==========================================
	Please add the files as follows:
	- Add mpu.h to "kernel/include/linux".
	- Add all other files to drivers/staging/iio/imu/mpu
	(another directory is acceptable, but this is the recommended destination)

	In order to see the driver in menuconfig when building the kernel, please
	make modifications as shown below:

	modify "drivers/staging/iio/imu/Kconfig" with:
	>> source "drivers/staging/iio/imu/mpu/Kconfig"

	modify "drivers/staging/iio/imu/Makefile" with:
	>> obj-y += mpu/


	Board and Platform Data
	=======================
	In order to recognize the Invensense device on the I2C bus, the board file must
	be modified.
	The i2c_board_info instance must be defined as shown below.

	Interrupt Pin
	-------------
	The hardcoded value of 140 corresponds to the GPIO input pin connected to the
	Invensense device's interrupt pin.
	This pin will most likely be different for your platform, and the value should
	be changed accordingly.

	Platform Data
	-------------
	The platform data (orientation matrix and secondary bus configurations) must be
	modified as show below, according to your particular platform configuration.

	Please note that the MPU-9150 it is treated as a MPU-6050 with AKM8975 on the
	device's secondary I2C interface. Thus the secondary I2C address must be
	provided.


	Board File Modifications for Secondary I2C Configuration
	========================================================
	For the Panda Board, the board file can be found at
	arch/arm/mach-omap2/board-omap4panda.c.
	Please modify the pertinent baord file in your system according to the examples
	shown below:

	MPU-6050 + AKM8963 on the secondary I2C interface
	-------------------------------------------------
	static struct mpu_platform_data gyro_platform_data = {
	.int_config = 0x10,
	.level_shifter = 0,
	.orientation = { -1, 0, 0,
	0, 1, 0,
	0, 0, -1 },
	.sec_slave_type = SECONDARY_SLAVE_TYPE_COMPASS,
	.sec_slave_id = COMPASS_ID_AK8963,
	.secondary_i2c_addr = 0x0E
	};

	MPU-6500 + AKM8963 on the secondary I2C interface
	-------------------------------------------------
	static struct mpu_platform_data gyro_platform_data = {
	.int_config = 0x10,
	.level_shifter = 0,
	.orientation = { -1, 0, 0,
	0, 1, 0,
	0, 0, -1 },
	.sec_slave_type = SECONDARY_SLAVE_TYPE_COMPASS,
	.sec_slave_id = COMPASS_ID_AK8963,
	.secondary_i2c_addr = 0x0E
	};

	MPU-9150
	--------
	For MPU-9150, please provide the following secondary I2C bus information.

	static struct mpu_platform_data gyro_platform_data = {
	.int_config = 0x10,
	.level_shifter = 0,
	.orientation = { -1, 0, 0,
	0, 1, 0,
	0, 0, -1 },
	.sec_slave_type = SECONDARY_SLAVE_TYPE_COMPASS,
	.sec_slave_id = COMPASS_ID_AK8975,
	.secondary_i2c_addr = 0x0E
	};

	MPU-3050 + BMA250 on the secondary I2C interface
	------------------------------------------------
	For BMA250 on the secondary I2C bus, please provide the following information.

	static struct mpu_platform_data gyro_platform_data = {
	.int_config = 0x10,
	.level_shifter = 0,
	.orientation = { -1, 0, 0,
	0, 1, 0,
	0, 0, -1 },
	.sec_slave_type = SECONDARY_SLAVE_TYPE_ACCEL,
	.sec_slave_id = ACCEL_ID_BMA250,
	.secondary_i2c_addr = 0x18,
	};


	Board File Modifications for Invensense Devices
	===============================================
	For Invensense devices, please provide the i2c init data as shown in the
	examples below.

	In the _i2c_init function, the device is registered in the following manner:

	// arch/arm/mach-omap2/board-omap4panda.c
	// in static int __init omap4_panda_i2c_init(void)
	omap_register_i2c_bus(4, 400,
	single_chip_board_info,
	ARRAY_SIZE(single_chip_board_info));

	MPU-3050
	--------
	static struct i2c_board_info __initdata single_chip_board_info[] = {
	{
	I2C_BOARD_INFO("mpu3050", 0x68),
	.irq = (IH_GPIO_BASE + MPUIRQ_GPIO),
	.platform_data = &gyro_platform_data,
	},
	};

	ITG-3050
	--------
	static struct i2c_board_info __initdata single_chip_board_info[] = {
	{
	I2C_BOARD_INFO("itg3500", 0x68),
	.irq = (IH_GPIO_BASE + MPUIRQ_GPIO),
	.platform_data = &gyro_platform_data,
	},
	};

	MPU6050
	-------
	static struct i2c_board_info __initdata single_chip_board_info[] = {
	{
	I2C_BOARD_INFO("mpu6050", 0x68),
	.irq = (IH_GPIO_BASE + MPUIRQ_GPIO),
	.platform_data = &gyro_platform_data,
	},
	};

	MPU6500
	-------
	static struct i2c_board_info __initdata single_chip_board_info[] = {
	{
	I2C_BOARD_INFO("mpu6500", 0x68),
	.irq = (IH_GPIO_BASE + MPUIRQ_GPIO),
	.platform_data = &gyro_platform_data,
	},
	};

	MPU9150
	-------
	arch/arm/mach-omap2/board-omap4panda.c
	static struct i2c_board_info __initdata single_chip_board_info[] = {
	{
	I2C_BOARD_INFO("mpu9150", 0x68),
	.irq = (IH_GPIO_BASE + MPUIRQ_GPIO),
	.platform_data = &gyro_platform_data,
	},
	};


	IIO subsystem
	=============
	A successful installation will create the following two new directories under
	/sys/bus/iio/devices:
	- iio:device0
	- trigger0

	Also, a new file, "iio:device0", will be created in the /dev/ diretory.
	(if you have more than one IIO device, the file will be named "iio:deviceX",
	where X is a number)


	Communicating with the Driver in Userspace
	------------------------------------------
	The driver generates several files in sysfs upon installation.
	These files are used to communicate with the driver. The files can be found
	at /sys/bus/iio/devices/iio:device0 (or ../iio:deviceX as shown above).

	A brief description of the pertinent files for each Invensense device is shown
	below:

	ITG-3500
	--------
	temperature (Read-only)
	--Read temperature data directly from the temperature register.

	sampling_frequency (Read/write)
	--Configure the ADC sampling rate and FIFO output rate.

	sampling_frequency_available(read-only)
	--show commonly used frequency

	clock_source (Read-only)
	--Check which clock-source is used by the chip.

	power_state (Read/write)
	--turn on/off the power supply

	self_test (read-only)
	--read this entry trigger self test. The return value is D.
	D is the success/fail.
	For different chip, the result is different for success/fail.
	1 means success 0 means fail. The LSB of D is for gyro; the bit
	next to LSB of D is for accel. The bit 2 of D is for compass result.

	key (read-only)
	--show the key value of this driver. Used by MPL.

	gyro_matrix (read-only)
	--show the orientation matrix obtained from the board file.

	MPU-6050 and MPU-6500
	---------------------
	MPU-6050 and MPU-6500 have all sysfs files belonging to ITG-3500 (shown above).
	In addition, it has the files below:

	gyro_enable (read/write)
	--enable/disable gyro functionality. Affects raw_gyro. Turning this off this
	will shut down gyro and save power.

	accl_enable (read/write)
	--enable/disable accelerometer functionality. Affects raw_accl.
	Turning this off this will shut down accel and save power.

	firmware_loaded (read/write)
	--Flag indicating the whether firmware is loaded or not in the DMP engine.
	0 means no firmware loaded. 1 means firmware is already loaded . This
	flag can only be written as 0. It internally updates to 1.

	dmp_on(read/write)
	--This entry controls whether to run DMP or not.
	Write 1 to enable DMP and write 0 to disable dmp.
	Please note that firmware_loaded must be 1 in order to enable DMP.

	dmp_int_on(read/write)
	--This entry controls whether dmp interrupt is on/off.
	Please note that firmware_loaded must be 1.
	Also, we'd like to remind you that it is sometimes advantageous to
	turn interrupts off while the DMP is running.

	dmp_output_rate
	--control dmp output rate when dmp is on.

	dmp_event_int_on(read/write)
	--This entry controls whether dmp event interrupt is on/off.
	Please note that turning this on will turn off the data interrupt.
	Interrupts will be generated only when events occur.
	This is useful for saving power when the system is waiting for a special event
	to wake up.

	dmp_firmware (write only binary file)
	--DMP firmware code is loaded into this entry.
	If loading is successful, the firmware_loaded flag will be updated to 1.
	In order to load new firmware, the firmware_loaded flag must be first set to 0.

	lpa_mode(read-write)
	--Low power accelerometer mode

	lpa_freq(read-write)
	--Low power acceleromter frequency.

	accel_matrix
	--orientation matrix for accelerometer.

	pedometer_time
	pedometer_steps,
	--Pedometer related entries

	event_tap
	event_orientation
	event_display_orientation
	--Event related entries.
	Please poll these entries to read their values. Direct reads will yield
	meaningless results.
	Further details are provided in the DMP Events section of this README.

	tap_on
	--Controls tap function of DMP

	tap_time
	tap_min_count
	tap_threshold
	--Tap related entries. Controls various parameters of tap function.

	orientation_on
	--Turn on/off orientation function of DMP.

	display_orientation_on
	--Turn on/off display orientation function of DMP.

	quaternion_on
	--Turn on/off quaterniion data output. DMP is required for this feature.

	MPU-9150
	--------
	MPU-9150 has all of MPU-6050's entries. It also has two additional entries,
	described below.

	compass_enable (read/write)
	--Enables compass function.

	compass_matrix (read-only)
	--Compass orientation matrix

	MPU-3050 with BMA250 on secondary I2C interface
	-----------------------------------------------
	MPU-3050 with BMA250 on the secondary I2C interface has ever ITG-3500 entry.
	It also has two additional entries, shown below:

	accl_matrix

	accl_enable


	Low Power Accelerometer Mode
	============================
	Lower power accelerometer mode is a special mode that is only available
	in MPU-6050, MPU-6500, and MPU-9150.

	Only accelerometer is functional in this mode.
	"gyro_enable" and "compass_enable" must be zero. "dmp_on" must be zero.

	Low power acceleromter mode has two entries: lpa_mode and lpa_freq

	To run low power accel mode, set lpa_mode to 1.

	For MPU6050/MPU9150:
	Set lpa_freq to 0~3, which correspond to 1.25Hz, 5Hz, 20Hz, 40Hz.

	For MPU6500:
	Set lpa_freq to 0~11, which correspond to 0.3125Hz to 640Hz.


	DMP Event
	=========
	A DMP Event is an event that is output by the DMP unit within the Invensense
	device (MPU).
	Only the MPU-6050, MPU-6500, and MPU-9150 feature the DMP.


	There are four sysfs entries for DMP events:

	- event_tap
	- event_orientation
	- event_display_orientation

	These four events must be polled before reading.

	The proper method to poll sysfs is as follows:
	1. open file.
	2. dummy read.
	3. poll.
	4. once the poll passed, use fopen and fread to read the sysfs entry.
	5. interpret the data.


	Streaming Data to an Userspace Application
	==========================================
	When streaming data to an userspace application, we recommend that you access
	gyro/accel/compass data via /dev/iio:device0.

	Please follow the steps below to read data at a constant rate from the driver:

	1. Write a 1 to power_state to turn on the chip. This is the default setting
	after installing the driver.
	2. Write the desired output rate to fifo_rate.
	3. Write 1 to enable to turn on the event.
	4. Read /dev/iio:device0 to get a string of gyro/accel/compass data.
	5. Parse this string to obtain each gyro/accel/compass element.
	6. If dmp firmware code is loaded, use "dmp_on" to enable/disable dmp.
	7. If compass is enabled, the output will contain compass data.


	Recommended Sysfs Entry Setup Senquence
	=======================================

	Without DMP Firmware
	--------------------
	1. Set "power_state" to 1,
	2. Set the scale and fifo rate values according to your needs.
	3. Set gyro_enable, accel_enable, and compass_enable according to your needs.
	For example:
	- If you only want gyro data, set accel_enable to 0 (and compass_enable to
	0, if applicable).
	- If you only want accel data, set gyro_enable to 0 (and compass_enable to
	0, if applicable).
	- If you only want compass data, set gyro_enable to 0 and accel_enable to 0.
	4. Set "enable" to 1.
	5. You will now get the output that you want.

	With DMP Firmware
	-----------------
	1. Set "power_state" to 1.
	2. Write "0" to firmware_loaded if it is not zero already.
	3. Load firmware into "dmp_firmware" as a whole. Don't split the DMP firmware
	image.
	4. Make sure firmware_loaded is 1 after loading the DMP image.
	5. Make appropriate configurations as shown above in the "without DMP firmware"
	case.
	6. Set dmp_on to 1.
	7. Set "enable" to 1.

	Please note that the enable function uses the enable entry under
	"/sys/bus/iio/devices/iio:device0/buffer"

	Test Applications
	=================
	A test application is located under software/simple_apps/mpu_iio.
	This application is stand-alone in that it cannot be run concurrently with other
	entities trying to access the device node(s) or sysfs entries; in particular,
	the

	Running Test Applications with MPU-9150/MPU-6050/MPU-6500
	---------------------------------------------------------
	To run test applications with MPU-9150, MPU-6050, or MPU-6500 devices,
	please use the following commands:

	1. For orientation/tap/display orientation events:
	mpu_iio -c 10 -l 3 -p

	2. For printing data normally:
	mpu_iio -c 10 -l 3 -r

	Running Test Applications with MPU-3050/ITG-3500
	------------------------------------------------
	To run test applications with MPU-3050 or ITG-3500 devices,
	please use the following command:

	1. For printing data normally:
	mpu_iio -c 10 -l 3 -r

	Please use mpu_iio.c and iio_utils.h as example code for your development
	purposes.