tegrakernel/kernel/kernel-4.9/drivers/iio/magnetometer/inv_compass

Kernel driver
Author: Invensense <http://invensense.com>

Table of Contents:
==================
- Description
- Integrating the Driver in the Linux Kernel
- Board and Platform Data
    > Platform Data
- Board File Modifications for compass
    > AMI306
    > YAS530/532/533
- IIO Subsystem
    > Communicating with the Driver in Userspace
- Streaming Data to an Userspace Application
- Test Applications
    > Running Test Applications with AMI306 or YAS53x

Description
===========
This document describes how to install the Invensense device driver for AMI306
and YAS53x series compass chip into a Linux kernel. The Invensense driver
currently supports the following sensors:
- AMI306
- YAS530
- YAS532
- YAS533

Please refer to the appropriate product specification
document for further information regarding the slave address.

The following files are included in this package:
- Kconfig
- Makefile
- inv_ami306_core.c
- inv_ami306_ring.c
- inv_ami306_trigger.c
- inv_ami306_iio.h
- inv_yas53x_core.c
- inv_yas53x_ring.c
- inv_yas53x_trigger.c
- inv_yas53x_iio.h

Integrating the Driver in the Linux Kernel
==========================================
Please add the files as follows:
- Add all above files to drivers/staging/iio/magnetometer/inv_compass
(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/magnetometer/Kconfig" with:
    >> source "drivers/staging/iio/magnetometer/inv_compass/Kconfig"

    modify "drivers/staging/iio/magnetometer/Makefile" with:
    >> obj-y += inv_compass/


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.

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

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:

AMI306
-------------------------------------------------
static struct mpu_platform_data compass_data = {
        .orientation = {   0,  0,  1,
                           0,  1,  0,
                           1,  0,  0 },
};

static struct i2c_board_info __initdata chip_board_info[] = {
        {
                I2C_BOARD_INFO("ami306", 0x0E),
                .platform_data = &compass_data,
        },
};

YAS53x(Use YAS532 as an example)
-------------------------------------------------
static struct mpu_platform_data compass_data = {
        .orientation = {   0,  -1, 0,
                           1,  0,  0,
                           0,  0,  1 },
};

static struct i2c_board_info __initdata compass_board_info[] = {
        {
                I2C_BOARD_INFO("yas532", 0x2E),
                .platform_data = &compass_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:

AMI306
--------
compass_matrix (read-only)
--show the orientation matrix obtained from the board file.

sampling_frequency(read and write)
--show and change the sampling rate of the sensor.

YAS53x
---------------------
YAS53x has all the attributes AMI306 has. It has one more additional attribute:

overunderflow(read-only)
--value 1 shows an overflow or underflow happens. Need to write into it to make
  it zero.

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

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

1. Write the desired output rate to sampling_frequency.
2. Write 1 to enable to turn on the event.
3. Read /dev/iio:device0 to get a string of gyro/accel/compass data.
4. Parse this string to obtain each compass element.

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
---------------------------------------------------------
To run test applications with AMI306 or YAS53x devices,
please use the following commands:

1. for ami306:
   mpu_iio -n ami306 -c 10 -l 3

2. for yas532:
   mpu_iio -n yas532 -c 10 -l 3

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