This library communicates with InvenSense MPU-9250 and MPU-9255 Inertial Measurement Units (IMUs).
The InvenSense MPU-9250 is a System in Package (SiP) that combines two chips: the MPU-6500 three-axis gyroscope and three-axis accelerometer; and the AK8963 three-axis magnetometer. The MPU-9250 supports I2C, up to 400 kHz, and SPI communication, up to 1 MHz for register setup and 20 MHz for data reading. The following selectable full scale sensor ranges are available:
| Gyroscope Full Scale Range | Accelerometer Full Scale Range | Magnetometer Full Scale Range |
|---|---|---|
| +/- 250 deg/s | +/- 2g | +/- 4800 uT |
| +/- 500 deg/s | +/- 4g | |
| +/- 1000 deg/s | +/- 8g | |
| +/- 2000 deg/s | +/- 16g |
The MPU-9250 samples the gyros, accelerometers, and magnetometers with 16 bit analog to digital converters. It also features programmable digital filters, a precision clock, an embedded temperature sensor, and programmable interrupts.
CMake is used to build this library, which is exported as a library target called mpu9250. The header is added as:
#include "mpu9250/mpu9250.h"
The library can be also be compiled stand-alone using the CMake idiom of creating a build directory and then, from within that directory issuing:
cmake .. -DMCU=MK66FX1M0
make
This will build the library and example executables called i2c_example and spi_example. The example executable source files are located at examples/i2c.cc and examples/spi.cc. Notice that the cmake command includes a define specifying the microcontroller the code is being compiled for. This is required to correctly configure the code, CPU frequency, and compile/linker options. The available MCUs are:
- MK20DX128
- MK20DX256
- MK64FX512
- MK66FX1M0
- MKL26Z64
- IMXRT1062_T40
- IMXRT1062_T41
These are known to work with the same packages used in Teensy products. Also switching packages is known to work well, as long as it's only a package change.
The i2c_example and spi_example targets create executables for communicating with the sensor using I2C or SPI communication, respectively. Each target also has a _hex for creating the hex file to upload to the microcontroller.
This library is within the namespace bfs.
This driver conforms to the IMU interface; please refer to those documents for information on the ImuConfig and ImuData structs.
bool Init(const ImuConfig &ref) Initializes communication with the IMU, configures it according to the ImuConfig struct, and estimates gyro biases to be removed during Read. Note that the bus is not started within init and should be initialized elsewhere. Returns true on successfully initializing and configuring the IMU.
/* Mpu9250 object */
bfs::Mpu9250 imu;
/* Config */
bfs::ImuConfig config = {
.bus = &SPI,
.dev = 24,
.frame_rate = bfs::RATE_50HZ,
.accel_bias_mps2 = Eigen::Vector3f::Zero(),
.mag_bias_ut = Eigen::Vector3f::Zero(),
.accel_scale = Eigen::Matrix3f::Identity(),
.mag_scale = Eigen::Matrix3f::Identity(),
.rotation = Eigen::Matrix3f::Identity()
};
/* Init the bus */
SPI.begin();
/* Initialize and configure IMU */
if (!imu.Init(config)) {
Serial.println("Error initializing communication with IMU");
while(1) {}
}bool Read(ImuData * const ptr) Reads data from the IMU and passes the data into the ImuData struct. Returns true on successfully reading new data.
/* IMU data */
bfs::ImuData data;
/* Check if data read */
if (imu.Read(&data)) {
}