IMU configuration

Now that we've confirmed communication with the IMU, we can proceed to the next step. The IMU starts with all sensors disabled, so in order to take any measurements, we need to configure the chip.

There are other useful settings that we'll want to change, but for now, we'll focus on the most critical ones in registers CTRL1 and CTRL7.

We will use a configuration builder similar to those provided by esp-hal peripherals. Let's start by defining our struct:

#![allow(unused)]
fn main() {
#[derive(Debug)]
pub struct Config {
    ctrl1: u8,
    ctrl7: u8,
}
}

We'll implement the Default trait, so that we can create an instance of our Config. We're using the default values from the datasheet.

#![allow(unused)]
fn main() {
impl Default for Config {
    fn default() -> Self {
        Self {
            ctrl1: 0b0010_0000,
            ctrl7: 0b0000_0000,
        }
    }
}
}

Now that we've got the default configuration, we need to provide a way to change the settings. Let's look at a few functions as an example:

#![allow(unused)]
fn main() {
impl Config {
    // CTRL1
    pub fn with_3_wire_spi(mut self) -> Self {
        self.ctrl1 |= 1 << 7;
        self
    }

    pub fn with_address_auto_increment(mut self) -> Self {
        self.ctrl1 |= 1 << 6;
        self
    }

    pub fn with_little_endian_data(mut self) -> Self {
        // Note: the bit is set by default, so we provide an API to clear it.
        self.ctrl1 &= !(1 << 5);
        self
    }

    // ...
}
}

Implement the remaining methods for CTRL1 and CTRL7 registers.

IMU initialization

In order to make use of the configuration, we need to be able to write the data to the chip. Let's add an initialize() method to our IMU instance to do just that:

#![allow(unused)]
fn main() {
pub fn initialize(&mut self, config: Config) -> Result<(), I2C::Error> {
    self.i2c.write(self.address, &[registers::CTRL1, config.ctrl1])?;
    self.i2c.write(self.address, &[registers::CTRL7, config.ctrl7])?;
    Ok(())
}
}

Bringing it all together

Finally, in the main.rs, we can create our configuration and initialize the IMU:

#![allow(unused)]
fn main() {
let imu_config = qmi8658a::Config::default()
    .with_address_auto_increment()
    .with_gyro_enabled()
    .with_accelerometer_enabled();
}

And then pass the imu_config to the initialize() function:

#![allow(unused)]
fn main() {
imu.initialize(imu_config).expect("failed to initialize IMU");
}