Your first heading

The goal from unboxing to a working heading in robot code is under five minutes with no prior knowledge. If it takes longer, that is a documentation bug — please report it.

Wire it

ROTEM takes 6–28 V and CAN on a single Micro-Fit connector, and the two connectors are wired in parallel so the device daisy-chains into your bus. Close both termination jumpers only if the module sits at a physical end of the bus; opening either one disables the whole termination network.

Read it

import com.sapphify.frc.hardware.CoreRotem;

public class Drivetrain {
  private final CoreRotem imu = new CoreRotem(0, transport);

  public double getHeadingDegrees() {
    var yaw = imu.getYaw();
    if (!yaw.isValid()) {
      // The device is not answering. Keep the last good pose rather than
      // feeding a garbage heading into the estimator.
      return lastKnownHeading;
    }
    lastKnownHeading = yaw.value();
    return lastKnownHeading;
  }
}

Device number 0 is the factory default. It is stored in flash and survives power cycles, and you can change it over USB with no bus and no deployed robot code.

Then read whether to trust it

This is the part other IMUs do not offer, and the reason to bother:

var sigma = imu.getYawUncertainty();   // the filter's own 1σ, in degrees
var drift = imu.getAccumulatedDrift(); // estimated error since the last zero

for (String alert : imu.getActiveAlerts()) {
  DriverStation.reportWarning(alert, false);
}

An alert reads like ROTEM AHRS 0: high vibration. Check swerve module bearings and belt tension — it names the likely mechanical cause, because the person reading it in the pit is usually not the person who wrote the code.

Zero it

imu.zeroYaw();

Call this when the robot is stationary and squared to the field. Heading is not absolute unless an absolute reference has been accepted, and the uncertainty signal tells you how much that matters.