Overhaul of interrupt-based sensors to eliminate bad readings due to interrupts modifying variables in the middle of get functions.
All sensor classes are now required to use the base class state variables, and do their angle reading once per frame in the update() function rather than using the virtual get functions to return real-time updated readings. I have chosen to make an exception for getVelocity() and allow it to access volatile variables as well, although it may be better to merge it into update() instead. Interrupts should be disabled/enabled as necessary in the update() and getVelocity() functions, and preferably nowhere else. The Arduino library provides no mechanism to restore the previous state of interrupts, so use of the unconditional enable should be kept to as few locations as possible so we can be reasonably sure that it won't be called at a time when interrupts should remain disabled.
Additional changes to specific sensors:
HallSensor: Removed the max_velocity variable because it was a quick fix for bad velocity readings that were coming from this interrupt problem, which should no longer occur. Also changed the condition for "velocity too old" from (_micros() - pulse_timestamp) > pulse_diff to (_micros() - pulse_timestamp) > pulse_diff*2, because any deceleration would cause inappropriate reporting of zero velocity.
MagneticSensorPWM: Unrelated to the interrupt problem, timestamp is now saved from the rising edge of the PWM pulse because that's when the angle was sampled, and communicating it takes a significant and variable amount of time. This gives more accurate velocity calculations, and will allow extrapolating accurate angles using the new SmoothingSensor class.
Sensor: Added friend class declaration for SmoothingSensor. Alternatively we could make prev_angle_ts public, and I could use getMechanicalAngle() and getFullRotations() to access the other state variables.
dekutree64
commented
1 year ago
Overhaul of interrupt-based sensors to eliminate bad readings due to interrupts modifying variables in the middle of get functions.
All sensor classes are now required to use the base class state variables, and do their angle reading once per frame in the update() function rather than using the virtual get functions to return real-time updated readings. I have chosen to make an exception for getVelocity() and allow it to access volatile variables as well, although it may be better to merge it into update() instead. Interrupts should be disabled/enabled as necessary in the update() and getVelocity() functions, and preferably nowhere else. The Arduino library provides no mechanism to restore the previous state of interrupts, so use of the unconditional enable should be kept to as few locations as possible so we can be reasonably sure that it won't be called at a time when interrupts should remain disabled.
Additional changes to specific sensors:
HallSensor: Removed the max_velocity variable because it was a quick fix for bad velocity readings that were coming from this interrupt problem, which should no longer occur. Also changed the condition for "velocity too old" from (_micros() - pulse_timestamp) > pulse_diff to (_micros() - pulse_timestamp) > pulse_diff*2, because any deceleration would cause inappropriate reporting of zero velocity.
MagneticSensorPWM: Unrelated to the interrupt problem, timestamp is now saved from the rising edge of the PWM pulse because that's when the angle was sampled, and communicating it takes a significant and variable amount of time. This gives more accurate velocity calculations, and will allow extrapolating accurate angles using the new SmoothingSensor class.
Sensor: Added friend class declaration for SmoothingSensor. Alternatively we could make prev_angle_ts public, and I could use getMechanicalAngle() and getFullRotations() to access the other state variables.