[BUG] LowPassFilter::operator() returns nan

[manuelbaum]

Describe the bug
LowPassFilter::operator() returns nan when called with zero dt and zero Tf.

I have a multi-threaded setup running where I asynchronously call FOCMotor::shaftAngle() from different threads. Occasionally my setup breaks down because the LPF returns nan. That happens because the LPF is initialized with zero Tf in the FOCMotor class and occasionally dt is also zero which then breaks the formula in LowPassFilter::operator():

float alpha = Tf/(Tf + dt);

I'm actually surprised that nobody else had this problem yet, so I'm wondering if I am doing sth wrong.

hardware setup

• Motor: GB4106
• Driver: DRV8313
• MCU: ESP32
• Sensor: AS5048
• No current sensing

IDE

• Platformio

Suggested Solution
Catch the zero case by turning

if (dt < 0.0f ) dt = 1e-3f;

into

if (dt <= 0.0f ) dt = 1e-3f;

But I think that 1e-3f is actually a little too large and would suggest to go with 1e-4f or 1e-5f