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cvra / robot-software

CVRA monorepo - All software running on our bots lives here
MIT License
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Implement software SPI workaround for pressure sensor #300

Closed antoinealb closed 3 years ago

antoinealb commented 3 years ago

@nuft identified that for some reason there is a conflict between the SPI driver and the servo motor PWN; turning on the servo means the SPI hardware starts misbehaving immediately. This is likely not a PCB issue, as the problem starts as soon as the peripheral is enabled, even if no signal is coming out of the chip.

Two workarounds were possible: either using a software PWM or a software SPI. Servomotors require rather precise PWM signals, as the use pulse width to determine which position they should have. Therefore, I am more incline toward using a software SPI, which despite being slow, requires no accurate timings.

This commit implements a basic software emulation of SPI, with just the modes required for communication with the pressure sensor. I could not test it on hardware, but I have written unit tests for it. Support for calibrating the data rate is present, but I don't have the required instruments to do it available.

Note that since this SPI driver is based on busy waiting, the calling thread will be using CPU, so some thread priorities might need to be adjusted.

msplr commented 3 years ago

Looks good to me. I’ll test it on hardware asap.