MagneticSensorSPI and STM32 #82
Description
As reported here:
https://community.simplefoc.com/t/sensor-as5047p-spi-reads-0-angle-with-stm32f103-aka-blue-pill/886/18
but also by other users, I think. It explains the difficulties some people (including myself) were having with magnetic sensors and STM32.
Here is my summary from that post:
Hey, I did a quick test setup:
[image]
- SimpleFOC 2.1.1 master branch (current normal version of the library)
- BluePill STM32F103C8
- AS5047P sensor
- PlatformIO, STM32 support v13.0
- Motor not connected, just the sensor
I can report the following:
It actually works out of the box, with no modifications to MagneticSensorSPI.cpp.
The resulting speed is too fast for my crappy logic analyser, the oscilloscope shows the clock line is at 9MHz:
[image]
That makes sense since we set the pre-scaler to 8, and 72MHz system clock / 8 = 9MHz SPI clock in this case.
Surprisingly, this is working fine even via the SPI hub and all the cables:
[image]
With my suggested modifications to MagneticSensorSPI, the picture changes to:
[image]
So now we don’t set the pre-scaler, but rather allow beginTransaction() to apply the clock_speed as specified in the settings object.
So we get 1MHz SPI clock, as specified in the settings.
To me this confirms the following:
the standard settings kind of work with STM32. But the bus speed does not get set, via the settings, resulting in a MCU-dependent default bus speed via the pre-scaler setting of 8, which is often much too high. I’m surprised my setup works at 9MHz, and I think if there were a BLDC driver and motor running chances are it wouldn’t work well any more.
the current code prevents the bus speed from being set correctly on STM32, so as a result, many people will have trouble with the current code under STM32 (as we see in this thread).