[STM32F411RE Nucleo Board] How to set SPI interface to a baudrate of 100kHz or less?

[joern20]

Hi All,
My setup:
ST Nucleo F411RE
Micropython v1.19.1

I want to set the baudrate of the SPI to 100khz or less because the peripheral I want to talk to is only specified for up to 100khz. I learned already here that there are three options to achieve this:

Option 1: Using pyb.SPI setting the prescaler
SPI.init(mode, baudrate=328125, *, prescaler=- 1, polarity=1, phase=0, bits=8, firstbit=SPI.MSB, ti=False, crc=None)
The highest prescaler which has an effect is 256, 512 doesn't have an effect. The lowest baudrate I was able to set is 187khz using 256.

Option 2: Using pyb.SPI or machine.SPI setting the baudrate
Here the same like for option 1 the lowest baudrate is 187kHz

Option 3: Adjusting the CPU clock using pyb.freq() or machine.freq()
This option causes the board to stop functioning after placing the command in the boot file and restart the board e.g. pyb.freq(64000000) to set the clock to 64Mhz (Default CPU clock is 96Mhz). I can't access it anyore via USB independent if pyb or machine class was used. How to apply and what to respect using the function is described herehttps://docs.micropython.org/en/latest/library/pyb.html#module-pyb section Power related functions pyb.freq().

My question is how can I adapt the CPU clock to be able to adjust the SPI baudrate to 100khz or less by reducing the CPU clock?
So far I think reducing the CPU clock is the only possibility.
Thanks.

[joern20]

I was able to solve the problem by using Soft SPI implemented in the machine module.
Soft SPI is described here It is not very acurate, but sufficient.