ChibiOS Free Embedded RTOS

This is very strange, could you try to clear just the SPE bit instead of all SPI registers?

It was really confusing because the coupling between spi, stop modes, and flash was really strange. I ended up writing a stand alone program to test just this path. In the end, I had to explicitly handle restarting power modes and flash after stop modes. Once that was done, your changed spi driver works fine. What the connection between the two is far from clear, but my best guess is that by not clearing the spi device, the actual stop mode wasn't being entered (a silent fail on the part of the stm32u375). I base this guess on actually measuring the current when the device was supposed to enter stop1.

Thanks for your help in chasing this! I do think the changes to spiStop are needed.

It is possible that the logic for entering stop mode checks for the various peripherals state, the problem is that such failed check is not logged anywhere as error status apparently.

Giovanni