I'm currently troubleshooting a STM32H750 QSPI implementation, and wanted to check that the prescaler was running correctly. So, on page 892 of RM0433 it shows a feature in the QUADSPI CCR called FRCM (free running clock mode). The catch is none of the STM32Cube or CMSIS code has a definition for this bit. In its place, I manually ORed this bit into the QUADSPI CCR, which produced an interesting result:
First, the QSPI clock went from high-Z to high (about 3.2V) on my oscilloscope. It did not toggle after this. About 15-20 seconds after the QSPI clock went high, the debugger I was using (J-Link) reported that it had lost connection with the target, and I had to restart the CPU.
Is the FRCM bit an officially supported feature, and if so, are there any specific implementation issues with respect to using it? Finally, if that's supposed to work - what other issues could I be facing when I don't see a QSPI clock coming out after setting this bit in the CCR?
