My application is running on the STM32F746 Discovery kit (STM32F746BG chip). mIf I initialize the system clock to its maximum of 216MHz early in the application, the SDIO (ST calls it SDMMC in the F7 series - why they do I just don't know!)) peripheral stalls and doesn't initialize in the PowerOn() routine.
However, if I run the system clock at a lower speed, e.g. 96MHz and then increase it to the maxmium 216MHz after the SDIO interface has initialized, it works and the rest of the application proceeds as normal.
The SD card bus speed is not effected by this change in SysClock speed since the SD card bus clock is derived from a dedicated 48MHz PLL. I've also made sure the initial SD card bus speed is at the recommended 400KHz.
I have read the datasheet, the reference manual and the errata sheet for that chip and couldn't see any reason why this is so.
Can anyone shed any light on this?