I see the same happening on STM32H745I-Disco. Setting DDR mode in ConfigSpeedBusOperation will first try and set HighSpeed, which sets the ClockDiv from 8 to 2. In MMC_HighSpeed(..): sdmmc_clk = HAL_RCCEx_GetPeriphCLKFreq(RCC_PERIPHCLK_SDMMC); // = 2...