I agree, I just like to avoid those family specific ifdefs whenever possible.  If there is no other way to detect this, please add a comment as to why STM32F411xE gets special treatment here. What about STM32F410? Those can also run at 100 MHz.    Would testing for `RCC_PLLSAI_SUPPORT` be an option or are there MCUs where `RCC_PLLI2S` can be used for USB?