SystemCoreClock and USB clock settings dependency (STM32 series) #1408
Description
In case you want to use the USB device (or host) features the core clockspeed has to have certain values otherwise you can not get the correct USB clock of 48 MHz. On the F103 for example you can run at 72 MHz core speed with 8MHz external clocks (PLL: 8x9 = 72, USB: 72/1.5=48), but you can only get a maximum of 48 MHz core speed using the 8 MHz HSI (PLL: (8/2)x12 = 48, USB: 48/1=48).
It would be nice to include #define settings for USB in system_stm32fxxx.c. It would be even better when these selections can be set without importing and modifying the mbed lib source.
See also discussion on issue #1096 regarding timeout for clock auto-select.