Porting to FEZ Cerb40 board

I'm not 100% sure I'm afraid - you're on the right track with targetlibs/stm32f4/lib/system_stm32f4xx.­c - try setting HSE_VALUE too in stm32f4xx.h (this could be done with a DEFINES+= in the Makefile).

I guess if you looked at the serial port waveform with an Oscilloscope you might get an idea of how fast/slow it was running...