ChibiOS Free Embedded RTOS

I had the same problem. If I understand correctly, the question is simple
BYPASS->TRUE you have to provide a clock source, a stable waveform provided by an external oscillator or chip
BYPASS->FALSE you have two PINs representing the input and the output of the feedback loop of a Colpitts oscillator ...

Giovanni,
this is not correct:
If you have an oscillator then you need the bypass.


Bit 18 HSEBYP: HSE crystal oscillator bypass
Set and cleared by software to bypass the oscillator with an external clock. The external clock
must be enabled with the HSEON bit set, to be used by the device. The ...