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ST32F407 "HSI as USB CDC" or "Separating SYCLK from USBCLK"

Question asked by h..marc on May 29, 2013
Latest reply on May 30, 2013 by h..marc
we want to implement a pulse generator with Timer1, clocked by SYCLK. For marketing reasons we'd prefer a granularity of 10ns, therefor we'd set SYSCLOCK to 100MHz.
At the same time we'll need a USB CDC for our user interface (FS-interface, device only).
Crosschecking the HSI-spec (factory accuracy -8..4,5%) and the USB2 spec, should rule out using HSI as USB clock.
On the other hand, we're pretty sure that the DFU-bootloader runs from HSI.

So - does anybody have experiences with using HSI as USB clock?
Or - even better - any suggestions for both basing 100MHz-SYSCLOCK and 48MHz-USBCLOCK on a crystal?

Looking forward your ideas,