STM32F070 APB1 clock can't be configured with HSI clock

[XR.1]

Hi,

APB1 clock can't be enabled if HSI clock is chosen. It says that the driven clock must be 10M<=x<48M, so, without using the PLL it's impossible to get the 10MHz.

Things get worse when I try to feed the PLL from the HSI: it says that the PLL should have HSE as an input!

If I go on despite the recommendation, then I get this message:

How can I enable the APB1 clock without using an externa crystal?

What should I do if I want to choose both: not to use an external crystal and still using the USB peripheral?

For now I can disable the USB port because I'm not in a rush with it, but this isn't a solution.

May I overlooking something?

BTW, this is a custom board.

Thank you in advanced!

[mƎALLEm · Accepted solution]

Hello,

In that device, USB needs an external crystal to work without issues. So if you are not using USB, disable it. If you need to use USB in the future you need to use HSE+ an external crystal.

[XR.1]

I thought I read somewhere that in this part the USB module was crystal less, and clearly I was embarrasingly wrong. I disabled USB and things got better. 

Thank you!