The clock of my STM32F303CC (links to datasheet; for reference manual see here) sporadically dies away, resulting in highly decreased code execution speed (see picture below). I already replaced the oscillator and experimented with different capacitor values. I also tested this on different boards, all exhibiting the same error.
The firmware of the STM32 always runs the same lines of code, so transitions in firmware code can't be the reason.
The components used are:
- Oscillator: 7A-8.000MAAE-T
- Capacitors: 2x 22pF, 6V3, 0603, C0G
Any idea why this happens?
Edit: Replaced layout image as I forgot to render polygons.
Edit: The decoupling capacitors are on the direct opposite of the board, just beneath the STM, and are connected through vias with both top's GND and 3V3 pins (former through PCB wire, latter through the copper plane).