Trigger ADC by timer

[Lee3]

I'm having some difficulty getting this to work. This post is a very good description of the my confusion: https://community.st.com/s/question/0D50X00009XkghxSAB/triggering-adc-sampling-by-timer-events

However the conclusion is not helpful. TRGO update event triggering seems to work, but I'm interested in the CH* triggers. For example, I'd like to trigger the injected measurements off TIM8_CH4 event but I can't understand the documentation on what a CH4 event is. Is it a compare match? Is it an input capture? Either way I can't seem to get the ADC to trigger off it.

[S.Ma]

I use the timer output compare pin (channel) which I connect with jumper wire to the ADC trigger pin.

This way, it is possible to monitor with a scope what is going on. The timer create the ADC sampling frequency and the DMA will cyclically fill a rolling RAM array with the converted values when using a normal channel. Probably once this is working, it can be "optimized" by using internal signals.

[Lee3]

This was very helpful and the debugging method I took. First I used an actual output from TIM8_CH4 and connected to EXTI line 15 for injected measurement triggers. I was then able to work back to a working non wired option.

[waclawek.jan]

> I can't understand the documentation on what a CH4 event is. Is it a compare match? Is it an input capture?

Probably transition on the TIM8_CH4 output, enabled by both TIM8_CCER.CC4E and in case of TIM8 also TIM8_BDTR.MOE; but not necessarily brought out to pin through GPIO AF.

Yes, the documentation is, ehm, substandard in this regard.

JW

[Lee3]

This was exactly correct. In my case I think it was the CCxE I was missing. So the trigger signal is OCx, which is the signal just prior to actual output. The GPIO can be disabled.