On Dienstag, 3. März 2020 18:41:43 CET Attila Kinali wrote: > On Tue, 03 Mar 2020 14:42:49 +0100 > > Matthias Welwarsky <[email protected]> wrote: > > In the meantime, I'm thinking of another modification to make: getting rid > > of the HC390 ripple counter. I think I might be able to use the STM32 as > > a frequency divider. I just have to figure out how to program the timers. > > What might work is the following: > > > > - Feed the 10MHz clock into the external trigger input for the timer, > > configure the timer to count the trigger pulses instead of the internal > > clock source. > > Better idea: feed the 10MHz input directly into the clock input > RCC_OSC_IN and let the STM32 derive its internal clock from that. > Doing that, the clock of your timer unit will be phase locked to > the 10MHz signal. Then you can use the timer for both capturing > the incomming PPS and for generating the 250kHz. The capturing > will solve the issue with aliasing. The timer output should have > a jitter in the low ps range. There is a bit more going on than > you would want in the STM32 for a low noise signal, but most > likely not so much as to degrade the output enough to matter. > If you are worried about that, you can still add a 7474, with > D connected to the STM32 timer output and the CLK to the 10MHz > to clean the jitter. But as I said, that's probably not necessary > in this case.
I have an STM32F042 without FPU and I'm doing a lot of double precision math. I'm not sure I can spare the 4/5th of the cycles. > > If you want to create a stabilized output PPS from the STM32, > you will need to do some software trickery to align the PPS, > as you cannot hope to shift the phase of the Rb in a reasonable > time to match up. That's not very high on my laundry list. > > Attila Kinali _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
