Did anyone attach an USB-TTL module to STM32, PA9 TX —-> Rx of USB-TTL and PA10 RX —-> Tx of USB-TTL to see if there are things/text coming out from the controller ?
Indeed a pity that this GPSDO does not have a serial interface with NMEA output....
It means no opportunity to see a lot of information that makes the use of a GPSDO more reliable, and makes it better to understand what is going on. Such as info on number of satellites received, their SNR., Azimuth and Elevation Graph, HDOP and VDOP) parameters etc.
See for an example of a NMEA monitor:
VisualGPSView It also precludes the use of Lady Heather.
Normally I would expect NMEA output on the TX terminal of the GPSDO module, but I do not know this ATGM 336H module.
Probably the STM32 also uses this port for communication. But as NMEA is a read-only data stream, it might be possible to read out the TX port in parallel. When the STM32 communicates only at startup with the GPSDO module (to set the module up), there might still be a clean NMEA stream at the TX output.
And, maybe, BH3SAP made the NMEA data available at an output pin of the STM32.
This, as well as the output of the GPS module, is easy to check with an oscilloscope.
Regards, Gertjan.