GPS without SIM works for me. I just removed the SIM and booted Mobian from eMMC with no SD present. It's not been updated in a while, but it's the one that has my agps script present and commands in the bash history so it was easier to try. WiFi was connected so I could still download the agps data.
sudo systemctl disable ModemManager.service
sudo systemctl stop ModemManager.service
./load_agps_data
picocom /dev/ttyUSB1
Unless I've forgotten about some config I've done to picocom at some point in the past, it should now show blocks of NMEA data updating every second - something like this block (sats being tracked but no fix yet):
$GPGSV,2,1,06,18,53,146,22,31,32,198,25,02,,,,04,10,291,,1*54
$GPGSV,2,2,06,05,15,045,,09,08,327,,1*65
$GPVTG,,T,,M,,N,,K,N*2C
$GPGSA,A,1,,,,,,,,,,,,,,,,*32
$GPGGA,,,,,,0,,,,,,,,*66
$GPRMC,,V,,,,,,,,,,N*53
After a few minutes indoors without a fix I took it outside, and got a fix within a couple of minutes I guess. I've seen much quicker fixes, but I've seen worse too so can't tell if I just got unlucky, or some change is making it harder to get a fix. When you get a fix you'll see time, lat and lon filled in in the GPGSA and GPRMC lines, among other changes.
I should point out that means the hardware works, not that ModemManager can use it yet.
sudo systemctl disable ModemManager.service
sudo systemctl stop ModemManager.service
./load_agps_data
picocom /dev/ttyUSB1
Unless I've forgotten about some config I've done to picocom at some point in the past, it should now show blocks of NMEA data updating every second - something like this block (sats being tracked but no fix yet):
$GPGSV,2,1,06,18,53,146,22,31,32,198,25,02,,,,04,10,291,,1*54
$GPGSV,2,2,06,05,15,045,,09,08,327,,1*65
$GPVTG,,T,,M,,N,,K,N*2C
$GPGSA,A,1,,,,,,,,,,,,,,,,*32
$GPGGA,,,,,,0,,,,,,,,*66
$GPRMC,,V,,,,,,,,,,N*53
After a few minutes indoors without a fix I took it outside, and got a fix within a couple of minutes I guess. I've seen much quicker fixes, but I've seen worse too so can't tell if I just got unlucky, or some change is making it harder to get a fix. When you get a fix you'll see time, lat and lon filled in in the GPGSA and GPRMC lines, among other changes.
I should point out that means the hardware works, not that ModemManager can use it yet.