I’m using the MC60 in a GPS-based car tracking project. The idea is to query a RMC sentence, process the result and send a packet to a server, all of this once every second.
I’m able to successfully turn on the GNSS engine and query a RMC NMEA sentence with the AT+QGNSSRD command.
However after getting a first fix the module always returns the exact same sentence for an undefined length of time. I mean if I use the AT+QGNSSRD several times, the MC60 returns the exact same sentence each time. With the same time, date, position, speed, etc. It can last anywhere from 10 seconds (so 10 queries) to 30 minutes, the longest I’ve tried.
At first I thought they was maybe a kind of mechanism that updated the fix only if some movements was detected but that’s not the case as the problem still occurs when testing in a moving car.
I didn’t change any internal setting on my module.
Is it supposed to be the normal behavior ? If not, is there a way to fix this ?
After further testing, it turns out that two AT+QGNSSRD command calls will return the same string only when I send the processed data via UDP in the meantime.
If I comment out the part of my code that is responsible of sending the data, the command result is updated each time.
According to the signals I see with my oscilloscope my code works correctly so I don’t really understand what happens here.
Here are some recordings in case it might be useful :
On the following picture we can see the command in blue and its answer in purple. The data in the answer from the GPS doesn’t change each time as it should. This is what I get when I send the data via UDP between calls to AT+QGNSSRD :
Here we can see that the data is sent (“SEND OK”) but the RMC sentence is always the same.
According to this picture the transmission seems to overlap. This is due to recording software. I can provide a picture showing the actual signals to prove that they do not overlap (I didn’t post it in this post since new users can only send one picture per post).
EDIT : Here is the picture showing that the signals do not overlap :
I tried to disable pdp context with AT+ QIDEACT after sending a packet. After that the GPS is like reset and search for a fix again. It looks like GPS and GPRS cannot coexist on my device. When the module is in a “data sending state” (network led blinking every 600ms), the GPS doesn’t work anymore. Is this normal ?
