In an SIM808 chip or similar you can get the GPS information with this AT command:
AT+CGNSINF
+CGNSINF:1,1,20150327014838.000,31.221783,121.354528,114.600,0.28,0.0,1,,1.9,22,1.0,,8,4,,,42,,
the UTC time is in the third data field as: yyyyMMddhhmmss.sss
However in the manual the function of AT+CGNSSEQ
is described as: Define the last NMEA sentence that parsed.
My question is in general:
- how accurate is this time when I receive it from the serial interface of the chip?
Sub questions:
- Should I assume that the time between the AT command answer and the last NMEA message that was received by the GPS unit is variable?
- Can I compensate for delays in the systems and how?
Delays I expect:
Difference between NMEA sentence coming in and AT command?
Time to process NMEA sentence
Time to read AT command and prepare response
Serial communication time