Hi All -
I'm trying to utilize an external uC to save the internal state of the GPS. To this effect, I'm utilizing the following messages at startup:
- UBX-MGA-INI-TIME_GNSS (restored to GPS time)
- Series of UBX-MGA-DBD commands saved from previous shutdown of GPS
- UBX-MGA-INI-POS_LLH - Saved position from previous shutdown of GPS
Should this behave similarly to a hot start for short periods of time if implemented correctly?
I'm getting much faster hot start times (less than a second) than I am with the saving and restoration of the state of the module which is not expected, but I also do not see any documentation on what the expected time for these circumstances are. One thing that surprised me is that the PPS coming out of the GPS does not align with the pushed GPS time right away, but still waits until the actual GPS lock although other messages coming out of the GPS indicate to me that it did indeed take in the time.
I'm syncing the clock to and from the GPS module with the uC utilizing the UBX-TIM-TP and UBX-MGA-INI-TIME_GNSS both configured to save GPS time and utilize a rising edge on their respective electrical signals. With an oscilloscope, I can see that the edges between the two (GPS generated edge vs uC generated edge) are within 1 RTC clock tick on the 32.768kHz clock - within approximately 31uS. (I'm also calibrating the RTC in our uC from the PPS signal to avoid drifting.)
(If it matters, we're using the EVA-M8M.)