Heltec v3 GPS support

[oltaco]

GPS support using EnvironmentSensorManager.

Tested with Ublox Neo-6M. Connect RX on GPS module to pin 45 and TX to pin 46.

Note that while you can enable and disable the GPS there is no way to actually power down the GPS module without using a mosfet and adjusting PIN_GPS_EN.

Closes: #328

[ripplebiz]

Could you do a timing test for me? I'm curious, for setups that DON'T have GPS wired up, how long does each EnvironmentSensorManager::loop() invocation take? Is probably fine, but just want to make sure there isn't any latency being added, eg to repeaters, with having that processing in every loop()

[oltaco]

Good call, will investigate and get back to you.

[oltaco]

So with ENV_INCLUDE_GPS=1 and GPS unwired EnvironmentSensorManager::loop() is taking 8-10 micros, with the occasional single loop spike to ~15-17us. The attached log has 20 seconds worth of measurement for this setup.

I also checked with GPS wired just to see what the hit would be. In that setup each second when a new NMEA message comes in every second or third loop takes ~215-240us, probably every time a new character is coming in over serial I guess?

envsenseman loop gps unwired.txt

[fdlamotte]

Thanks for the patch, my heltec with gps now gives me position with the dev branch (gps wired on 33/34/47, it also has an RST pin but its wiring doesn't seem necessary)

Maybe a configurable baudrate would be interesting (a GPS_BAUDRATE symbol), by chance my GPS was at 9600 (well that's the one with which MicroNMEALocationProvider was written, so the defaults might be my fault ...)