serial-protocols: document GPS, and list the missing protocols - #550
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The protocol list on this page named seven protocols. The receiver offers ten. GPS, MAVLink and DisplayPort were all absent, and the page had no GPS section at all even though the protocol has shipped since 4.0. Add a GPS Notes section covering the parts a user has to get right: - Wiring is one way. Only the GPS TX to receiver Serial RX line is needed, because SerialGPS never transmits. - The port is opened at 115200 baud 8N1 and there is no auto detection. Most modules ship at 9600 baud, so this is the likely first failure. - GGA, VTG and RMC are the only sentences read, and the talker ID is not checked, so any prefix works. GGA sends the position frame, VTG is folded into the next GGA frame, and RMC sends the time frame. - Each GGA produces a telemetry frame, so the GPS output rate has a direct cost in telemetry bandwidth. Note which protocols are restricted to one interface. Tramp and SmartAudio are Serial2 only, and MAVLink is Serial 1 only. The Lua page claimed Protocol 2 had the same options as Protocol, which is not true for MAVLink. Add GPS to the Lua Protocol list.
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The protocol list on this page names seven protocols. The receiver offers ten (
RXParameters.cpp).MAVLink,DisplayPortandGPSwere all absent, and there was no GPS section at all even though the protocol has shipped since 4.0.GPS Notes
A new section covering the parts a user has to get right, all taken from
SerialGPS.cppandrx_main.cpp:SerialGPS::sendQueuedData()has an empty body, the receiver never transmitsserialBaud = 115200for Serial 1 andSerial1.begin(115200, SERIAL_8N1, ...)for Serial2;serialConfigdefaults toSERIAL_8N1and is only changed for SBUS and HoTTGGA,VTGandRMCare readprocessSentence()sentence[3..5], so$GP,$GNand others all workGGAsends the position frame,VTGis folded into the nextGGAframe,RMCsends the time framesendTelemetryFrame()on GGA, the VTG call is commented out with "VTG usually comes before GGA, only generate one telemetry frame with both combined",sendGpsTimeTelemetryFrame()on RMCisValidChecksum()#if defined(PLATFORM_ESP32)guard aroundsetupSerial1()The baud rate is the one that matters in practice. It is hardcoded and there is no detection, while most GPS modules ship set to 9600 baud, so a stock module produces no telemetry at all. That has a warning.
Two other corrections
MAVLinkandDisplayPortas well asGPS. Added, with a note thatTrampandSmartAudioare Serial2 only andMAVLinkis Serial 1 only.Protocol 2"has the same options as the setting above". Serial2 has noMAVLinkoption, so that is now stated.GPSis also added to the LuaProtocollist, which omitted it.Not included
I did not document EdgeTX sensor names or a required EdgeTX version for the GPS time frame. Those cannot be verified from the firmware, so they are better added by someone who can confirm them on a handset.
NMEAis added to.wordlist.txtfor the spellcheck.wordlist.dicis left alone since it is generated.