Adding RTK functionalities to Solo

[klopezal]

This pull request aims at adding data injection functionalities to 3DR Solo in order to use with u-blox M8P (RTK) chip. Drotek has specifically made an upgrade for it. It brings support for the GPS_INJECT_DATA and GPS_RTCM_DATA MAVlink messages. Ground control station is connected to M8P base and sends differential data packets over Solo Link and does not need any additional datalink. Flight controller then parses and potentially reassembles data structures to send them to the M8P over the existing serial connection. M8P can provide centimeter-level accuracy positioning.

[WickedShell]

This is mostly a duplication of effort of the work here: ArduPilot/ardupilot#5498

Because you haven't swapped to the PVT message you don't have a good indication that you are actually using RTK or if you have a SBAS system. For a normal solo user this will instead be reporting DGPS for all SBAS usage, which will be misleading to a lot of users, especially if you begin to publish documentation that says having DGPS is equivalent to having a RTK fix.

[proficnc]

As Michael has mentioned, this is a duplicate of the work going into Ardupilot master, which is already out at hardware beta testers for the Here+ RTK kit (Base and Rover)
This Should be in the 3.5 Beta release in the next few weeks. so the Drotek module will be able to make use of this.

[klopezal]

I agree with you about the PVT message, but this is supposed to be a first step forward to provide RTK functionalities to Solo. The "dgps" flag is incomplete as you say, because indeed it does not tell you whether you are using a fix, float or SBAS solution (we are only reading the diffCorr bit in NAV-STATUS or NAV-SOL ubx message), but at least you know you are receiving differential corrections. The idea there was to provide a quick support for M8P, and then move to the PVT message once it is fully supported. Ardupilot master breaks gimbal functionalities on Solo, so this is the main reason for this PR.

[proficnc]

No, gimbal works fine! We would love any help on the effort to get this on master. No point replicating work :). There has been a huge amount of work to get master running on Solo.

[klopezal]

I am unable to get Solo gimbal working either with v2 or v3 targets on Ardupilot master, is there something I am doing wrong?

Again I understand your point, but the point there was to provide immediate support for our Drotek RTK Solo board on a stable and tested version.

[proficnc]

Best jump over and raise issues on Ardupilot, so we can cooperate and get this on master faster.

We aim to get it flying well very soon.

The good thing with the M8P, it is a great GPS even without RTK, so it doesn't hurt for people to get them in preparation

[klopezal]

One does not preclude the other, after all :)

[proficnc]

Exactly :)