Using the new secondary COM port

[Evan Schellenberg]

Support for a secondary COM port was added to the autopilot recently. This is a port that always existed on G2 hardware but was not enabled in the software until now.

You will see the terms COM2 and RADB used in this post and within Horizon/VRS settings, they are being used interchangeably.

You will need to upgrade your firmware to a version that supports it, as well as add a connector to the lines used for it on the P1 connector. Versions of firmware/Horizon 3.7.1346.0 and newer will have all of the secondary COM port changes.

This port is the plug labelled "COM2" on the uLRC (microLRC) enclosure. There is no plug in the default wiring harness on board level autopilots for this port though.

To use both autopilot COM ports for redundant links you would need use two COM ports on the GCS computer, and you would need two modem pairs, or a modem that can do two serial channels.

VRS Setup
You can enable the secondary port in the VRS Editor "Comms" tab.

Once enabled with the "Enable on non-MP3X" checkbox the autopilot will only use one COM port at a time by default. The last active port is what will be used, the other will be ignored until the active link goes down (if you are using them for a redundant link, you want this). If you want to be able to do operations on both ports at the same time then turn on the "Process all links" option in the Comms tab.

This will then make the autopilot process packets on both com ports at the same time.

Horizon Setup
In Horizon settings, Comms tab, the 'Radio B COM# port" in the 3X settings area is the COM port on the PC that will be connected to the secondary port on the autopilot. **Leave the "Use mp3X" option off when using a single board**, the RADB COM port setting will be moved to a more appropriate section soon.

Set the COM port on your GCS computer that the secondary modem is connected to in the space that has "COM2" in it in this example image (it does not have to actually be COM2). Make sure the "Radio B COM port baud rate" matches the baud rate configured in the "COM2/RADB" section of your VRS.

The secondary COM port will function the same as the primary COM port that has always been used before. It is already at RS-232 serial level and will use the GCS protocol automatically.

Hardware Setup

The secondary COM port pins are on the P1 connector of the autopilot (the main COM port on the autopilot is on the P2 connector for reference).

P1, pin 2: TX line

P1, pin 4: RX line

P1, pin 1: Ground (only use if required and will not create a ground loop).

You can use these to connect to Horizon via a radio modem or the grey serial cable that comes with the autopilot starter kit.

More Info
For more details, see the release notes below to see what version has the specific changes to enable this port:

3.7.1335:

Linux XTENDER: added support for mpSetLinkBaud API so the mpDownloadDatalog API can reconfigure the datalog download baud rate on Linux (previously could only reconfigure baud rate on Windows XTENDER)

XTENDER: updated mpDownloadDatalog API to be able to reconfigure the baud rate of COM2/RADB via [reconfigureUart] field. See autopilotPort member of MPDATALOGDOWNLOADCONFIG struct.

Autopilot Firmware:
-new [reconfigureUart] field to reconfigure COM1 or COM2 baud rates.  Previously, only the primary COM1 baud rate could be configured by writing to the [gcsBaud] field.
-enabled COM2 on non-MP3X firmware.  See field [radioModemBOptions].

Horizon VRS Editor: added controls for [radioModemBOptions].  See Comms Tab and Telemetry Tab.

Comms Tab:
-new checkbox 'Enable on non-MP3X' in COM2/RADB section to enable COM2 on non-MP3X firmware
-new checkbox 'Process All Links' to allow the autopilot to process GCS packets from COM1/COM2 (RADA/RADB) regardless of which link is currently the active link

Telemetry Tab:
-new checkbox 'Disable standard telemetry on COM2/RADB' to disable the sending of standard telemetry on COM2/RADB
-new checkbox 'Disable user telemetry on COM2/RADB' to disable the sending of user telemetry on COM2/RADB
-new checkbox 'Disable camera telemetry on COM2/RADB' to disable the sending of camera telemetry on COM2/RADB

Datalog Viewer: added controls to 'Download Options' dialog to specify which autopilot port to override (COM1/RADA or COM2/RADB)

3.7.1346.0:
-datalog download API (via mpDatalogDownload) will now automatically unset [dontInitialize] to 0 upon finishing.
-datalog download API (via mpDatalogDownload) will now set [preventDatalogRecording] to 1 prior to downloading the log.
-datalog download API (via mpDatalogDownload) will now set [preventDatalogRecording] to 0 upon finishing.