DisplayPort OSD Framebuffer

This takes Betaflight MSP DisplayPort (so-called "canvas" although this is a misnomer as there is another Betaflight "canvas" mode for Pixel OSDs) messages through UDP and, using a font provided at font.bin, renders them to a framebuffer.

SFML and DJI viewports available, as well as a mux which creates a pty and provides filtered MSP access, and reroutes DisplayPort messages to UDP.

To build for DJI, install the Android NDK and add it to your path, then use make -f Makefile.dji .

To build for UNIXes, install CSFML and make -f Makefile.unix .

Provided targets and tools are:

• msp_displayport_mux - takes MSP DisplayPort messages, bundles each frame (all DisplayPort messages between Draw commands) into a single UDP Datagram, and then blasts it over UDP. Also creates a PTY which passes through all other MSP messages, for dji_hdvt_uav to connect to.
• osd_dji - Listens for these MSP DisplayPort messages over UDP and blits them to a DJI framebuffer screen using the DJI framebuffer HAL libduml_hal access library, and a converted Betaflight font font stored in font.bin .
• osd_sfml - The same thing as osd_dji, but for a desktop PC using SFML and bold.png .

Installation

On Air Unit / Air Unit Lite (Vista):

adb push msp_displayport_mux /blackbox
setprop dji.hdvt_uav_service 0
mv /dev/ttyS1 /dev/ttyS1_moved
nohup /blackbox/msp_displayport_mux 192.168.41.2 /dev/ttyS1_moved /dev/ttyS1

This tells the displayport mux to send data from /dev/ttyS1_moved to 192.168.41.2 (goggles) and to create a fake serial port at /dev/ttyS1 with the displayport messages filtered out.

Now you can try setprop dji.hdvt_uav_service 1 - depending on your FC it may or may not be able to handle the volume of MSP messages as well as DisplayPort at the same time.

On goggles:

adb push osd_dji /blackbox
adb push font.bin /blackbox
cd /blackbox
nohup ./osd_dji &

Hold the BACK button for 5 seconds. You should see the DJI UI disappear and be replaced by the MSP OSD (or at least a WAITING message at the bottom of your screen).

To restart the DJI goggles, hold the BACK button for 5 seconds again.

Rebooting will kill the process and return the goggles to "normal."

Enjoy.

FAQ / Suggestions

• Why can't we keep dji_glasses (the Goggles UI) running while we render the OSD?

Access to the DJI video driver is exclusive. We'd have to build some kind of userspace frame-buffer sharing system to get this to work. The dji_glasses system uses DirectFB which provides this on paper, functionality, but the DJI backend driver as well as the overall stack aren't configured to use it properly.

• I can't change channels / see my bitrate / record video / etc. while the overlay is running?

See above - dji_glasses has three primary purposes: turning user input into commands for the radio/CP layer, displaying UI, and, for whatever reason, recording video. Without dji_glasses running we will have to replicate these functionalities.

Additional Reading / Learning

https://github.com/fpv-wtf/margerine/wiki

Shoutouts / Thank You

• http://github.com/fpv-wtf team, for making this all possible and very helpful random bits of advice