Peter wrote:
Both variants of GDL90 (the broadcast one, or the FF/Ipad unicast one) use 0-255 for the 0-359 track angle.
FWIW, Connext broadcasts track angle as `i16` with a conversion factor of * 360/65536 to get the degrees. Or as `f32` directly in degrees. It depends on what channels a particular avionic device supports.
I did a quick search.
ForeFlight consumes GDL90. Garmin’s apps (Garmin Pilot) consume Connext.
So one could radiate both concurrently, for whichever app is being used.
The problem AFAIK is that Connext is Garmin proprietary and licensed under an NDA. So it is a dead end.
Peter wrote:
ForeFlight consumes GDL90. Garmin’s apps (Garmin Pilot) consume Connext.
ForeFlight can also consume Connext; the real problem is that it can only do so via Bluetooth RFCOMM, and so thanks to Apple, you must support iAP2, otherwise it just won’t bond with your device.
Peter wrote:
The problem AFAIK is that Connext is Garmin proprietary and licensed under an NDA. So it is a dead end.
Well, the vendor extensions that ForeFlight uses are just as proprietary as Connext, aren’t they? … and having implemented a Connext SDK myself, it’s quite amazing how much you can infer from the wire.
Is there any point in the FF GDL90 extensions?
I am not implementing BT as well as WIFI 
Peter wrote:
Is there any point in the FF GDL90 extensions?
I haven’t looked into them (yet?), so I can’t tell, but from the practical perspective, this would allow you to talk to Sentries. You can check this article out for some background:
https://cbpowell.wordpress.com/2025/09/25/reversing-the-scout-ads-b-receiver-part-1/
Peter wrote:
I am not implementing BT as well as WIFI
Sadly, Connext over WiFi is locked into Database Concierge mode on the device side, so you can’t use WiFi for normal data streaming. It might be possible to convince them otherwise, but I haven’t looked into that.
This was fun to do
Simulated AHRS data going to Foreflight on Ipad, via GDL90.
The LCD is 320×240, ILI9341, driven at 11.2MB/sec over an 8 bit parallel bus, from an STM32F437, 168MHz. Both GPS and attitude data are being sent.
The LCD shows a KI256 emulation, complete with the Flight Director command bars.
Graphics generated directly from trig functions, in C, using the 437’s hardware floats which do single precision float ops in 6ns – roughly the speed of a Cray 1. A sinf() is under 1us.
The GDL90 supports both the common multicast UDP and the Foreflight-specific unicast UDP. The latter offers no obvious advantage in performance or accuracy.
