Progress PI Zero Flight controller

I have BetaFlight ported to the PI Zero, but opted to move to CleanFlight due to the latest code check-in.  There are several APIs that are abstracted to make porting to Linux easier. The basic idea is to use LINUX #define to comment out micro-controller specific code and add XXX_linux.c drivers for SPI, I2C, serial, pwm, etc.   Still going to stick with boost ASIO for scheduler, still based on timers (timerfd). 

The SPI communication to the GD32F1 is progressing:

• GPS handling, moved baud rate, GPS update rate to GD32F1
• Simplifies command/processing and speed
• Working on PWM decoding (PPM/PWM)
• Working PWM encoding 4 outputs

Have SPI working with MPU-9255 at 8Mhz from the PI Zero.  

Still pending:

• Cannot find any more "red" GD32F103 board might have to move to another board
• Transmitter
• Turnigry 9xr pro?
• Radiolink at 10
• The main difference between the two are:
• Telemetry s.bus vs i2C 
• Have to buy another receiver Radiolink to have s.bus and i2c telemetry (R9DS) which is another $13.
• Radiolink is not open source but many ports and docs on decoding i2c for telemetry. 
• Radiolink has sliders 9xr pro does not
• HK shipping costs and pricing changes. 
• Thoughts?