This is the firmware for the FlexTrak board:
https://store.uputronics.com/index.php?route=product/product&product_id=118
See separate FlexTrak repository for the Pi host software in Python:
https://github.com/daveake/flextrak
For documentation on this firmware. the Pi host software, and the serial protocol that they share, see the FlexTrak manual:
https://github.com/daveake/HAB-Documentation/blob/main/FlexTrak%20Manual.pdf
V1.22 - Added option to send the field list
V1.21 - Bug fix - saved settings not being loaded from flash.
V1.20 - Reduced RAM footprint. Reset radio on startup. Default 434.225MHz Mode 1.
V1.12 - 6 custom host-populated telemetry fields, cutdown, LoRa uplink
V1.01 - Host priority mode, ability to fake GPS from host (for replaying flights)