Tx may be possible but not Rx, because there is no direct audio path from the AT1846S FM TRx IC to the CPU
No one had time to try to write code to test whether the hardware, is capable of generating the audio tones needed for 1200 baud.
The radio hardware is not designed for this purpose, so no one knwos if this is possible using the tone generators in the AT1846S or HR-C6000
It is not possible to write firmware based on a video teardown
This is a non-commercial open source project. The team members are using their spare time to participate in the project.
If you are interested in porting a new model, you can reverse engineer the related model , and feedback the technical details obtained to the team, so that it is possible to make effective progress.
I own one DM-X radio (DM1702) and if I can make an OpenGD77 version for this model I will be happy to test it.
I realize that it's a long way to go to make OpenGD77 for this radio and it requires a lot of work and may not succeed
but I keep my fingers crossed and wish Amo good luck
The firmware encryption also needs to be cracked
I did a quick search and found this
But I can't see any encryption key data
I also checked RadioTool https://github.com/v0l/radio_tool
but it does not support the DM-1702 / DMX
If you are serious about porting to this radio, I'd recommend you first find all possible versions of the manufacturers official firmware and start to analyse those firmware files.
They will be encrypted, but often the header can be identified because it may be the same for all firmware versions.
The TYT radios like MDUV380 and MD9600 and the DM-1701 effectively use the same key for all firmware versions, but the GD-77 doesn't exactly do this
The GD-77 has an additional value obfuscated in the header, which is different in each firmware version, and is a seed into the encryption table. This made it much more difficult to Kai DG4KLU to originally crack the GD77 firmware encryption
You'll also need to understand how the firmware is loaded into the radio. i.e in bootloader mode is it a STM DFUSe device like the STM32F405 based radios, or is it a custom bootloader protocol.
It seems that most STM32 based radios use a modified STM DFU bootloader with encryption / decryption added, but this does not seem to be the case for MK22 based radios