Hurdles of mating M17 with MD380

We have been trying to check if M17 can be implemented on MD380-class radios. Many thanks to the OpenRTX team for helping us with that one.

Let me list all unsolved mysteries and some other problems.

  • There’s no microphone audio signal present at the microcontroller (ADC)
  • PC8 pin, that’s probably configured as a PWM, is lowpassed and fed into speaker amp - is that enough to get speech out?
  • 2-point modulation is done by the HR_C5000 chip. We can only try and set offsets at both outputs by writing to specific registers. That in turn allows us to swing MOD1 and MOD2 only by about 850 mV. Is that enough to get M17 RF out?
  • How to get demodulated data?

I think it’s a great idea to see if the hardware can be pressed into service. Mobilink mentioned that the DMR deviation is less than that specified by M17, and that we may not be able to get the full spec’d 2400Hz deviation. I’m rather new to this so I can’t comment on how problematic that might be, I’m mostly throwing that in here for the sake of documenting things.
It might be worth exploring whether we can shoehorn our own guts into the MD380. It’d save effort on enclosure design, but it really depends upon how much real estate is available inside of the MD380. Either way, I’m all for piggybacking on someone else’s work if it saves us time getting some good hardware up and running.
My only reservation about relying solely upon the MD380’s hardware is that it makes us dependent upon availability of something that’s ultimately closed-source.
How far have reverse-engineering efforts on the MD380 progressed? Is it documented anywhere?