Help needed the OpenGD77 “Hotspot mode”

posted in: DMR, GD-77, Ham radio | 4



The OpenGD77 project is massive undertaking and if possible I’d like to get some help from the readers of blog on a wide variety of related topics.

Top of my Help wanted list is for the Hotspot mode which we hope to develop for the OpenGD77


Hotspot mode will allow the GD-77 running the OpenGD77 firmware to be connected to a PiStar device, via USB using its programming cable, to act in the same way as the simplex MMDVM “Hat” board – For DMR only


I have analysed data serial data protocol between MMDVMHost and the MMDVM_HS firmware running in the “Hat”, and I understand the general protocol, and will soon start to write the initialisation and some other communication functions.


However, the actual DMR data traffic between the MMDVM_HS and MMDVMHost looks nothing like raw DMR data 🙁


MMDVM_HS seems to do some strange bit swapping processing of its internal DMR data before sending it,via Serial, to MMDVM_Host, but I don’t know what the internal data inside MMDVM_HS looks like, unless I recompile it and add some debugging statements to write the data out to the Nextion port and then connect that port to my PC via a USB.

This is a lot of additional work and will take quiet a lot of time simply to setup to compile MMDVM_HS on my RPi etc


I’ve tried to contact Andy CA6JAU who wrote MMDVM_HS to ask for information on the internal DMR data format in MMDVM_HS, but I’ve not been able to contact him, I’ve also tried to get in contact with Jonathan G4KLX for help from the MMDVMHost side of things, but not had any luck with that either.


I’m sure we’Il will eventually be able to get this working, but I don’t have any detailed knowledge of how MMDVMHost or MMDVM_HS work, and potentially it may not be possible to interface the OpenGD77 firmware with the normal version of MMDVMHost and we may need to develop a modified version.

If we needed a custom version of MMDVMHost it would be more difficult for people to use the entire system, because they’d need to run a custom version of PiStar, which could then not easily be updated, unless Andy Taylor could be persuaded to include a custom version of MMDVMHost in PiStar for the OpenGD77…


So I’d like to put a general call out for anyone who could give use some ideas about which approach we’d need to take in order to get Hotspot mode working as soon as possible.


4 Responses

  1. Shawn

    I would like to help. I have read and mod the MMDVM firmware/host software in the last 12 month and learned a lot from that.

  2. Roger Clark


    I replied to your post on github.

    I’d love to just process the raw data from MMDVMHost as it would mean that people don’t need to change PiStar to use Hotspot mode

    But the impression I got from everyone I discussed this with, including Jonathan G4KLX was that I would need to modify MMDVMHost, because the data that was being sent was not going to be usable.

    Hence I started to go down the route of writing to modify MMDVMHost.

    I have VS2017 installed on my PC and can compile and run MMDVMHost and I have a Zumspot libra connected to my PC to observe what the data looks like etc etc

    So I’ll take a look at samplesToBits() to see what that does, and whether its possible to do the reverse, and perhaps reverse the other layers in MMDVMHost to get back to the raw data without all the sync etc etc etc bits

  3. f6ggx-32Sylvain

    hello Roger, I tried to install your version on my TG77 which currently works official version 3.1.6 radioddity.

    at the end of the load, (98%) The green cursor stops and asks me to reboot the tg77.
    I don’t know how to do this reboot and finish the update.

    After turning off and turning on the TG77 the screen is well modified.

    Then when I want to download or read my codeplug I have an error message that prohibits loading.

    same if I want to read the configuration of the TG77.

    Thank you for your help.
    Kind regards. Sylvain F6GGX

  4. Roger Clark

    post to

Leave a Reply