So, as I reread this and talked to others, it sounded like my request may not have been all that clear, so here's another go, more from application than technical function:
I usually am mobile while on ham radio (VHF/UHF). I just recently installed an FT-8900. In my area, due to terrain, 6m is used (and is occasionally the only reliable way to get out). Cell tower coverage is pretty spotty.
I'm looking to use an existing wide-area DMR repeater transmitting on actual ham bands at "repeater power" located on hilltops with wide range. I'm looking to do this mobile, where an HT would NOT cut it. I would rather not have two completely separate radios and antennas in my vehicle, and the only viable mobile I've even considered to this point is the Anytone 578. Unfortunately, even if I did go the dual-radio route, the Anytone does not allow for separating the control head, and that is required in my vehicle. So, that leaves me with no ability to use DMR when mobile, which is 90% of my ham radio activity.
What I wanted was a way to do DMR with my existing FT-8900, much like I can do 9600 baud packet with my FT-8900 by plugging in additional equipment to the jack on the back of the radio. I was hoping to create a "DMR TNC" with its own little display, mic, and speaker, and have it connect to my FT-8900 and use it as a CLIENT on the DMR system, and NOT need any internet in my vehicle (or immediate vicinity).
So, to accomplish this, I see:
1) there ARE software packages that can work with a Pi to connect via IP to the DMR network and run as a client (with a mic/speaker), allowing all talk group access,etc., available on the IP connection you are using. This is 1/2 of what I was looking for, but no IP connectivity to the DMR network...I want to use my radio.
2) there are solutions for using a Pi to connect to an analog radio and turn it into a hotspot/repeater and connect to the DMR system with IP. However, I am not looking to be a "repeater" (server) but a user (client).
Ideally, I would like to take parts from both of the above and "mash them together" so that my software frontend will interface with a board (perhaps like the STMDVM, perhaps just an ADC like NWDR's DRAWs hat) which will connect with the analog radio. Yea, I will likely need something like the ThumbDV or some other AMBE vocoder chip connected via USB....OK. The missing piece seems to be some sort of software bits to act as an RF client. I'm also wondering if this hasn't already been done because the analog radio cannot switch its transmitter on/off fast enough to do TDM as a client....If it actually isn't possible for this (or other technical reasons), please let me know!
One more thing: I am NOT limiting options to "ready built systems". I am a tinkerer, and I am good with linux. I'm sure I could get a DMR-AllStarLink system going or other such stuff. I'm not an outright coder, so modding the source code of the client to implement what I'm looking for is beyond me, but I don't require something as neatly packaged as PiStar (but would gladly accept it if it were there!).
Thanks again all!