A post from Jim Ki6ZUM the designer of the current MMDVM Zum board... in response to the demise of the Ardunio Due...platform and a replacement platform
I'm very please to see all the interest and enthusiasm for the STM options. As I mentioned in an earlier post, there's been a lot of work going on in the background. I too would like to be able to sunset our reliance on a discontinued board.
The Mbed environment is not my favorite platform, especially because it uses an online compiler. Lately I've been having a lot of trouble with the difficult "error 230" which basically means you are out of luck compiling until you come back later. I also haven't had a lot of luck exporting the project so I can use an offline compiler. I've also spent quite a bit of time trying to work around the the issues with how they do ADC. I gave up quite a while ago.
I'm attaching a couple of pictures to show how I've been doing my testing. The first one just shows that I've using an STM32F4Discovery board that I jumper to a Papa prototype board, and connect to the PC via an FTDI adapter. Getting the VCP interface has been fruitless so far.
The second picture is an early prototype of a Pi adapter board. It is using the STM32F405 chip. It was originally designed when I thought that the Pi Zero was going to become easily available soon. I'm afraid the Pi Foundation isn't putting a lot of effort into producing them now that they've released the Pi 3. It is a bit of a problem in that I can't actually buy any new Pi boards at the moment from any of the official US distributors.
Based on the feedback so far on the boards from Bruce, it doesn't look yet like there will be too many hardware changes to the basic MMDVM radio interface design. There are a few other changes that will be included in the next Pi prototype, including probably abandoning the Zero footprint.
For those who would like to help get the STM code working, I'd recommend looking at the F4Discovery board. It is cheap and it works well. It is a fairly new board so I'm confident it won't be discontinued any time soon.Since we are a long way away from being able to offer the Pi boards for sale, you'd need to use the Discovery board with an existing MMDVM board (similar to the attached picture). A lot of thought and testing has gone into the selection of the F405 chip, but I'm open to discussion about other parts.
As far as software development goes, I have several failed attempts with various development environments. I'll try to publish soon some of what I've managed to get working.
Things are moving on nicely. A number of repeaters have opened up with the MMDVM, usually as DMR only, and I think many more are on their way. I would imagine that the number of MMDVM systems could top the 100 mark within a few months.
For the most part development is now slowing down, due to the various elements reaching maturity. So here is the status of each major component:
D-Star. This is pretty well complete and some serious bugs squashed within the last few weeks. The host D-Star repeater is simpler than the D-Star Repeater, but that’s fine by me as the original repeater software has become rather large to say the least. It’s possible/probable that some of the extra functionality of it will migrate over to the host, but I’ll be careful about which parts.
DMR: This has been the most fun to implement, lots of interesting and varied techniques to learn and use. The DMR side is pretty well complete. The only known missing part is the regeneration of ¾ rate data, so if anyone can give me some pointers as to how to progress I’d appreciate it. I can probably do the encoding, but decoding has me baffled.
Fusion: This is a mess. The more time I spend with it, the less enamoured with it I become. The host is RF only, and I don’t see that changing in the foreseeable future. Fusion has some great ideas, but most of it is pretty poor, and doesn’t lend itself to network transportation, unless you exclude VW mode, which would be a shame. I consider Fusion to be a curiosity! Any help in regenerating the audio would be appreciated. I think I have the callsign part correct, but I’m not sure.
Modem: Apart from supporting the STM32 series of chips, the only enhancement planned is to allow the MMDVM to co-operate with another repeater controller to form a multi-mode repeater (i.e. FM + MMDVM). This will include adding two new pins, one would be an MMDVM “I am busy” pin, and an input from the other controller to say that it is busy and the MMDVM should not operate. In later boards these pins will be added, but in the interim I have a quick and dirty solution. For a DMR only MMDVM, you can use the transmit out line to lock out the other controller, and I will add a compile option to allow the currently unused COS input to be used as the MMDVM lockout input.
Display: I will add support for other displays in due course, it’s a matter of identifying suitable ones that are cheap. The currently selected Hobbytronics display isn’t cheap, I know, but it fits the bill nicely. I am sure others will too.
Yes we know that some people have been having "issues" with the JST-6 connector. smile emoticon :-) When the next batch of boards ships around 12th March we will be including a small cable (see picture below) free of charge. This might slightly increase the mailing cost for people that are ordering multiple boards.
I want to be fair and am offering the same to the people that have already been shipped boards , Please contact me at email@example.com