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.