I wanted to try to pitch this idea again:
make a CPC "hat" (MX4 connector of course) with two or three "slots", one for a
dirt cheap STM32 mini board such as
https://www.amazon.com/Aideepen-STM32F103C8T6-Minimum-Development-Learning/dp/B078KFK12V (https://www.amazon.com/Aideepen-STM32F103C8T6-Minimum-Development-Learning/dp/B078KFK12V)
and then, 1 or 2 mikroBUS slots for click! boards:
https://www.mikroe.com/click (https://www.mikroe.com/click)
In addition, a couple of IO headers (more or less direct pass-through from the STM32 board).
That could be dirt-cheap, and quite versatile too. (OK, some click! boards are a little bit more expensive, but all you really need is ONE click! board to get started, and the STM32 board).
I am not saying that I would make such a "hat" board, but I would buy one if somebody did :)
Following points:
- no additional hardware required on that "hat" board (maybe level shifter / converter, ok - but that's it - the Cortex M3 @ 72 MHz is fast enough to do all the CPC address bus decoding etc. on the fly, no CPLD or such required)
- great software development IDE for writing drivers and firmware for the Cortex; easy to program, just need a USB cable AFAIK (no programmer required)
- cheap enough (2 for 13 $!!) such that one can just have a couple of pre-programmed STM32s lying "around" - just plug and play with click! boards
- click! boards are available for all kinds of purposes (MP3, RTC, Sensors, HCI, SDCard, ...)
- make the STM32 / Cortex M3 firmware "HEX" files open source in a central GitHub such that people can develop drivers and share them for the different click! boards
- the PCB development will be almost trivial - just level shifters and PCB traces and pins, basically! No further components required (ok, maybe a reset button and 2 LEDs).
- no "year long" development cycles for new hardware required
The "first firmware" for the SM32 will of course have to demonstrate how to communicate with the CPC (address decoding and such), how to do SPI and I2C with a clikc! board, and so on. After that, developers are good to go!
Just saying, I have no affiliation with MikroElektonika whatsoevery, but their mikroBUS! standard and click! boards are just to ingenious to ignore :)