Over the winter, I worked with Howard Dutton, the author of OnStep Telescope Controller, to make it work with the low cost STM32 ARM Cortex M3 microcontrollers. This involved writing a hardware abstraction layer (HAL), so adding different architectures in the future would not be too hard, as it was.
Now, I have tested two different STM32 boards with OnStep, and they do work except for the EEPROM emulation in Flash. The solution is to use a low cost $1 DS3231 Real Time Clock (RTC) that has an I2C EEPROM on it. Still waiting for delivery.
Here are a few of vidoes demonstrating OnStep on STM32, as I progress through building a controller using STM32:
First is OnStep on USD $2.50 'Black Pill' STM32 . This is an ultra low cost 72MHz 20KB RAM, 128KB Flash stick based around the medium density STM32F103C8T6 MCU. It is equivalent to the Teensy 3.2 that is used in the MiniPCB, and should have enough pins for two axes (RA/DEC, or Alt/Az), USB, WiFi, and an ST4 guiding port.
Another is about the CZ Mini. This is a USD $12 (plus shipping) board based on the STM32F103VET6 high density MCU. It is similar in cost to the Teensy 3.2, and runs at the same 72MHz, but has more RAM, and flash (64KB of RAM, and 512KB of Flash), and plenty of pins. Apart from the lower MHz, it can be used for building full featured controllers, with 3 more axes for focusers and rotators, just like the MaxPCB.
Yet another video showing motors moving at different speeds for Goto and for sidereal tracking. Also, in the video is a comparison between the DRV8825 and the LV8729.