repl prompt on STM32H7A3. Working towards getting 8 mbyte ram on stm32 micropython.
```
MicroPython v1.13-237-g8db488963-dirty on 2020-12-07; DEVEBOX STM32H7XX with STM32H7A3
Type "help()" for more information.
>>> import gc
>>> gc.mem_free()
999584
```
https://github.com/koendv/micropython-spiram