How to write a C-based module for CircuitPython #CircuitPython #Programming
A nice article by epxx.co, PU5EPX, explores extending CircuitPython with C. He wanted to hook a PS/2 keyboard to a CircuitPython board; the objective being to write a PS/2-to-USB converted in Python. The PS/2 wire protocol is similar to UART, though the wires are Data and Clock instead of TX and RX.
C code is fast enough to bitbang PS/2 in 8-bit microcontrollers, even though using interrupts to detect clock transitions is best, freeing the controller to do other tasks. Bitbanging in CircuitPython is basically impossible since it is not fast enough to find clock transitions at 20kbps speed (yes, I’ve tried). So we need to write a C-based CircuitPython module, and try to use interrupt-based clocking.
One issue of CircuitPython is, it can’t load an external binary module. Every binary module must be baked into the interpreter. (Since microcontrollers run code from ROM, I guess this won’t change in the near future.) In order to add your module, you need to build the whole interpreter and flash the board.
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