Just a basic bit of Linux C to drive the kernel SPI driver enough to get pixels onto a PCD8544 display (commonly called the Nokia 5110 Display).
I was able to refer back to code I wrote in Forth(!) in 2016(!) to help. Thanks, past Aaron.
Despite being quite a short program, this took hours of debugging and I ended up having to break out a signal analyzer. I made numerous simple errors throughout, but a special shout out goes to confusing GPIO pin numbers with P1 header pin numbers more than once.
I shell out to raspi-gpio for the non-SPI parts. It seems in 2022 my options for doing this in C without forking mostly relate to poking inside /proc/mem or importing a big library that defeats what I'm trying to do (lower level C development).
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