I believe I found a way to use just an ESP8266 module to control a set of 3D printer stepper drivers directly. This code demonstrates how.
Background:
Other projects show how to use ESP01 as a wifi-serial bridge to the arduinos, but serial is still a bottleneck and wifi uploads are impractical.
Altough ESP8266 does 160MHz at 32bits processing (versus 16MHZ 8-bit from most Arduinos) it has insufficient realtime GPIO for controlling printers.
Raspberry pi shared the realtime gpio limitation, but wallacoloo still did reprap control using DMA. Nice! https://www.youtube.com/watch?v=g4UD5MRas3E
CNLohr did a really cool WS2812 led driver (weird one-wire serial protocol) using ESP8266 I2S audio output and DMA. https://www.youtube.com/watch?v=6zqGwxqJQnw
I2S and SPI look very much alike, and SPI can control shift registers. Hey! Opportunity!
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