There’s a semi-wellknown trick on the raspberry pi for performing high-bandwidth and high-precision (in time) operations on GPIO pins from userland, using the D

There’s a semi-wellknown trick on the raspberry pi for performing high-bandwidth and high-precision (in time) operations on GPIO pins from userland, using the DMA engine. You keep an in-memory buffer of the next few milliseconds of bit patterns you want to write to the memory-mapped GPIOs and then just leave the DMA engine endlessly copying data from this (circular) buffer into the GPIOs. But crucially, you “pace” the DMA transfer by configuring it to alternate between copying a word to the GPIOs and copying a word to some other peripheral that you’ve clocked at a specific rate (e.g. the audio DAC, which won’t acknowledge each write until it’s converted the previous one). This lets you define the state of the GPIOs as an arbitrary waveform sampled at some frequency of your choosing, which is a crazy powerful tool for e.g. motor control (that’s what the Printipi 3D printer does) or bitbanging communication protocols, etc. You can also flip it around and sample GPIOs at close to 1 MHz. Piscope is an example of that. Once you start pushing 1 MHz, jitter starts to become nontrivial as you’re saturating the bus or competing with other memory transfers. So yes: a capable DMA controller can do some pretty mind-blowing things!