I once used libparport -- a Linux library with hooks into kernel modules -- to obtain sub microsecond timing on custom hardware on a ~2008 Xeon pc. The parallel

I once used libparport -- a Linux library with hooks into kernel modules -- to obtain sub microsecond timing on custom hardware on a ~2008 Xeon pc. The parallel port has, by modern standards, terrible bandwidth but excellent latency: I waited for an interrupt and then "did a thing" once it was sent. I remember testing the timing with a 500 MHz scope and realising that I couldn't actually measure the timing error or delay accurately once I'd calibrated the whole system. The parallel port was basically wired as a general purpose ADC and DAC accessible by DMA, as the parent here says. Amazing kit at the time, and free in the context of expensive ADCs requiring custom hardware and difficulty interfacing in comparison.