But on a pi, how accurate is the CPU and gpio speed? On an Arduino mega it's guaranteed to be 68.5ns give or take a tiny amount because that's how long an instruction takes for gpio bitbanging registers. This makes it possible to interface with hardware that requires this precision timing. On a pi even if you're at 700mhz constant clock, caching supposedly will mess up your timings for gpio. On top of that I haven't seen much in what the lowest stable delay is for the pi gpio.