Less than 1us is relatively straightforward on an embedded system. My application was simulcast for a software defined radio. It was running on a TMS320 DSP (

Less than 1us is relatively straightforward on an embedded system. My application was simulcast for a software defined radio. It was running on a TMS320 DSP (192MHz) with DSP/BIOS as the operating system. Timing was driven by a GPS 1PPS pulse connected to an interrupt pin. The absolute response time was around 100ns and repeatability was of the order of 10 nanoseconds (dominated by the drift between the 1PPS and the processor's clock).