CLOCK_MONOTONIC tmestamp from PRU

I am collecting data from the ADC using the PRU. I need to timestamp samples with sub-millisecond accuracy wall-clock time. My BBB’s system time is updated with a PPS GPS module, so it would be great to get the time from that (akin to clock_gettime(CLOCK_MONOTONIC, timer) call). Is something like this possible, and if so how?

Regards,
Istvan.