Hi @Fredd ,
what I always does is working with the internal timer of the pru.(https://community.element14.com/products/devtools/single-board-computers/next-genbeaglebone/b/blog/posts/beaglebone-pru---timer-functionality)
The internal PRU cycle is 5ns so you need to sum the current timer value + loop timer and inside the loop control the comparison of the current timer value X your variable.