Passing Mailbox messages between ARM and PRU

[FredEckert]

@Chris_Grey

Question though, I was trying to find something that seemed to be within the PRU subsystem. It seems all the documentation suggests that once the PRU has to reach outside the subsystem, there’s more than the standard opcode processing delay of 1-2 PRU clock cycles to complete, and the time it takes is also non-deterministic. Being GTC is “global”, are reads to it going to be subject to this non-deterministic delay?

I searched for some definitive information on this but, couldn’t find it readily. Based upon what I have gathered there is a “few nanoseconds of jitter” caused by going through the system interconnect. I also read somewhere that it can vary based upon the traffic on the interconnect.

Maybe this recent PRU timer post by user Juvinski could help you stay in the PRU subsystem:

Interruptions in BBB

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.