Fastest way to read ARM cycle counter into PRU

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1

Hello,

I need to synchronize some actions on arm and pru and therefore need the fastest way to read the ARM cycle counter into the PRU.

I basically want to match up the PRU cycle counter and the ARM cycle counter. Am I right when I assume the ARM cycle counter runs exactly (PLL phase locked) 5 times faster than the PRU’s?

So I want to catch some GPIO event (gps pps) on the PRU and tell the ARM core in a scale of a few nanoseconds when it occured on his time scale.

When ignoring overflowing 32 bit counters my pseudocode would be:

  1. PRU waits in the initialization process to receive the ARM cycle counter

  2. Write ARM cycle counter into PRU-DRAM

  3. PRU sets his own counter to this value divided by 5 (+2 for the ram read and register write)

  4. PRU waits for GPIO event

  5. On GPIO event save own counter state, multiply by 5 and message it to ARM

  6. ARM compares his cycle counter to the messaged one and knows when the GPIO event occured

Any thoughts how to improve?

Thanks, Steve

2

Maybe just a single question instead of the above:

=> Can the PRU read the ARM cycle counter directly or predictably?