PRU number of cycles per instruction am335x

Christopher Piggott


l1:
        // Increment r1
        ADD r1, r1, 1

        // Store the new r1 value into the address pointed to by r2
        ST32 r1, r2

        // loop
        JMP     l1

The above code seems to take 4 cycles per loop, not three.  (The ST32 is really "SBBO    src,dst,#0x00,4").

What takes the extra cycle?  Is it the jump?  The TRM doesn't seem to publish instruction cycle information, probably because all but a few of them are 1...

--Chris

over 13 years ago

0 Maneesh over 13 years ago

TI__Intellectual 1835 points

Number of cycles for SBBO is 1+WordCount. So, that is two cycles in loop above. ADD and JMP are single cycle each.

If the target is a memory location, depending on the memory location on/off the chip, it could also take longer than a cycle because of bus interconnect latencies and arbitration times.

LBBO,LBCO take 2+WordCount cycles.

SBBO, SBCO take 1+WordCount cycles.

All others except SLEEP take single cycle. SLEEP can take from 1 to infinite cycles.

Thanks.

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PRU number of cycles per instruction am335x