Kasimir schrieb am Mittwoch, 12. Mai 2021 um 21:49:33 UTC+2:
> It works fine, only the delay time loop need better resolution, at the
> moment the time for only one loop is too long.
> Have no idea to optimize ist.
>
Twice as fast:
LOOP EndWait, R17.w0 // note: max 16 bit counter
EndWait:
> Also from
> or r30, r30, (1<<4) ; debug, trigger signal for oscilloscope
> to
> naechster:
> lbbo &r30, r15, 4, 1 ; (r15) = pattern
> I measure 250nsec ..... was expecting 25nsec .....
>
> I can see some jitter on my oscilloscope ( Tektronix THS730A ), has
> nothing to do with
> GND connection, long wires etc., all that is perfect. Oscilloscope works
> fine.
>
> Is it possible that "some what" from Linux / ARM area is disturbing my
> timing?
>
The LBBO &r30, r15, 4, 1 instruction needs at least 3+1 cycles (as long as
the adress in R15 is not in the PRU local memory map). And it may take
additional cycles in case of heavy trafic on the L3 bus.
Note: for cycle watching you don't need an osci. Instead you can use the CYCLE
Register (offset = Ch) in the PRUSS_PRU_CTRL register space.
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