On 16-4-2014 18:31, Lenny wrote:
Hi,
I started using the Multiply-and-Accumulate module of the PRU of my
Beaglebone Black to construct a real-time digital filter. But as soon
as I insert an instruction of the type, with any data or any of the
MAC registers (r25-r29) in the code, I induce some non-negligeable
latency.
MOV r25,0x00000000
XOUT 0,r25,1
I would estimate that the XOUT or XIN instructions cost about 5
microseconds, that is something near 1024 PRU clock cycles. I have
observed other awkward behaviour of the Multiplier module, for example
it only properly multiplied the values in registers r28 and r29 when I
did a XOUT 0,r28,8 instruction before reading the result. Does someone
have experience with this module? Is it possible that I am using it
wrong, that it has to be activated properly before being usable, or
that the hardware is not working correctly?
Thanks for any help!
Lenny
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Something is definitely wrong with your setup. I'm using the multiplier
for my BeBoPr stepper driver and IIRC the instruction takes only one PRU
cycle.
There's some overhead for set-up and to check the flags, but certainly
nothing like you're mentioning.
-- Bas
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