Reduce PRU DDR read latency

David Gesswein

I see up to 5.8 microseconds of latency when the PRU is reading from DDR memory. Is it possible to reduce this? I tried changing registers that looked promising for giving the PRU priority but they didn't have a noticeable effect. This is running on a Beaglebone black,

The examples I found for doing DMA from the PRU were all for older kernels and wouldn't work with Linux 3.8.13. Is there an example I missed that works with this kernel?

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

Hi David,

Kernel 3.8 is a community project that's supported on http://beagleboard.org/Community/Forums . Please ask there.

0 sviss over 10 years ago

Expert 1530 points

I do not understand what is "read from DDR memory". I use to write the DDR from PRU. Unsure what is the exact latency but it definitely times less than 5 microseconds.

0 David Gesswein over 10 years ago in reply to sviss

Prodigy 20 points

I was using a PRU timer to measure the maximum time a LBBO from DDR takes while the ARM is busy. It looks like PRU writes are posted so instruction execution can continue while the write completes therefore are much faster. Reads block execution till the data returns.

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Reduce PRU DDR read latency