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why EDMA no speed improvement

Started by Yong Yang ●May 14, 2004
Hi, all
 
I compared EDMA fast copy DAT_copy() with C function memcpy() in my program, but there is no difference in speed. Why does EDMA have no improvement of speed?
 
Thank you
 
Yong
Reply by Andrew Elder ●May 14, 20042004-05-14

Hi Yong,

TI has a great (if somewhat daunting) set of documents that should help you
answer this question.

Items to research
1) where are the source and destination arrays located in memory space ?
2) what is that access timing for those memory spaces from CPU vs EDMA (see
Peripherals Guide)?
3) how is your timing done - are you sure it is accurate ?
4) when is EDMA expected to be a lot faster than CPU copies.
5) is L2 cache enabled ?
6) what affect do you think L2 cache will have ?

If you can answer all the above, I think you will have answered your question.

- Andrew E. At 09:29 PM 5/13/2004 -0700, Yong Yang wrote:
>Hi, all
>
>I compared EDMA fast copy DAT_copy() with C function memcpy() in my program,
but there is no difference in speed. Why does EDMA have no improvement of speed?
>
>Thank you
>
>Yong >
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Reply by Mike Dunn ●May 15, 20042004-05-15
Hello Yong,
 
The purpose of DMA is not necessarily speed improvement [short DMAs can be slower] for a single function but to improve speed/performance in more complex situations.
 
How many additional instructions can you execute during memcpy?? [0]
How many additional instructions can you execute during and EDMA operation?? [usually > 0]
 
The more "move activity" that you perform with DMA, the more CPU cycles that you MAY [depending on memory bandwidth...] free up.
 
mikedunn
Yong Yang <y...@yahoo.com> wrote:
Hi, all
 
I compared EDMA fast copy DAT_copy() with C function memcpy() in my program, but there is no difference in speed. Why does EDMA have no improvement of speed?
 
Thank you
 
Yong


Note: If you do a simple "reply" with your email client, only the author of this message will receive your answer.  You need to do a "reply all" if you want your answer to be distributed to the entire group.

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