Just for the sake of anyone trying to do this in the future.
The bus throughput increased significantly by using memcpy() C library function. (I am using Windows CE 7).
Here are the details for my setup
- Win CE 7
- iMX51
- Asynchronous mode on WEIM CS0
- WWSC set to 32 WEIM Clock cycles.
- When I was using a for loop to send out 16 bit words on the WEIM Bus:
So when I captured this waveform, I was sending out 4 words (16 Bit, DSZ).
Time taken in the transfer is around 2 micro-secs, throughput 32 Mbps (32Mbps).
There is a huge dead time of around 180 nanoSecs between two successive writes.This dead time was a pain because I could not find any configuration in the WEIM Config registers that could be used to change it. I tried reducing WWSC from 32 to 8, this reduce the CS assertion time, but the CS dead time remained stuck at 180 nano-secs.
Because of this I was considering if by using assembly instructions STM instructions to increase the throughput. In the meanwhile I came across a thread on windows embedded compact forum, Alternate-of-memcpy, in which Bruce Eitman advises that the memcpy is already implemented to copy data in the fastest possible way. So I guessed the memcpy would already be doing what I was planning to using using assembly, I changed by implementation to use memcpy instead of the for() loop. The results have been very positive. - WEIM bus timings after changing the implementation to use memcpy()
Time taken for the 4 words transfer is 1 micro-sec, so the throughput is about 64Mbps (doubled, but still not good enough).
On changing WWSC to 16 WEIM clock cycles (from 32), the throughput increased further:
32 words(16 bit) transferred in 4.9 micro-seconds, throughput of 104 Mbps.
The throughput can be increased further by reducing the WWSC value.
We are working on the Burst mode writes, but not through with it yet and we are expecting a much more increase in throughput based on Yuri and Igor's inputs. We are trying to achieve a throughput of around 350 to 400 Mbps.
Conclusion is, in windows CE 7 the memcpy can help increase your throughput on the WEIM bus, maybe before going into assembly you could give it a try.
