Liu Dave-R63238 wrote:
According to Ira, the DMA method was faster than the cpu method: "It makes the DMA initialization normal speed again. The DMA in the for loop takes the longest (as expected).
So yes, strangely it (enabling the icache) makes a HUGE difference. The total time is <3 seconds now. It is now faster than the previous CPU method."
Logically the DMA method should be faster, and Ira's results seem to reinforce this. I don't have an 83xx board to test on, so let me know if others have different results than Ira.
I did the DMA init test with the orignal DMA code. At that time The DMA method is slower than CPU method. Strange why the result is different.
Instruction cache enabled/disabled is the difference - it eliminates instruction fetches from competing with the DMA engine on the SDRAM bus. See my recent message: http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/63152/focus=63308
FWIIW, in our experience with various PowerPC processors, using the CPU's "dcbz" (data cache block set to zero) instruction is also very fast, but it only works if you want to initialize memory to zero. You need to enable data caching (obviously) and not having instruction cache enabled would cripple that method too.
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Best regards, gvb