ppc405 dma - vm - cache question

Kate Feng feng1 at bnl.gov
Fri Oct 29 17:18:21 UTC 2004

gregory.menke wrote :

> Feng, Shuchen writes:

>> I do not know how well ethernet driver perform with non-cacheable

> Please ask this question more specifically.

Thanks.  It was not a question.  I meant I did not have to
write  the ethernet driver  accessing non-cacheable memory.
Thus I do not know the performance.

>> I really do not have the datasheet for the RTEMS motorola_shared BSP.
>> It could be that the firmware of thoses supported board already
>> had the hardware snoop turned on.  It would be better if you can
>> find out how to turn the hardware snoop on for your board.

>The motorola_shared bsp configures the system ram such that it can be
>the dma target or dma source, with a bus-mastering board on the
>backplane.  No additional hardware-level configuration is necessary
>unless you want the hardware to do something extra.  All PCI memory
>space is configured as non-cached, which I imagine is pretty much
>standard these days.  Nobody is putting system ram on the pci

I really never said that the system ram (SDRAM) is on the PCI backplane.
On my board, the 10/100MHZ ethernet driver (DMA) accessed the SDRAM,
which is cachable by CPU.   However, the firmware did not
turn on the hardware snoop.  For the PCI based 1GHZ ethernet, the
firmware had the hardware snoop turned on for  accessing the SDRAM.

However, I just found out from Gene that it's a custom board - no PCI involved.


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