> --- Ursprüngliche Nachricht --- > Von: Gabriel Paubert <[EMAIL PROTECTED]> > An: Gerhard Pircher <[EMAIL PROTECTED]> > Kopie: [EMAIL PROTECTED], debian-powerpc@lists.debian.org > Betreff: Re: Not coherent cache DMA for G3/G4 CPUs: clarification needed > Datum: Fri, 21 Apr 2006 00:07:08 +0200 > > More details please what are the exact capabilities of the south and > host bridges? The southbridge is a VIA82C686B, which supports ISA DMA in the first 16MB. The host bridge is a MAI ArticiaS. The ArticiaS has a bug in the snoop signal logic and therefore does not support cache coherent DMA.
> I've never needed (and therefore) used floppy on my PreP boards (Motorola > MVME2[467]xx series), but they have a south bridge (WinBond) that has 32 > bit DMA capability. This was specified in the PreP spec. Oh, I thought PReP specifies only 24bit DMA. Okay, so the AmigaOne is more like the i386 platform, just with a PPC cpu. ;-) > This may also depend on the host bridge since RAM appears at 2GB on > default PreP machines, which is an area that you can't access with > normal ISA DMA anyway. On the MVME machines, you could map PCI addresses > 0-16 MB anywhere in RAM by reprogramming the host bridge. This is not the case for the AmigaOne. The RAM starts at physical address 0 (similar to CHRP). AFAIK the host bridge does not allow the remapping of the address space. Maybe the southbridge can do this for DMA operation. I have to investigate this. Thanks for the hint! > > 3. How are DMA buffers used outside the kernel? Do user programs get a > > pointer to the DMA buffer (in theory) from the device driver or is the > > data copied to another buffer allocated by an user program? > > If your memory is uncacheable, you are better off copying it to > cacheable memory. At least you are sure that you only access it > once (trying to copy with FP registers to halve the number of > accesses might be a big win, but you need to be careful). Sounds like a big performance loss. I hope this is not necessary. Thanks, Gerhard -- GMX Produkte empfehlen und ganz einfach Geld verdienen! Satte Provisionen für GMX Partner: http://www.gmx.net/de/go/partner -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
