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Date:      Mon, 18 Dec 2000 15:20:16 -0800
From:      Randy Primeaux <randy@Cloudfactory.ORG>
To:        doc@FreeBSD.ORG
Subject:   Re: kernelconfig-config.html: ATA_ENABLE_ATAPI_DMA 
Message-ID:  <200012182338.PAA15231@relay.ultimanet.com>
In-Reply-To: Message from Brooks Davis <brooks@one-eyed-alien.net>  of "Mon, 18 Dec 2000 15:09:48 PST." <20001218150948.B10804@Odin.AC.HMC.Edu> 

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Brooks,
Thank you for your quick response.

I should have clarified that my local goal is to enable the "highest"
transfer rate available, given my mixture of hardware and software.

My global goal, is to see a comment for each option that alludes to
"why, or why not, you would want to enable this option".

I will ponder on your response, and see if I can come up with a
politicly correct comment for the Handbook.

I checked dmesg for my primary desktop and found:

ata0-master: DMA limited to UDMA33, non-ATA66 compliant cable
ad0: 29314MB <IBM-DTLA-307030> [59560/16/63] at ata0-master UDMA33
ad1: 516MB <IBM-DALA-3540> [1988/14/38] at ata0-slave PIO3
ad2: 7665MB <QUANTUM Bigfoot TX8.0AT> [15574/16/63] at ata1-master UDMA33
acd0: CDROM <CD-524EA> at ata1-slave using PIO3

I'll test tonight.

Thanks.



Brooks Davis writes:
> On Mon, Dec 18, 2000 at 03:04:12PM -0800, Randy Primeaux wrote:
> > The following entries are not clear to me, i.e. risk vs. benefit.
> > I have UDMA33/66/100 devices, and am considering enabling
> > ATA_ENABLE_ATAPI_DMA on a pci bus.
> 
> Many stupid ATAPI devices (CD drives, ZIPs, etc) claim to support DMA,
> but crash your system if you try to use it.  Thus you can't turn this on
> be default.  It's worked for me on some systems, but there is no list
> of working devices and it's unlikely that one will ever exist given that
> CD drives are pretty much commodity devices and thus there's a lot of
> junk out there.  This doesn't belong in the handbook, IMO.  If you can
> suggest a better comment for the config file that wouldn't hurt, but
> it's a very minor option.

--
Randy Primeaux
randy@cloudfactory.org
tranze@hyperreal.org






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