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Date:      Thu, 2 Dec 1999 22:42:18 -0800 (PST)
From:      Matthew Jacob <mjacob@feral.com>
To:        Mike Smith <msmith@FreeBSD.ORG>
Cc:        Stephen McKay <syssgm@detir.qld.gov.au>, freebsd-scsi@FreeBSD.ORG
Subject:   Re: Tape driver problems 
Message-ID:  <Pine.BSF.4.10.9912022241090.23244-100000@beppo.feral.com>
In-Reply-To: <199912030632.WAA05573@mass.cdrom.com>

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> > 
> > See other mail. I still believe that the AHA driver should work better,
> > but it's a low priority item now.
> 
> This particular issue is a defect in the bounce-buffering code; the 1542 
> is limited to 16 or maybe 17 s/g entries.  (We allow 17, the Linux driver 
> stops at 16.)  This isn't an issue for most things until you get up near 
> 64k, where fragmentation lets you run out of page-sized entries.  I'm not 
> sure how best we could work around this without clustering pages in 
> bounce-buffer memory.  If you've got any neat ideas I'll happily file 
> them for next time someone goes looking at that code.

I've hacked on the AHA1542X substantially, but it's been years. It
actually had a reasonable target mode. I just don't have time and if I
solve the current problem a different way, we don't have to worry about it
at the moment.

-matt




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