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	Sat, 11 Apr 1998 16:14:15 +1000
Date: Sat, 11 Apr 1998 16:14:15 +1000
From: Bruce Evans <bde@zeta.org.au>
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To: bde@zeta.org.au, sos@FreeBSD.ORG
Subject: Re: cvs commit: src/sys/i386/isa wd.c
Cc: cvs-all@FreeBSD.ORG, cvs-committers@FreeBSD.ORG, cvs-sys@FreeBSD.ORG
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>> The Quantum Bigfoot 12G can probably be supported without using
>> LBA mode.  Since the old driver sort of worked, this drive must
>> support CHS mode, so it should all be accessible using any CHS
>> translation with 65535 * heads * sectors >= wp->wdp_lbasize.
>> Just set its size to wp->wdp_lbasize instead of to the default,
>> and adjust the number of cylinders.  (diskslice_machdep.c already
>> does similar adjustments if any slice seems to go beyond the
>> end of the disk, but it is too CHS-centric and only works up to
>> C=1024).
>
>This might be possible, but according to the ATA4 std. the CHS
>mode is "optional" for the drive makers, so we cannot knwo.

We can know - see my next paragraph.

>Its also easier to just use LBA all over :)

It's harder, because very old drives don't support it, and it is
not easy to tell which old drives support it.

>> The need for LBA can probably be determined automatically using
>> (wp->wdp_heads == 0 && wp->wdp_sectors == 0).  (ATA-4 permits
>> drives larger than 8G to not support CHS.  If it is not supported,
>> then the default translation is 0/0.)  I think we won't see any
>> drives that don't support it until 8G is a tiny drive.
>
>Right, but this only works if the drives implements the optional
>part above. I dont knwo before I get HW to test on.

Testing proves nothing, since future drives are not required
to support it.  OTOH, current models of the Quantum Bigfoot 12G
obviously support it, since otherwise the bug reports would be
about division by 0 instead of missing sectors.

Bruce

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