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Date: Wed, 10 Feb 2016 20:33:14 +0300
From: Roman Kagan <rkagan@virtuozzo.com>
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Subject: Re: [Qemu-devel] [PULL 48/49] i386: populate floppy drive
 information in DSDT
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To: John Snow <jsnow@redhat.com>
Cc: Peter Maydell <peter.maydell@linaro.org>, Eduardo Habkost <ehabkost@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Laszlo Ersek <lersek@redhat.com>, Richard Henderson <rth@twiddle.net>

On Wed, Feb 10, 2016 at 12:16:32PM -0500, John Snow wrote:
> On 02/10/2016 12:10 PM, Roman Kagan wrote:
> > Well, as I wrote in another mail, SeaBIOS, which is supposed to provide
> > the same information to int 0x13/0x08, populates it with static data
> > based only on the drive type as encoded in CMOS at initialization time,
> > and everyone seem to have been fine with that so far.  I'll need to
> > re-test it with real Windows guests, though.
> > 
> 
> OK, but what we appear to be doing currently is polling the current
> geometry values for a drive instead of some pre-chosen ones based on the
> drive type.
> 
> What values does SeaBIOS use? (Can you point me to the table it uses?)

src/hw/floppy.c:

struct floppyinfo_s FloppyInfo[] VARFSEG = {
    // Unknown
    { {0, 0, 0}, 0x00, 0x00},
    // 1 - 360KB, 5.25" - 2 heads, 40 tracks, 9 sectors
    { {2, 40, 9}, FLOPPY_SIZE_525, FLOPPY_RATE_300K},
    // 2 - 1.2MB, 5.25" - 2 heads, 80 tracks, 15 sectors
    { {2, 80, 15}, FLOPPY_SIZE_525, FLOPPY_RATE_500K},
    // 3 - 720KB, 3.5"  - 2 heads, 80 tracks, 9 sectors
    { {2, 80, 9}, FLOPPY_SIZE_350, FLOPPY_RATE_250K},
    // 4 - 1.44MB, 3.5" - 2 heads, 80 tracks, 18 sectors
    { {2, 80, 18}, FLOPPY_SIZE_350, FLOPPY_RATE_500K},
    // 5 - 2.88MB, 3.5" - 2 heads, 80 tracks, 36 sectors
    { {2, 80, 36}, FLOPPY_SIZE_350, FLOPPY_RATE_1M},
    // 6 - 160k, 5.25"  - 1 heads, 40 tracks, 8 sectors
    { {1, 40, 8}, FLOPPY_SIZE_525, FLOPPY_RATE_250K},
    // 7 - 180k, 5.25"  - 1 heads, 40 tracks, 9 sectors
    { {1, 40, 9}, FLOPPY_SIZE_525, FLOPPY_RATE_300K},
    // 8 - 320k, 5.25"  - 2 heads, 40 tracks, 8 sectors
    { {2, 40, 8}, FLOPPY_SIZE_525, FLOPPY_RATE_250K},
};

The array is indexed by the floppy drive type from CMOS

Roman.