1 Feb
2014
1 Feb
'14
8:49 a.m.
So, I've got a PC here with a brain-dead BIOS that only acknowledges 3.5"
HD drives. Ugh. I can hook up a 5.25" HD drive instead and override the
BIOS type when booting Linux (passing "floppy=0,2,cmos" to the kernel), and
that seems to work.
However, when hooking up a (good) 5.25" DD drive (and using
"floppy=0,1,cmos") I consistently get I/O errors.
Anyone have any theories as to what the problem might be? Maybe the FDC in
the machine just plain doesn't support 250k/s transfer rates (unfortunately
I don't have any 3.5" DD media to test that by formatting a disk in a 3.5"
HD drive) - but that would seem like a weird feature to abandon?
Formatting 5.25" DD media in the HD drive *appears* to work, but I assume
that will be using a 300k/s rate rather than 250 (and of course the
narrower head width makes it pointless anyway)
I can haul another PC out of storage with a better BIOS/FDC, but I'm still
curious as to what the problem might be with this setup. Linux just
identifies the FDC as a "post-1991 82077" (for which 250k support is
claimed), but I expect it's a reimplementation within a larger I/O chip
rather than a discrete FDC IC.
cheers
Jules
1 Feb
1 Feb
11:19 a.m.
On 02/01/2014 08:49 AM, Jules Richardson wrote:
Anyone have any theories as to what the problem might
be? Maybe the FDC
in the machine just plain doesn't support 250k/s transfer rates
(unfortunately I don't have any 3.5" DD media to test that by formatting
a disk in a 3.5" HD drive) - but that would seem like a weird feature to
abandon?
Do you own a piece of opaque tape? Tape over 3.5" the media indicator
hole and you have a DSDD floppy that's good enough for testing.
If that works to create a "720K" floppy then you can try setting your
5.25' HD drive to operate in dual-speed mode (i.e. 360 RPM at high
density and 300 RPM at low density). Recall that density switching on a
5.25" HD drive also requires that a signal on pin 2 of the drive
connector be present, so be prepared to furnish one if it's not present
on the interface.
--Chuck
12:30 p.m.
On 02/01/2014 01:19 PM, Chuck Guzis wrote:
On 02/01/2014 08:49 AM, Jules Richardson wrote:
Yes, good point :)
Anyone have any theories as to what the problem
might be? Maybe the FDC
in the machine just plain doesn't support 250k/s transfer rates
(unfortunately I don't have any 3.5" DD media to test that by formatting
a disk in a 3.5" HD drive) - but that would seem like a weird feature to
abandon?
Do you own a piece of opaque tape? Tape over 3.5" the media indicator hole
and you have a DSDD floppy that's good enough for testing. If that works to create a "720K" floppy then
you can try setting your 5.25'
HD drive to operate in dual-speed mode (i.e. 360 RPM at high density and
300 RPM at low density).
Can do - is the aim then to set the drive (according to software) to be a
DD drive (which will then use a 250k rate), just to see if it works against
this particular FDC? Recall that I don't seem to have any particular
problems writing DD media in the HD drive as it stands - I just don't
expect it to necessarily be reliable when subsequently used in a machine
with a DD drive. It's just the use of a DD drive on the modern PC which is
causing trouble for some reason.
Recall that density switching on a 5.25" HD
drive
also requires that a signal on pin 2 of the drive connector be present, so
be prepared to furnish one if it's not present on the interface.
Yes, not sure in this case - although I can see where pin 2 of the
connector hooks up to an IC on the HD drive, so I can see if it's doing
anything easily enough.
cheers
Jules
2:11 p.m.
Jules Richardson <jules.richardson99 at gmail.com> writes:
However, when hooking up a (good) 5.25" DD drive
(and using
"floppy=0,1,cmos") I consistently get I/O errors.
Are the jumpers on the drive set correctly for a PC? I had the same
problem when I was using a drive that came from a BBC Micro last year --
the PC was expecting the disk change signal to be inverted from the BBC,
so Linux wouldn't do anything with the drive until I'd fitted the
appropriate jumper:
http://offog.org/notes/archiving/minifloppies/
Dave Dunfield's ImageDisk boot disk includes the TESTFDC tool that'll
tell you what encodings your controller supports, which might be worth a
try:
http://www.classiccmp.org/dunfield/img/index.htm
Linux just identifies the FDC as a "post-1991
82077" (for which 250k
support is claimed), but I expect it's a reimplementation within a
larger I/O chip rather than a discrete FDC IC.
"lspci" should give you a better idea of what the chipset actually is. I
was able to find the datasheet for mine...
Thanks,
--
Adam Sampson <ats at offog.org> <http://offog.org/>
3748
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