Subject: Re: Floppy won't boot with internal cache enabled

From: [email-masked] (Bruce Perens)
Date: Thu, 8 Aug 96 17:02 PDT

On Tue, 6 Aug 1996, Steve Gaarder wrote: 
> I am installing Debian 1.1.1 on a generic clone with an AMD 486 on an
> Opti-based motherboard.  If I have the internal cache enabled in setup,
> I get the error "invalid compressed format" after the "uncompressing
> Linux" message.  If I disable the cache, it boots fine.  It boots ok
> from the hard drive either way.  Anyone know what is going on?

This message indicates that incorrect data was read from the floppy.
Since disabling the cache fixes it, you have verified that the floppy
itself contains valid data and the problem comes after that.

Guy Maor: 
> Try to enable it but make the timings more conservative.
> You're probably seeing hardware problems; your L2 cache is being
> addressed too quickly.

Good idea. Try it. I have another suggestion if that does not work. If
I am not mistaken, loading the root disk is the first place where the
Linux floppy driver is used. The boot disk is read using BIOS. Try to
exercise the floppy from Linux with your cache enabled by writing a
large file to it, popping out and re-inserting the floppy, and reading
back the file. Use "md5sum" to see if the data matches. Don't forget
to pop out and replace the floppy - the data could be read from a disk
block cache rather than the floppy if you don't do that. This block cache
has nothing to do with the cache you are enabling and disabling. If
there's a problem, I would suspect the Linux floppy driver (which
sometimes needs to be tuned for various systems), but it could be
something that is solved by changing a DMA speed setting in your BIOS
set-up menu as well.

	Thanks

	Bruce

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From: Guy Maor <[email-masked]>
Date: Thu, 8 Aug 1996 15:23:01 -0500 (CDT)

On Thu, 8 Aug 1996 [email-masked] wrote:

> > ... Don't forget
> >block cache rather than the floppy if you don't do that. ...
> 
> Does this note mean that one can replace floppy disks without unmounting
> and mounting in between?  Or were the 'umount' and 'mount' implied by
> "pop out"?  If they were, wouldn't the 'umount' and 'mount' alone be 
> sufficient without physically removing the disk?

There are other ways to get data from a floppy besides mounting and
unmounting, mtools or just raw data (ie - dd).  Those could be fooled
but shouldn't be on most floppy drive.  Use fdflush if you're nervous.

Guy

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From: [email-masked]
Date: Thu, 8 Aug 1996 15:54:53 -0400

Just Curious