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SubjectRe: Direct access to hardware
On Tue, 25 Jul 2000, Stuart MacDonald wrote:

> From: "James Sutherland" <jas88@cam.ac.uk>
> > As with some of the Intel CPU bugs, the problem is NOT "invalid ATA
> > commands" - it's a matter of VALID commands which are dangerous. FDIV on
> > early Pentiums isn't an invalid instruction - it just produces the wrong
> > results at times. So the SOFTWARE must do something to avoid this - either
> > that, or you need to replace the hardware, which isn't desirable. You do
> > something in the OS to prevent these problem commands being used.
>
> You agree it's a hardware bug. Which implies it should be fixed. In
> hardware. Not worked around in software. Sometimes, as with the
> pentium bug, you do want to hack things, since doing so works
> around the problem and Intel wasn't forth coming with a hardware
> fix at first. No functionality was lost with the work around. Not so here.
> Functionality will be lost.

What functionality? Remember, only the commands which should NEVER be
issued except as part of a low-level diagnostic or maintenance procedure.
Since nothing should ever issue these commands anyway except the vendor's
own software, no functionality is being lost by disabling them, except for
that software, which can be adapted to work around that problem in a way
which will also improve it significantly.


James.


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