Re: Linux Post codes during runtime, possibly OT

Pavel Machek
2001-01-29T14:42:50Z

Hi!

> > > > It output garbage to the 80h port in order to enforce I/O delays.
> > > > It's one of the safe ports to issue outs to.
>
> > > Yes, because it is reserved for POST codes. You can get "POST
> > > debugging cards" that simply have a BIN -> 7segement encoder and two 7
> > > segment displays on them. They decode 0x80. That's what it's for.
>
> > Again, if you want to change it, find another safe port, test the hell
> > out of it, an *PUBLICIZE IT* so noone will use it in the future.
>
> I may have missed too much of the discussion, but I thought that the
> idea was that some people noted that their POST-code-cards don't
> really work all that well when Linux is running because Linux keeps on
> sending garbage to port 0x80.
>
> You seem to state that if you want POST codes, you should find a
> different port, modify the code, test the hell out of it, and then
> submit the patch.
>
> That is NOT the right way to go about this: Port 0x80 is RESERVED for
> POST usage, that's why it's always free. If people want to use it for
> the original purpose then that is a pretty damn good reason to bump
> the non-intended users of that port somewhere else.
>
> Now, we've found that small delays are reasonably well generated with
> an "outb" to 0x80. So, indeed changing that to something else is going
> to be tricky.
>
> All that I can think of right now is:
> - Find a register that can be written without side effects in
> "standard" hardware like a keyboard controller, or interrupt
> controller. Especially good are ones that already require us to keep
> a shadow value. Write the shadow variable to the register.
> (Tricky: not interrupt safe!)

What about just remembering shadow of 0x80 and always writing shadow
to 0x80? Interrupt unsafety hopefully does not matter much....
Pavel
--
I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care."
Panos Katsaloulis describing me w.r.t. patents at discuss@linmodems.org