Re: Linux Post codes during runtime, possibly OT

["mirabilos" <eccesys@topmail.de>]

----- Original Message ----- 
From: "Richard B. Johnson" <root@chaos.analogic.com>
To: "mirabilos" <eccesys@topmail.de>
Cc: "Linux-Kernel ML" <linux-kernel@vger.kernel.org>; "Mark H. Wood" <mwood@IUPUI.Edu>
Sent: Tuesday, January 30, 2001 6:36 PM
Subject: Re: Linux Post codes during runtime, possibly OT


> On Tue, 30 Jan 2001, mirabilos wrote:
> 
> > [...]
> > > > 
> > > > 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. 
> > > 
> > > So how bad would it be to give these people a place to leave the value
> > > that they want to have displayed, and have the delay code write *that*
> > > instead of garbage?
> > 
> > Because Port &h80 is _not_ decoded by the standard PC hardware.
> > There are some ISA and nowadays even PCI cards that convert the value
> > OUTted to that port into two 7-segment-digit-LCDisplays, buffered so
> > you can read it from the card, but normally no chipset actually
> > cares about that port. (I speak of Desktop PCs.)
> > 
> > I repeat: Any OUT to port &h80 is, as long as there are no special
> > extensions, just as well as any OUT to port &h1234 or &h4711 or
> > whateveryouwant as long as nothing uses it.
> > Since Port &h80 is now "reserved" for that POST code usage,
> > and it is the safest port one can use in order to delay,
> > Linux uses it.
> 
> This is not correct. Port 0x80 is not an "unused" port. It
> is decoded by standard hardware:
> 
> C:\>debug
> 
> -i 80
> AE
> -o 80 20
> -i 80
> 20
> -q
> \x1a
> 
> In this machine I do not have a 'POST-codes' board. Port 0x80 is
> an 8-bit read/write latch. It always has been.
> 
> 
> Cheers,
> Dick Johnson

OK, I'll check it against every box I've got here. I just was
citing what I've learned "ages" ago.


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