Re: IO delay, port 0x80, and BIOS POST codes

H. Peter Anvin (hpa@zytor.com)
14 Mar 2002 13:56:20 -0800

Followup to: <Pine.LNX.3.95.1020314164142.382B-100000@chaos.analogic.com>
By author: "Richard B. Johnson" <root@chaos.analogic.com>
In newsgroup: linux.dev.kernel
>
> Well no, IO doesn't "time-out". The PC/AT/ISA bus is asychronous, it's
> not clocked. If there's no hardware activity as a result of the write
> to nowhere, it's just a no-op. The CPU isn't slowed down at all. It's
> just some bits that got flung out on the bus with no feed-back at all.
>

An OUT on the x86 architecture is synchronous... the CPU will not
proceed until the OUT is present on the bus. This is a requirement of
the SMM architecture, actually.

-hpa

-- 
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
"Unix gives you enough rope to shoot yourself in the foot."
http://www.zytor.com/~hpa/puzzle.txt	<amsp@zytor.com>
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