Messages in this thread | | | From | "H. Peter Anvin" <> | Subject | Re: IO delay, port 0x80, and BIOS POST codes | Date | 14 Mar 2002 13:56:20 -0800 |
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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.
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