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Re: ACPI, APIC



Tom Browder wrote:
> Can someone explain or point to more info on ACPI and APIC what it means
> when booting to see something like "ACPI and S3 don't like each other..."?

To enhance on Tammo's answer...

ACPI, Advanced Configuration and Power Interface, is a standardised set
of interfaces for letting the operating system know what hardware is
there and how to set it up. It also tells the OS how to put it into a
low power (or no power) mode when the OS is being suspended (to RAM or
disk, for example).

An interrupt is a way for the processor and the hardware to let each
other know that there's data waiting to be serviced. So, for example,
when an Ethernet card detected that it had received data intended for
that PC, it would send an interrupt. The interrupt would (normally)
trigger the processor to stop running the current program, and switch
control to the operating system. The OS would work out that the Ethernet
device had sent the interrupt, arrange for the incoming data to be
copied somewhere safe, and return control to the program. (Later, the OS
would decode the data it had been sent).

A PIC, a Programmable Interrupt Controller, is something that receives
interrupts from a number of devices, sends an interrupt to the
processor, and then can be queried by the processor to find out which
device sent the interrupt in the first place. (That simplifies the
processor interface, you see.)

The original IBM PC and its immediate successor, the PC XT defined a
rather simple PIC scheme with a number of limitations. So an Advanced
Programmable Interrupt Controller was defined, that can cope with more
devices and share them evenly among multiple processors.

The message I think you were asking about is "ACPI: S3 and PAE do not
like each other for now, S3 disabled." S3 is an ACPI "sleep state",
"Suspend to RAM". PAE is Intel's Physical Address Extensions, a way of
getting a 32 bit computer to use more than 4 GB of RAM. Fedora kernels
are compiled to use PAE, and this evidently interfered with suspending
to RAM.

The limitation appears to have been in the Linux code, since this
message doesn't appear in 2.6.9 source (although I'm looking at the
kernel.org source here, not the Fedora tree). So if you aren't on the
latest kernel, update it and you should see the message go away.

Hope this helps,

James.
-- 
E-mail address: james | "Luck is my middle name," said Rincewind,
@westexe.demon.co.uk  | indistinctly. "Mind you, my first name is Bad."
                      |     -- Terry Pratchett, Interesting Times


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