P4 APM functionality

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I am using a P4 box running VxWorks RTOS for a simulation application.
The simulations went out of sync when the APM (power mgmt) bios
settings kicked in after 15 minutes and turned off the screen display.
I disabled the APM and all is fine now. But I was wondering, how does
really the APM setting in BIOS works? Are there timers that trigger an
harware CPU interrupt and CPU branches to some APM code on BIOS chip?
how does it work? I am curious to know.

Thanks in advance.


Re: P4 APM functionality

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By AMD's documentation, System Management Mode is entered after receiving
external nonmaskable signal (eg, a timer).
By default, it is handled by BIOS. You can reprogram some MSRs to change the
address of the SMM routine and/or rewrite it by a new code.

- page 365 and so...

Have a nice day
Zdenek Sojka

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