APM vs ACPI

[Brett I. Holcomb]

Thank you!  So I should choose ACPI when I build a kernel since my board 
supports it and disable APM.

> On Fri, 2002-12-20 at 23:14, Brett I. Holcomb wrote:
>> What is the difference in APM vs ACPI for power management?  Are they two
>> exclusive methods of controling shutdown, etc. or is ACPI an advanced
>> version of APM?  When I build a kernel can I specify both or do I choose
>> one?
> 
> 
> Well, here is the difference between the two (At least as I understand
> it):
> 
> APM is a a BIOS-based scheme of system power management. It provides CPU
> and device power management and uses device activity timeouts to
> determine when to transition devices to low power states.
> 
> However, APM falls short:
> 
> 1.) Every BIOS has its own power management scheme. There is no
> consistancy between manufacturers. Each BIOS developer must refine and
> maintain their own APM BIOS code and functionality.
> 
> 
> 2.) The reason for a suspend is never known.
> 
> 
> 3.) The BIOS is unaware what the user is doing. Ultimately, the BIOS
> makes a mess of everything.
> 
> 4.) The BIOS knows nothing about USB devices, add-in cards and IEEE 1394
> devices.
> 
> 
> ACPI was developed to overcome the deficiencies in APM. ACPI (Advanced
> Configuration and Power Interface) is an open industry specification.
> 
> ACPI evolves the existing collection of power management BIOS code,
> Advanced Power Management (APM) application programming interfaces
> (APIs, PNPBIOS APIs, Multiprocessor Specification (MPS) tables and so on
> into a well-defined power management and configuration interface
> specification. The specification enables new power management technology
> to evolve independently in operating systems and hardware while ensuring
> that they continue to work together.
> 
> Unlike APM, ACPI allows the Operating System (instead of the BIOS) to
> control Power Management (OSPM). The support code provided by the BIOS
> is not written in the native assembly language of the platform but in
> AML (ACPI Machine Language). The BIOS does not determine the policies or
> time-outs for power management or resource management.
> 
> 
> There are 4 device states under APM: Enabled, Standby, Suspend and Off.
> 
> ACPI's device states are extended, with 4 major global states: Working
> (S0), Sleeping (S1-S3), Soft-Off (S4), and Mechanical-Off (S5). Sleeping
> is further broken down into 3 substates.The ACPI BIOS tables define what
> these states mean for individual devices, and the operating system
> determines when to move a device, or even the entire system, from one
> state to another.
> 
> The ACPI-compatible OS mainly acts as a swap manager that swap the
> computer to different state based on the information collected. A
> transition from one state to another is first started with the OSPM
> system code which instructs the OS kernel for the specific state
> transition. After the kernel receives the instruction, it asks the
> appropriate device driver to perform the operation. Response from the
> operation will be passed back to the OSPM from the kernel. This process
> will proceed in hierarchical order until all devices and components
> reach a specified state.
> 
> There is more, but the above info is probably enough...............
> 
> 
> 
> Best
> 
> Peck

-- 
Brett I. Holcomb
brettholcomb at R777charter.net
AKA Grunt <><
Registered Linux User #188143
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