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IRQ Wake-Up Events and Activity Monitors

When the system enters a power-down mode, it will look for activity to tell it when to wake back up. Normally you wake the system back up either by pressing a key or moving the mouse. However, you may want the system to wake up in response to other events. For example, you might want the system to wake up when activity on the modem is detected, if your PC answers incoming faxes. Some BIOSes give you the ability to specify whether or not activity on an IRQ will wake up the system.

The BIOS monitors the system for "activity" to determine when to enable power management. You can tell the system what it should consider activity and what it should not, in other words, what sorts of events on the PC should reset the idle counter for power management. For example, in almost every case a movement of the mouse or a keypress could be considered activity. However, if you have a sensitive mouse that can move slightly in response to vibration, you might want to set the BIOS so that movement on the mouse will not reset the power management countdown timers.

There will normally be a separate setting for each IRQ. For each one, the options will typically be:

• Wake Up: Activity on this IRQ will wake up the system when in a power-down mode.
• Monitor: Activity on this IRQ will reset the system idle countdown timers.
• Both: Activity on this IRQ will both wake up the system when powered down and reset the idle timers when powered up.
• Neither: Activity on this IRQ will neither wake the system nor reset idle timers.

The default for these depends on the system. Some BIOSes use similar controls with different names, or may separate the wake up event controls from the monitoring controls. If you are using power management you will want to tailor these based on what interrupts (devices) are in use on your system. Look here for information on what the typical IRQ allocations are on a PC.

Tip: For a system with a PS/2 style mouse, the mouse will be on IRQ 12. For a system with a serial mouse, the mouse will be on whatever IRQ is assigned to the COM port the modem is using. This is usually COM1, which uses IRQ 4.

Note: IRQ1, which is generated by the keyboard, is not usually listed here as it always causes a wake-up from power management, and cannot normally be disabled.

Next: Integrated Peripherals

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