K7VAT
System Board 26
USB and PCI slot 1 and PCI slot 3 use the same interrupt, and AGP, PCI slot 5 use the same
interrupt. Because PCI interrupts are shareable this is OK. The BIOS contains the following
items related to PCI interrupts:
BIOS item
Settings
Explanation
Assign IRQ to
USB
Enabled/disabled If the USB ports are not used, the user can set this item
to disabled. This will make sure that PCI INT D is only
granted to PCI slot 1, PCI slot 3.
Assign IRQ to
VGA
Enabled/disabled Most modern VGA cards require an interrupt to function.
If yours does not, disable this item to free the PCI
interrupt.
ACPI Interrupt
The ACPI specification defines that devices that support ACPI (Advanced Configuration
and Power Interface) can issue interrupts to the OS to notify it of an ACPI event. This
interrupt is called the SCI (System Control Interrupt), and it is always mapped to IRQ 9. If
ACPI is enabled (see the FAQ chapter, ACPI section), PCI devices will be able to make use
of IRQ 9, because PCI interrupts are shareable. But ISA PnP cards can not use IRQ9 if
ACPI is enabled.
Therefore the BIOS contains an item that allows the user to disable ACPI. This will release
IRQ 9 to the PnP interrupt pool for use by ISA PnP cards.
Assignment Sequence
The interrupts are assigned to the devices in the following sequence:
1.
The fixed interrupts are hardwired and are left out of the assignment process (IRQs
0,1,2,6,8 and 13)
2.
The BIOS determines what legacy ISA devices have been disabled in the BIOS setup
and releases these IRQs into the PnP interrupt pool
3.
The PnP interrupt pool now contains the free interrupts that can be assigned to PnP
devices.
There are 2 possible ways of assignment now, depending on the setting in the BIOS for the
PnP OS installed item. (On the PnP/PCI Configuration Setup page). If set to no, the A
sequence applies, if set to yes the B sequence.
A
PnP OS Installed: No
The BIOS will now assign all interrupts
1.
The BIOS first assigns the interrupts to the ISA PnP cards from the interrupt pool.
The interrupts (if available) are assigned in the following order: 15, 11, 10, 12, 14, 3,
4, 5, 7, 9. As mentioned, if ACPI if enabled, IRQ 9 will not be available.
