How XP assigns IRQ?

[Guest]

Hello,

I would like to know how XP assigns IRQ for each devices that are on the
ACPI enabled system.

Let me explain my problem, I have a system where IRQ 7 & 11 are
free/available. When I plug 2 16-bit PCMCIA cards in its slots, OS finds it
and assigns 11 for one card and either irq 3 or 4 for another card that
conflicts with COM ports. why OS assigns irq 3/4 even though IRQ 7 is
available.

I could get rid of this conflicts if I do the following steps,
1. Assign IRQ 7 for COM port and boot the system. Insert one PCMCIA card.
2. Assign IRQ 4 back to COM port and boot the system. Insert the second
card.

Now XP assigns IRQ 7 for the second one and no conflicts. Why its so? Is
it a BIOS issue or OS issue? Any soln?

I tried with different types of 16-bit PCMCIA card from different vendors.
Still the same problem. When I tried to reinstall the OS with two PCMCIA
card inserted, I get blue screen.

Thanks in advance.

 

[Carey Frisch [MVP]]

A general description of IRQ sharing in Windows XP
http://support.microsoft.com/kb/314068/EN-US/

--
Carey Frisch
Microsoft MVP
Windows XP - Shell/User

Be Smart! Protect Your PC!
http://www.microsoft.com/athome/security/protect/default.aspx

------------------------------------------------------------------------------

:

| Hello,
|
| I would like to know how XP assigns IRQ for each devices that are on the
| ACPI enabled system.
|
| Let me explain my problem, I have a system where IRQ 7 & 11 are
| free/available. When I plug 2 16-bit PCMCIA cards in its slots, OS finds it
| and assigns 11 for one card and either irq 3 or 4 for another card that
| conflicts with COM ports. why OS assigns irq 3/4 even though IRQ 7 is
| available.
|
| I could get rid of this conflicts if I do the following steps,
| 1. Assign IRQ 7 for COM port and boot the system. Insert one PCMCIA card.
| 2. Assign IRQ 4 back to COM port and boot the system. Insert the second
| card.
|
| Now XP assigns IRQ 7 for the second one and no conflicts. Why its so? Is
| it a BIOS issue or OS issue? Any soln?
|
| I tried with different types of 16-bit PCMCIA card from different vendors.
| Still the same problem. When I tried to reinstall the OS with two PCMCIA
| card inserted, I get blue screen.
|
| Thanks in advance.