AGP adapter do not accepts IRQ

Recommended by Wim's BIOS...

Gentlemen:
I have an old M748LMR board in which I've tried several AMI BIOS versions with the same problem: Is impossible to assign an IRQ to the on-board SiS620 AGP adapter. I have some experience flashing BIOS and searching right drivers, but I´m quite obsessioned to knows the reason of this problem...
Any suggestions?
Cordial greetings from the Patagonia, Argentina.

[Denniss]

AFAIK this VGA does not need an IRQ

VGA drivers :
http://driver3.sis.com/graphic/integrated/620/
Chipset drivers :
http://driver3.sis.com/agp/

Thanks Dennis for your response.
As far as I know, any kind of AGP, specially olders, works a bit more faster with an IRQ.
Sandra diagnostic tool suggests same fix, but configuring it from BIOS options, then no IRQ is assigned to SiS 620 AGP adapter.
Do you think that I should not give importance to this question?
Thanks again,
Horacio