Haig or JB: an IRQ question

[Holerith]

I've noticed in a number of posts people using G400's with IRQ's below 9 and wondered if the G400 was free of the problems the G200 had on edge triggered vs level triggered events?


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Dean
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PDP-11, Dec-writer & ZD-11 Terminal Unit, RSTS-OS

[Zwisch]

Hi,
Some users are happy and not suffering from any problems with their G400 on IRQ 5... but other are having problems and it is always hard to see if this couldn't be the IRQ's fault... If you have the option and feel like playing around with those IRQ's I would definately do so to bring it to something a bit higher... but if it works for you on 5, then why fix something that isn't broken

[JAZZ]

Hi,

5 is not the best of options but one of my coworkers has a G400 in his system and from what he's telling me it's on 5 with no problems. Then again he does emails most of the day so hard to see if a problem would arise...

Ciao
J

[Zwisch]

The problem with 5 is not only of the edge triggering but also that this is one of the IRQ's with the least priority over the BUS... hence if you have several device in your system with no free IRQ's, then having the card on 5 might be slighly problematic..

[J.B. Matrox Tech]

The reason that IRQ 5 is not a recommended IRQ for the video card is because of how low on the chain of IRQs that 5 is. If you know about how IRQ's work the order is 0,1,2,9,10,11,12,13,14,15,3,4,5,6,7,8 the reason for this is that IRQs are created using 2 IRQ chips (the 8259 Controller) IRQs used to be only up to 8 with previous systems (8086 and 8088) to allow for greater expendability, we had to incorporate another Controller chip (the second 8259 chip) Thus we use the first controller for 0 and 1 (System Timer and Keyboard) then Cascade IRQ 2 to 9 so if you check what is on IRQ 2 it states "Programmable Interrupt Controller" thus the new order of non linear IRQs begins (0,1,2,9,10,11,12,13,14,15,3,4,5,6,7,8). So when you ask about IRQ 5 for video it is considered to low. If your video card is on 5 and all is fine the old rule applies "If it ain't broke don't fix it", but if errors begin then a recommend location for a video card is any IRQ from 9-12. Of course sharing is not recommended other than being with an IRQ holder for PCI steering (each major device requires it to properly utilize the IRQ).

[Nuno]

Impressive...