Hi,
Anybody knows how Windows NT HAL maps the hardware IRQs to its
internal DIRQLs? Is is possible to reserve a high DIRQL (eg DIRQL27)
for certain hardware? I need the highest DIRQL to run my device since
it’s used for a very time-critical purpose.
Thanks.
Ma Jun
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You do not have control over how the system maps IRQ’s to DIQRLs.
Paul Lever
----- Original Message -----
From: “Ma Jun”
To: “NT Developers Interest List”
Sent: Wednesday, April 04, 2001 11:57 PM
Subject: [ntdev] IRQ to DIRQL mapping
> Hi,
>
> Anybody knows how Windows NT HAL maps the hardware IRQs to its
> internal DIRQLs? Is is possible to reserve a high DIRQL (eg DIRQL27)
> for certain hardware? I need the highest DIRQL to run my device since
> it’s used for a very time-critical purpose.
>
> Thanks.
>
> Ma Jun
>
>
> —
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Ma Jun:
If you have a time critical application, you may find an answer by
subscribing and
posting that question to the ntrealtime mailing list.
There is a product by BSquare that may already solve your problem. Check
their web.
George
At 02:57 PM 4/5/01 +0800, you wrote:
Hi,
Anybody knows how Windows NT HAL maps the hardware IRQs to its
internal DIRQLs? Is is possible to reserve a high DIRQL (eg DIRQL27)
for certain hardware? I need the highest DIRQL to run my device since
it’s used for a very time-critical purpose.Thanks.
Ma Jun
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> Anybody knows how Windows NT HAL maps the hardware IRQs to its
internal DIRQLs?
You shouldn’t depend on this, but for a non-APIC x86 PC system under NT
4.0:
IRQL + IRQ# = 27
Thus, if your IRQL is 16, then you’re servicing IRQ 11.
Is is possible to reserve a high DIRQL (eg DIRQL27) for certain hardware?
For IRQ 0, the answer is no, unless you’re the clock interrupt. 
Generally, you might be able to do what you want with the BIOS settings
and/or Plug and Play.
Note that there’s some weirdness that goes on because NT prioritizes the
IRQs from 15 (lowest) -> 0 (highest). However, the non-APIC hardware
prioritizes them from 7 (lowest) -> 3, 15 -> 8, 2 -> 0 (highest). NT tries
to work around that, but fails under some cases. There was a good
discussion of this in a Dr. Dobb’s Journal article about 4 or more years
ago, but frankly, I forget the author (even though we exchanged a whole
bunch of email) and any details.
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Taed,
Thanks a lot for your information.
> Anybody knows how Windows NT HAL maps the hardware IRQs to its
> internal DIRQLs?
You shouldn’t depend on this, but for a non-APIC x86 PC system under NT
4.0:
IRQL + IRQ# = 27
Thus, if your IRQL is 16, then you’re servicing IRQ 11.
I check on my machine, it’s a CompactPCI system with one AMD CPU and NT 4.0,
it’s exactly like what you said: IRQL + IRQ# = 27.
That means the highest IRQL I can use is IRQL24, which is IRQ3 phsically,
used
by COM2 normally, am I right?
> Is is possible to reserve a high DIRQL (eg DIRQL27) for certain
hardware?For IRQ 0, the answer is no, unless you’re the clock interrupt.
Generally, you might be able to do what you want with the BIOS settings
and/or Plug and Play.Note that there’s some weirdness that goes on because NT prioritizes the
IRQs from 15 (lowest) -> 0 (highest). However, the non-APIC hardware
prioritizes them from 7 (lowest) -> 3, 15 -> 8, 2 -> 0 (highest). NT
tries
to work around that, but fails under some cases. There was a good
discussion of this in a Dr. Dobb’s Journal article about 4 or more years
ago, but frankly, I forget the author (even though we exchanged a whole
bunch of email) and any details.
For today’s normal one-cpu system, does it still use PIC to deal with
interrupt or
already update to APIC? How do I check?
If I use a non-APIC system, that means the hardware priorities are from
(lowest)7->3, 15->8, 2->0(highest), for IRQ3, it still has phsically lower
priority
than IRQ9, so even I choose IRQ3 (which can get IRQL24 inside NT), it
can preempted by IRQ9 phsically, no matter how NT deals with it, if so, I
still
can not guarantee that IRQ3 (DIRQL24) always has the higher priority than
other
devices. Is it true?
Unfortuntely I can not find the discussion you’ve metioned.
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