[linux-audio-user] IRQ settings and low latency

cv223 at comcast.net cv223 at comcast.net
Fri Mar 12 12:42:01 EST 2004


I have the exact same problem and the exact same questions. I haven't seen any responses to Greg's email, so I thought I would reiterate the question.  Anyone have any insight?

Thanks,

Joel
> Hi,
> 
> I've been working on getting my linux system set up for recording with
> jack/ardour.  I came across the "Low Latency mini howto":
> http://www.djcj.org/LAU/guide/Low_latency-Mini-HOWTO.php3
> 
> At the end, it talks about setting up IRQs such that the sound card is
> at a high priority relative to other devices in the system.  However,
> all the information in the doc pertains to non-APIC machines.  What
> about an APIC-enabled machine?
> 
> The output of 'cat /proc/interrupts' shows my sound card (ICE1712) dead
> last:
> 
>            CPU0       CPU1       
>   0:    6628091          0    IO-APIC-edge  timer
>   1:          6          0    IO-APIC-edge  keyboard
>   2:          0          0          XT-PIC  cascade
>   9:          0          0          XT-PIC  acpi
>  12:        803          0    IO-APIC-edge  PS/2 Mouse
>  15:          5          0    IO-APIC-edge  ide1
>  16:          0          0   IO-APIC-level  usb-uhci, usb-uhci
>  18:       4178          0   IO-APIC-level  libata, usb-uhci
>  19:        320          0   IO-APIC-level  usb-uhci
>  20:       6406          0   IO-APIC-level  eth0
>  21:          0          0   IO-APIC-level  ICE1712
> NMI:          0          0 
> LOC:    6628191    6628246 
> ERR:          0
> MIS:          0
> 
> output of: lspci -v -s 02:01.0   
> 02:01.0 Multimedia audio controller: IC Ensemble Inc ICE1712 [Envy24]
> (rev 02)
>         Subsystem: IC Ensemble Inc: Unknown device d634
>         Flags: bus master, medium devsel, latency 32, IRQ 21
>         I/O ports at 8000 [size=32]
>         I/O ports at 8400 [size=16]
>         I/O ports at 8800 [size=16]
>         I/O ports at 8c00 [size=64]
>         Capabilities: [80] Power Management version 1
> 
> I've tried manually setting IRQs in the BIOS, moving the card around,
> etc.  No amount of tweaking can move it any higher in the list. (It's
> set to IRQ 10 in the BIOS)
> 
> I guess my question is: Does the IRQ priority matter when IRQs are
> abstracted by the APIC?  If so, how does one change the priority in this
> situation?  I'm running 2.4.22, with the low latency and kernel
> preemption patches installed.
> 
> Thanks,
> Greg
> 
> -- 
> Greg Jednaszewski
> greg at attenuated.org



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