[PlanetCCRMA] pci latency_timer , usb soundcard

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Mon Jan 21 12:33:01 2008

On Mon, 2008-01-21 at 21:00 +0100, Florent Berthaut wrote:
> i have a problem with my new laptop and fedora 8 ccrma.
> I have a lot of xruns when trying to use my m-audio fast track pro (usb) 
> , so i decided to try to change the latency timer (which worked well 
> with my previous laptop) for the usb controller.
> But when i do :
> /sbin/setpci -v -s 00:1d latency_timer=ff
> and then : /sbin/lspci -v, the latency timer still shows 0 :
> 00:1d.7 USB Controller: Intel Corporation 82801H (ICH8 Family) USB2 EHCI 
> Controller #1 (rev 03) (prog-if 20 [EHCI])
>         Subsystem: Samsung Electronics Co Ltd Unknown device c510
>         Flags: bus master, medium devsel, latency 0, IRQ 20
> So how can i change it ?

I don't know why but on some hardware it is not possible to change the
latency timer. So if the laptop is different that might be the case. 

> I tryed dmesg and at some point it says:
> ACPI: PCI Interrupt 0000:00:1d.0[A] -> GSI 23 (level, low) -> IRQ 20
> PCI: Setting latency timer of device 0000:00:1d.0 to 64
> uhci_hcd 0000:00:1d.0: UHCI Host Controller
> uhci_hcd 0000:00:1d.0: new USB bus registered, assigned bus number 5
> uhci_hcd 0000:00:1d.0: irq 20, io base 0x00001840
> So the latency timer seems to be set to 64 .
> Can i change the startup script which set this ?

I don't think the startup scripts have anything to do with the latency
timer. That's probably the kernel itself setting it (at least that's my
guess). "64" is a reasonable value, actually. 

Did you try setting a less extreme value other than "ff"?

I also have an "older" kernel that seems to work better on some hardware
for f8, it is based on

-- Fernando