RE: Processor C states and USB problem

["Li, Shaohua" <shaohua.li-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

Hi,
C3 is a kind of idle, it means deep power saving.
Actually, I observed the same symptom as you: USB devices caused many bus master activities, which make processor can't enter C3.
 
Thanks,
Shaohua
> -----Original Message-----
> From: acpi-devel-admin-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org [mailto:acpi-devel-
> admin-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org] On Behalf Of mike@it-loops.com
> Sent: 2004年1月5日 16:42
> To: acpi-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
> Subject: [ACPI] Processor C states and USB problem
> 
> Recently I had problems with my network card and ACPI (see earlier posts
> for
> the problem and solution) so I thought I'd take a closer look at ACPI on
> this notebook (Acer Travelmate 800).
> 
> Looking at the proc entries for the processor I saw the following.
> 
> active state:            C3
> default state:           C1
> bus master activity:     80070020
> states:
>    C1:                  promotion[C2] demotion[--] latency[000]
> usage[00000010]
>    C2:                  promotion[C3] demotion[C1]
> latency[001]usage[01077887]
>   *C3:                  promotion[--] demotion[C2] latency[085]
> usage[00083507]
> 
> This looked pretty normal to me, apart from the fact that the processor
> was
> spending a lot of time in C3 although the notebook was idle.
> 
> Now I plugged in my USB mouse.
> 
> cat /proc/acpi/processor/CPU0/power
> active state:            C2
> default state:           C1
> bus master activity:     ffffffff <---- USB is active
> states:
>    C1:                  promotion[C2] demotion[--] latency[000]
> usage[00000010]
>   *C2:                  promotion[C3] demotion[C1]
> latency[001]usage[00871647]
>    C3:                  promotion[--] demotion[C2] latency[085]
> usage[00077386]
> 
> The processor never left the C2 state.
> After unplugging the mouse "bus master activity" showed normal values
> again.
> 
> Now for my two questions:
> 
> 1.) Is it normal for the notebook to spend so much time in C3, even if it
> is
> idle?
> 
> 2.) Why is an USB device screwing up the bus master activity, resulting in
> the processor never leaving C2?
> 
> 
> /Michael
> 
> 
> 
> 
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