Re: Information regarding C3 cpu state and bus mastering activity

Janosch Machowinski
2005-12-12T00:33:13Z

Marco Calviani wrote:
> Hi acpi-devel list,
> I have a problem regarding C3 states and usb. When i'm plugging in any
> usb devices, the my busmaster activity starts couting preventing the
> cpu to go to C3 state. Obviously if i unload all usb-related modules,
> C3 state goes in, my battery lives longer and the laptop stays quiter;
> unfortunately i need an usb-mouse (and possibly also an external USB drive.
> I've read somewhere that this is a specific ACPI standard behaviuor
> but i'm asking if this can be modified in some way, i.d. is it
> possible, with some workarounds, to enter C3 state also with the usb
> modules?
No this is not Possibe. In C3 the processor disables his cache. If you
have busmaster activity, there are direct writes into the cache (if I
remeber right). So if you allow C3 and Busmaster, you will get into some
serious truble and loose data.
>
> PS: i'm using a Travelmate 8005 laptop with a 1.8GHz dothan centrino
> and debian sid. i'm running kernel 2.6.12.6
>
> Thank you very much for your interest,
> Marco Calviani
>
>
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