No C4 State with Powertop

[Arjan van de Ven]

bi0 wrote:
> Hi,
> 
> I'm wondering why there is no C4 state available on my Macbook with an
> Intel Core Duo. There are
> only the states C0-3 shown.
> 
> I thought this might be a general problem in linux, but the example on
> the website (linuxpowertop.org/powertop.php)
> shows a C4 state.
>

Hi,

it depends on your BIOS. Some bioses don't enable C4 when you're on AC 
(mains) power, but only when you're on battery. Other bioses silently 
remap C3 to be hardware-C4 when you're on battery, and will never show 
C4, even though it'll go to C4 when Linux asks for C3 when on battery..

yes I know it's confusing.. I'll see if I can write up a small article 
about this with information