Re: Variable ticks

[Bill Davidsen <davidsen@tmr.com>]

Brown, Len wrote:
>  
> 
>>>>Question one, are there other actions to consider?
>>>
>>>
>>>Yes.
>>>Speaking for ACPI C3 state, note that DMA also
>>>wakes up the CPU -- even if there was no device interrupt.
>>>(aka, "the trouble with USB")
>>
>>Trouble? Why would USB do DMA unless there was a device activity?
> 
> 
> look here:
> http://www.google.com/search?hl=en&q=usb+selective+suspend
> 
> Linux is working on it too, but it is in development.

Somehow I didn't ask that right... The stuff on selective disable is 
interesting, but my question is why a USB device, call it a keyboard, 
would do DMA unless I press a key, at which point response will be 
better if the CPU wakes up out of C3.

I understand that specialty attachments may send what amounts to keep 
alives, or gather data (webcam) you don't want, but the typical mouse 
and KB would seem to be things which generate DMA at user initiation, 
and would not be blocked for low power, only for suspend.
-- 
    -bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me