CL1B power distribution

John Watlington wad at
Sat Apr 25 01:59:41 EDT 2009

On Apr 25, 2009, at 1:06 AM, Albert Cahalan wrote:

> John Watlington writes:
>> - The SD slot and USB ports may be powered in suspend
>>      This is "just in case" some SD cards or USB devices don't handle
>> being suspended
>>      aggressively.   We will support laptop wakeup on interrupt  
>> from any
>>      of these ports (SD or USB).   Under software control they may
>> also be powered
>>      down during suspend.
> There is value in making this per-port for the USB.

Funny, there was just a discussion of this on olpc-devel IRC.
There are several reasons not to use individual port switches:
- cost
- each USB port would then be limited to 2.5W (or 1.6W), instead
of the 5W possible now.
- cost
- cost

>> - The audio codec remains partially powered in suspend
>>      This is in order to support "wakeup on jack insertion".  The  
>> codec
>>      may be placed in a very low power state during suspend.
> I would have expected power to be optional. The software doesn't
> always need to use this component during the run state

It can be placed in the same low power state during run (when
not used) as during suspend...

>> Additional changes from Gen 1 include the ability to both measure
>> DC input current and VIN voltage, as well as EC control over the
>> current drawn from the DC input. The intent was to better support
>> charging directly from solar panels.
> I hope that this will be available to activities like Measure.

Interesting point.  That would require extending the EC API, as they  
go to an A/D
not directly addressable by the main processor.

> Ideally updates could be frequent enough to pick up a waveform
> from an unrectified power supply. (spare audio channel?)


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