Power consumption and rectification

Wolfgang Spraul wolfgang at qi-hardware.com
Fri Nov 6 11:29:25 EST 2009


Bas,

> - When the device is on, with the display enabled, it uses 123 mA.
> - When the device is on, with the display disabled, it uses 37 mA.
> - When the device is off, it uses 4.5 mA.

Interesting numbers.
There is definitely a lot in what we can do to squeeze our longer battery
life under various loads.
The CPU is running at the full 336 MHz I guess. I am wondering in which
increments and how low we can lower the CPU clock?
Can we enable/disable some other domains/controllers in the CPU?
4.5mA for the 'off' state sounds quite high, I am wondering whether this
can be optimized as well.

Anyway, your measurements bring a lot of clarity, very nice!
Wolfgang

On Fri, Nov 06, 2009 at 12:14:44AM +0100, Bas Wijnen wrote:
> Hi,
> 
> I have measured the power consumption of the device, by removing the
> battery and tapping the usb cable, insering a current and voltage meter
> in it.  I found the following:
> 
> - When the device is on, with the display enabled, it uses 123 mA.
> - When the device is on, with the display disabled, it uses 37 mA.
> - When the device is off, it uses 4.5 mA.
> 
> The device used 4.7 V during the measurement.  The battery that came
> with it says 4.2 V, 850 mAh.
> 
> This leads to the following times:
> - on with display: 6.2 hours.
> - on without display: 20.5 hours.
> - off: 7.0 days.
> 
> "on without display" is the state where it's waiting for a connection in
> usb boot mode (with the auo display, which is off by default).  No
> devices are enabled.  In particular, this is probably not a good
> estimate for how long it can be used to play sound files.
> 
> Also, these times are computed from what the battery says it can do; I
> expect actual values to be slightly lower (and much lower when the
> battery gets older, of course).
> 
> This measurement leads to a short rectification:
> 
> On Sat, Oct 31, 2009 at 10:19:29AM +0100, Bas Wijnen wrote:
> > - Warning: when booting Iris in its current state, the lcd will switch
> >   on and display nonsense.  Leaving it on for a minute or so makes the
> >   device unbootable for some time (probably until it cooled down).  I
> >   don't know if this is harmful for the device, so don't try.
> 
> There is no problem.  The device was sometimes on and sometimes off when
> I replugged it.  If it became unbootable, it was off.  Pressing the
> power button made it work again.  I'm pretty sure there is no damage at
> all, even if the display is left like this for a longer time (not that
> that's very useful...).
> 
> Thanks,
> Bas



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