Michael Kenney escreveu:
> On Nov 15, 2007 8:11 PM, thaGod <thagod@...> wrote:
>> You want to lower a 400MHz system to *under* 1.4W?
> There are a few of us who very much desire < 1W systems. Many
> remotely deployed data-logging systems used in oceanographic research
> have very tight power constraints.
> I have found that a 400mhz Verdex + netCF board with the ethernet
> interface disabled draws about 55mA @ 5v with the CPU idle. Reading
> and writing to the CF card spikes the current up to 80-100mA. These
> aren't bad numbers but I would like to do even better. I have been
> playing with the 'standby' and 'suspend to RAM' modes. Standby
> dropped the current to 25-30mA but suspend-to-RAM actually *increased*
> the current to > 60mA -- clearly there is something wrong here.
As far as I can recall, the pxa series has a register which sets all the
GPIOs to some mode and state when entering the deep sleep mode. If that
is not set right, it could be that some pins physically tied to the
ground or to vcc would get the opposite logical setting during idle
time, which would make then power hogs. The exact setting is probably a
default, generic one, which is not tuned from the linux kernel drivers,
it has to be provided by the implementation (i.e. the gumstix patches).
A single GPIO in a situation like that could lead to some considerable
power consuption. Even if a pin in special function gets in tristate it
could lead to external hardware to misbehave (i.e. awake) and consume power.
That's one possibility to account for, certainly there are others.
> For my current project, 55mA at idle easily meets the requirements but
> for a potential future project it would be nice to be able to "sleep"
> the system at < 10mA and wakeup in 1-2 seconds.
Depending on the verdex board design, I would risk saying that it's
possible to achieve that even without deep sleep, just by lowering the
cpu and memory clocks and disabling both unneeded pxa's internal
periferals and external ones.
There's a power management µc on the board, it may have some interesting
On the connex series, power management is much less capable; with very
low voltage (3.7v I think)
and a 100mhz clock, I could get around 30ma when idle. The cpufreq gives
trouble on the pxa 255, but that's ok on the verdex.