GTA series power design

[andrzej zaborowski]

On 03/04/2008, Andy Green <andy at openmoko.com> wrote:
>  | Using e.g. the org.freesmartphone.Device.PowerManagement
> API you can
>  | then turn on and turn off the devices via dbus.
>  |
>  | (The next step on top of that would be a policy engine, so that you
>  | could express rules like
>  |  * turn on GPS every 10 minutes for until you have a fix,
>  |  * turn off WLAN if idle for 2 minutes
>  |  * turn on AUX LED on missed call or missed calendar event
>
>  It sounds good and do-able.  The only thing to note is that in future,
>  the CPU will hopefully be prone to a quite advanced case of narcolepsy,
>  it can get externally pushed into suspend at any moment... sort of
>  suffer from blackouts driven by power optimization.  It means that
>  whatever the backbone for the timer scheduling is, it needs to be a bit
>  abstracted because on these devices it may actually be queuing wake
>  timer events at the MPU, not inside Linux.

That's the design that is planned for GTA03 but it's not that of most
Linux phones, and freesmartphone as I understand it is attempting to
bring standards for the whole range of Linux smart phones, not GTA03
only.

IMHO that design with the MPU is kind of taking Linux out of the Linux
phone that Neo was planned as, making it a dumb phone with a (slightly
unneeded) cpu attached to it - Qualcomm style.  I can understand the
frustration caused by the amount of power the GTA02 is using and by
the instability of the Linux kernel having to drive very low level
stuff and at the same time bearing a whole Desktop-like userspace, but
that should get better once there's mature hardware that people can
hack on (see Zaurus).  As for the power, note that the Samsung SoC as
well as all the other popular SoCs (OMAP, Intel PXA) were designed
exactly for ultra low power operation and they are really good at it
(OMAP may be slightly more successful than S3Cxxxx), probably not much
worse than the MPU you chose, even adding the RAM power. That is, if
the software side is driving them correctly (but this is also going to
be a problem on the MPU).  The CPU may consume twenty times more power
than MPU but it's still hardly noticeable compared to the modem + LCD
backlight + everything else.

The SoC has various idle modes to make it suitable exactly for running
all the time and poking at the peripherals from time to time, that's
what it's designed for. So I don't think the new design brings that
much energy saving in daily use.  If it could be used to at least
replace the PMU then it would make more sense, but at this point you
have three processors trying to manage the power issues together.

Regards