* Re: Power managment on Overo
2010-07-15 10:29 ` Nishanth Menon
@ 2010-07-15 13:17 ` Nishanth Menon
0 siblings, 0 replies; 3+ messages in thread
From: Nishanth Menon @ 2010-07-15 13:17 UTC (permalink / raw)
To: Han Wang; +Cc: linux-omap@vger.kernel.org
Nishanth Menon had written, on 07/15/2010 05:29 AM, the following:
> On 07/15/2010 12:00 AM, Han Wang wrote:
>> Hi, All,
>>
>> I am running the linux-pm-kernel v2.35.rc3 on Overo Earth. I have managed to
>> suspend the system using "echo mem> /sys/power/state" with "enable_off_mode"
>> and "sleep_while_idle" enabled. Currently, I am able to achieve 200mW in suspend
>> mode. However, I am seen in other posts, such as this one (http://old.nabble.com/
>> Overo-boot-time--power-management-ts28402656.html#a28463135), that
>> people are able to achieve a much lower power signature.
>
> Did you check if you have actually shut off the voltages on vdd1 and
> vdd2 when you hit OFF? easy to check with a voltmeter/scope on vdd1&vdd2
> capcacitors.
Just some addon info, in case you'd like to dig further. I have'nt
personally looked at overo board, but given that it uses TWL variant
PMIC and OMAP3, the concepts should remain same, in a simplistic form:
OMAP is divided into powerdomains which power clock domains,
when the clock domains hit off, power domains switch off, if all the
domains hit off, core domain (the thing that drives sdram etc) goes to
OFF, this triggers an interesting sequence from h/w perspective -> it
toggles couple of lines - one that tells pmic that it is going to off,
and also tells the pmic that it does not need a sysclk.
twl pmic has internal scripts that can be linked to these signals- these
are called resources in PMIC terminology -> for sysoff, we have twl
scripts which tell which LDOs to switch off completely
so at OFF mode, ideally you supply 0v to vdd1,vdd2. vio_1.8 is active
and drives a domain called wakeup domain inside OMAP, this keeps a few
signals from omap and blocks within OMAP active - such as the one to
detect a wakeup event(yeah we need some mechanism to wakeup right-aka
some voltage ;) ).. the struggle is always to find the optimal
configuration for the platform at hand which minimizes the blocks and
signals active - we save a few uAmps here and there but they all add up.
Further at OFF, other than OMAP and the PMIC, there are other
peripherals on the board -e.g. if you dont need to wakeup from
Touchscreen, do we keep it on, is wlan ON? remember when you switch off
a peripheral, you need to reconfigure it to bring it back on - aka
latency tradeoff.. on a real product, there are a lot of investigations
folks do to optimize, improve the designs to achieve as little
peripherals as needed to be kept on at any given time Vs responsiveness.
in short it is usually an interesting challenge to consume as little as
possible in OFF - to use automotive language - based on the usage model,
your milage may vary ;)..
>
>> I am particularly interested to know what mode has the SDRAM on Overo been set to
>> during suspend mode? Is it auto-refresh or self-refresh? And whether the TPS/TWL
>> power management chip is set to low power mode during suspend mode by the pm
>> kernel, if not, how to set it?
>>
>> Thanks,
>> Han
>>
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--
Regards,
Nishanth Menon
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