Better characterization of suspend current

Andy Green andy at
Tue Feb 12 07:56:04 CET 2008

Hash: SHA1

Somebody in the thread at some point said:
> 於 五,2008-02-08 於 09:25 +0000,Andy Green 提到:
> Hi folks -
> I was lying awake in bed at 3.30am musing about the suspend current.
> The smart battery says on it that it is "3.7V 1250mAh", so naturally I
> divided 1250 / 5 and I say to myself "wah!  Does it really mean we have
> a 250hr standby time now?  Didn't I see that kind of number on adverts
> for mobile phones?  
>> 	Well, we had tried to measure the suspend current of Touch which from
>> HTC. Its suspend current is dropped between 3mA~4mA. In addition, its
>> resuming is pretty fast.

Right now my phone resumes real fast into complete death :-)

> 10 days?  Cool!"  Then doubts and suspicion crowded
> around me in the dark.
>  - This "5mA" figure never got tied to any specific configuration I saw,
> it just got reported as a single figure.  That needs specifying so the
> tests are repeatable and can be understood in context. 
>> 	Sure. It's necessary to have many repeatable and abnormal tests. So
>> automated power measuring is the right thing to do. ;-)

Well just specifying the conditions for each measurement is a good start :-)

>  For example,
> what are we measuring here?  It is Vb at the battery terminal, right?
>  - The GSM modem seems to be "off" according to Allen's last attack on
> the current monster.  Is it off?  What happens to suspend current when
> it is left on so in can wake on incoming call?  
>> 	That's the next question I would like to know. 
>> 	I think we could figure this out these days. But I need GSM people to
>> help out.   

Alright, but then we have to wonder if the HTC phone has its GSM module
on when you measured it as a baseline to compare against.  It means we
still have work to do if we get 5mA with ours off and they get 3-4mA
with theirs on.

>  - People avoided using batteries and use bench PSUs last I saw (hence
> nobody told me about charging completely broken).  What is the situation
> there for this measurement?  It matters because -->
>> 	I sent this patch before. 

Well I have to apologize for not taking care about your patches, you
found the charger enable problem already before I looked at it and
clearly had charging working first -- so well done.  I guess if Werner
didn't take the U-Boot one already he should, I didn't look at charging
in U-Boot.

>> 	Yes. The system would be shutdown immediately when the battery is about
>> 3v3. I think we could add some detecting and handling at u-boot to avoid
>> booting up when system tends less voltage.

A problem here could that if we read -- and clear -- the PMU INT# stuff
in U-Boot (to get LOWBAT) the general coldplug actions driven by
inheriting the INT# bits will be broken in Linux.  Well with the
patchset I sent yesterday we take care of it in early Linux boot anyway
and shut down in that condition.

> be arrived at from these measurements, and we need to check that
> lifetime on a real phone actually left in standby until it flakes out.

>> 	It sounds great. I will let HW people to know this suggestion and to
>> see any possibilities to have this observation. 


- -Andy
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