Re: [PATCH v4 3/6] Documentation: DT: Document twl4030-madc-battery bindings

Pavel Machek
2015-04-04T08:17:04Z

Hi!

> >> Please propose your own code doing that so that we can test if it is
> >> better.
> >
> > So, how does this look?
> >
> > It looks to me like you have cca 0.1 Ohm resistance in your system,
>
> This is completely unknown.
>
> > and are using cca 75mA while discharging, and charge by cca 1.4A.
>
> Where do you get these figures from?

Least squares fitting of my coefficients to your tables.

> A GTA04 board discharges usually between 50 and 400 mA (depending on activities)
> and if you turn on WiFi, it will be up to 600 mA. If you use 3G it can draw even more
> during operation.

How big battery do you have? According to least squares fitting,
assuming maximum charge of .46A, you were taking about 25mA when
doing the discharge test.

> Total current going in is 500-800 mA (depending on USB negotiations) and this is
> split into system operation and charging current. So 1.4A charging current is not
> possible. Rather 200-500 mA.
>
> So it might be that the battery is discharged although the system is connected
> to a charger.

Yah, and your battery meter will be wrong in such case, as will be
mine, because they are based on same information. The thing is, mine
can be improved without adding more tables.

> > It is tricky to do a good job near 0%... or anywhere else. See for
> > example
> >
> > http://cseweb.ucsd.edu/~trosing/lectures/battery.pdf
> >
> > You start a call, percentage goes down, end a call, it will go
> > back up. I'm pretty sure you will not be able to make a call with "5%"
> > indication from your code at low battery temperature (say -10C).
>
> The whole system is heating up a little, so that you never have -10C for the
> battery.

Umm. When not calling, your phone should not heat itself up. And you
definitely can power it down, leave it in outer pocket, then power it
up. It is actually something people do when they want to preserve battery...

> I think you are trying to solve situations that don’t exist in practice.
>
> And AFAIK, the GTA04 board is the only user of this driver in case the battery
> has no built-in fuel gauge. So why improve it beyond what the GTA04
> users need?

Because then other users can share the same code, and because you
avoid big ugly tables in dts.

> I repeat myself: this driver is not built for highest precision because there are
> better methods (fuel gauge chip). These might not be available so this fall-back
> driver has been built.
>
> It is definitively better than no driver and worse than the optimum.

And my email suggested solution better than your driver, so why not
just use it?

> > #perc = percent(volt)
> > compute(charging, 1)
> > compute(discharging, 0)
>
> Please explain what you calculate here. Especially what “Badness” is?

Badness is error in least squares method.

Here are updated tables:

pavel@duo:~/g/tui/ofone$ ./liion_maps
Charging
Voltage 4.2 V ; table 100 % internal voltage 4.18 V current 0.078 A computed 97 %
Voltage 4.1 V ; table 75 % internal voltage 4.08 V current 0.078 A computed 87 %
Voltage 4.0 V ; table 55 % internal voltage 3.93 V current 0.233 A computed 69 %
Voltage 3.9 V ; table 25 % internal voltage 3.76 V current 0.467 A computed 26 %
Voltage 3.8 V ; table 5 % internal voltage 3.66 V current 0.467 A computed 3 %
Voltage 3.7 V ; table 2 % internal voltage 3.56 V current 0.467 A computed 2 %
Voltage 3.6 V ; table 1 % internal voltage 3.46 V current 0.467 A computed 1 %
Voltage 3.3 V ; table 0 % internal voltage 3.16 V current 0.467 A computed -1 %
Badness 395.4861761427434
Discharging
Voltage 4.2 V ; table 100 % internal voltage 4.21 V current -0.025 A computed 100 %
Voltage 4.1 V ; table 95 % internal voltage 4.11 V current -0.025 A computed 91 %
Voltage 4.0 V ; table 70 % internal voltage 4.01 V current -0.025 A computed 79 %
Voltage 3.8 V ; table 50 % internal voltage 3.81 V current -0.025 A computed 46 %
Voltage 3.7 V ; table 10 % internal voltage 3.71 V current -0.025 A computed 3 %
Voltage 3.6 V ; table 5 % internal voltage 3.61 V current -0.025 A computed 2 %
Voltage 3.3 V ; table 0 % internal voltage 3.31 V current -0.025 A computed 0 %
Badness 171.69576218433212
pavel@duo:~/g/tui/ofone$ python

Pavel

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