[Openec] RFC: One-Wire-Filesystem (owfs) for charging battery on XO and openec, (long)

[Frieder Ferlemann]

Hi Albert,

"Albert Cahalan" <acahalan at gmail.com> schrieb am 02.09.2007 23:06:30:
> > The One-Wire-Filesystem allows to access data on 1-wire devices
> > as if they were a file within a directory.
> 
> nice for debugging

Yes, it would be nice to have owfs on the XO communicate via external
adapters (f.e. around adapters that build around the DS2490, or the
4 diode, 1 resistor solution in the middle of http://owfs.sourceforge.net/adapters.html)

Also it would be nice if the EC (with the commands as they are now) would
appear as an adapter to owfs. 

With mass production imminent I feel that the proposal may have hit an unfortunate time.

> > A task in linux user space would periodically (and/or on
> > notification) read the data from the appropriate files
> > and based on that give directions to the EC.
> 
> Polling is terrible. Waking up the CPU is not much better.

There should be long (say 10s/minute) intervals where the EC
could run unattended with the directions it has been given.
Depends on the charging algorithm.

Typically if there is enough power to switch into low speed
or high speed charging waking the CPU should not be too harmful.
(does waking the CPU change the charge current into the
battery?)

 
> > These directions would tell the EC what to do now and
> > what to do next.
> 
> Watch out here. Battery condition might suddenly change.
> One might even swap batteries.

No chance openec will miss that:)
(The higher levels will notice too, as the device appear under
there unique ID in the owfs directory)
 
> Consider also the problem of human-powered start-up
> from a fully drained battery.

Yes, there would have to be a kind of bootstrap mode.

> > The resources within the EC are pretty low (RAM is 128 byte
> > idata memory, 2kByte xdata memory).
> > While one can it is not really a good idea to have floating
> > point operations on the EC. (Linux kernel does not either)
> > The 2kByte do not allow an elaborated charging algorithm
> > to use a longer history.
> 
> Note that the gang charger idea also suffers here.
> Charging without the OS means charging without
> a battery history. Battery changes are trouble too.
> One might save battery history on the school server,
> but watch out for malicious history.
> 
> It's nice to charge without booting Linux.

(In case of XO it will already booted?)

Greetings,
Frieder
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