[Gta04-owner] Current consumption during suspend

NeilBrown neilb at suse.de
Mon Aug 27 12:50:53 CEST 2012

On Sat, 25 Aug 2012 19:29:09 +0200 "Dr. H. Nikolaus Schaller"
<hns at goldelico.com> wrote:

> > Further observations: If the sleep current is not somewhere around
> > 20mA but near 25mA the ITG-3200 may caused the additional power
> > consumption. There seem to be a few cases where the chip isn't reset
> I know one case where it happens for sure: if you connect USB power
> without battery, the device will not visibly boot. Rather it will try to boot,
> but shuts down after some 100-500 ms. This makes the ITG state machine
> run into "no-response" mode. Even if you insert the battery later and the
> device finally boots.
> If you put in the battery first and the USB power next, it will properly
> reset.
> > correctly which causes its I2C interface to malfunction and therefore
> I2C will timeout in this situation.
> In this case it should be possible to shortly pulse off the VAUX that
> powers the sensors. Although this makes the ITG being operated outside
> of the spec shortly (VIO > VDD) it resets the chip. This is IMHO acceptable
> since the VAUX LDO is current limited and is only a fallback for the rare
> case that the ITG does no longer respond.
> This could be hacked into the driver - although it makes it *very* specific
> to the GTA04 boards and probably nobody else needs it in a ITG3200
> driver.
> @NeilBrown: is it possible that the ITG3200 can notify the board file
> or some VAUX regulator just about the I2C timeout? So that generating
> the emergency reset is clearly separated from the driver?

I can't immediately think of a neat way to do this.  The ITG3200 driver
doesn't get called at all until the I2C bus find a device with the right
signature, so if the ITG3200 isn't responding properly to that first problem,
there is nothing we can do in it's driver to trigger a reset.

May we could arrange to always reset the sensors on boot.  i.e. do it
completely in the board file...

What exactly is the symptom here?  How reproducible is it?  Can you reproduce
with a sequence of warm reboots or do you need to remove and re-add power.
i.e. how can I test a possible fix to see if it makes a difference?

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