[PATCH 3/3] fix-lis302dl-dont-reset-hpf-each-time.patch

Simon Kagstrom simon.kagstrom at gmail.com
Tue Feb 3 11:24:46 CET 2009

On Tue, 03 Feb 2009 10:00:17 +0000
Andy Green <andy at openmoko.com> wrote:

> | The threshold stuff needs this reset to work, but I suppose we could
> | add a check if the threshold is actually set before resetting the HP
> | filter. I don't think it affects "interrupt-on-every-datum" mode
> | anyway.
> What happens if we leave the HP filter un-reset with threshold?  It
> sounds like it should only make it harder to reach the threshold, not
> break things?

I don't quite remember, but I think it was that the threshold is
checked relative to the last time the filter was reset, so if you don't
reset it you won't get any more data.  Unfortunately the data sheet is not
overly clear about how the HP filter is actually supposed to work.

It caused a bit of headache when developing since the HP filter is
reset when reading. Thus, the device would generate data once again
when the debug sysfs node is read.

> You're right the comment about reset HPF made it look like they're
> related.  But that one too is only needed if there's a threshold
> wakeup.

Sorry about that. It might not even be needed then, since there is some
"auto-ack" option that can be set.

// Simon

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