accelerometer driver

[Andy Green]

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Somebody in the thread at some point said:
| Am Di  26. August 2008 schrieb Andy Green:
|> Somebody in the thread at some point said:
|> | It seems like the accelerometers have the following:
|> |
|> | sensitive to losing an edge trigger
|>
|> We just suspect it, nobody showed it yet... it would probably be a bug
|> in the driver handling or s3c stuff rather than accelerometer "feature".
|>
|> | occur at a periodic rate
|> | access conflicts with other drivers so should be done outside of irq
|>
|> I have a nice patch coming that just does it bitbang the whole way using
|> IRQs off as locking throughout.
|>
|> | Does it make sense to just turn off the irq and have the driver use a
|> | delayed work queue to poll at a given rate?
|>
|> Interrupts are at least somewhat synchronized to the source, I think it
|> will suffer from dropped samples otherwise.  But, at some point we have
|> to take more radical measures if we don't solve it...
|
| Like general switch from edge-triggered IRQ to level-triggered.
| Edge-triggered IRQs are *NOT* suitable for physical sharing of
IRQ-line, ok we
| don't do this. Edge is more sensible to spikes and glitches, ok we
don't see
| (really?). But I expect IRQs to be locked/disabled during execution of a
| IRQ-handler (usually that's even implicit in CPU's handling of IRQs),
so only
| level-IRQ will be noticed after we exit handler.
|
| I consider usage of edge-trigger a major flaw in Openmoko-design at
large.
| Edge is used only where you can't reset the interrupt-source - like
| pushbuttons etc. I.E. async. For "sync" interrupts level is method of
choice.

Patches welcome, dude!  Get it working right and show us the way.

- -Andy


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