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From: Linus Walleij <linus.walleij@linaro.org>
Date: Tue, 2 Aug 2016 21:50:54 +0200
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To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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Cc: Gregor Boirie <gregor.boirie@parrot.com>, Zhang Rui <rui.zhang@intel.com>,
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Subject: Re: [Ksummit-discuss] [TECH TOPIC] Sensors and similar - subsystem
 interactions, divisions, bindings etc.
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On Thu, Jul 28, 2016 at 6:46 PM, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
> On Friday 22 Jul 2016 14:04:07 Linus Walleij wrote:

>> For an oscilloscope or signal analyzer usecase with more than
>> 64 channels needing to be sampled simultaneously, we may need
>> to add another "large GPIO read" ABI, and also probably a new
>> driver API interface to achieve it. I've never seen hardware that can
>> read more values in parallel than 32 though, I chose 64 to get some
>> headroom.
>
> Such a use case would put strong real-time constraints on the system, I wonder
> how useful a GPIO-based signal analyzer would be. Are you aware of any GPIO
> hardware that can be programmed to sample at a precise point in time (or
> perhaps even periodically) ?

Nope. I would expect to close the gap to IIO and reuse their trigger system
in that case, instead of creating a new one. IIO uses either hardware
trigger interrupts (usually a fixed frequency, some supply hardware
timestamps with the interrupts) or alternatively hrtimers, which in turn
would I guess be most reliable using RT patches.

Yours,
Linus Walleij