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Message-ID: <20230316030755.GC1927922@google.com>
Date: Thu, 16 Mar 2023 12:07:55 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Sergey Senozhatsky <senozhatsky@...omium.org>,
linux-kernel@...r.kernel.org, "hn.chen" <hn.chen@...plusit.com>,
linux-media@...r.kernel.org
Subject: Re: [PATCH v9 6/6] media: uvcvideo: Fix hw timestamp handling for
slow FPS
On (23/03/15 14:30), Ricardo Ribalda wrote:
> In UVC 1.5 we get a single clock value per frame. With the current
> buffer size of 32, FPS slowers than 32 might roll-over twice.
>
> The current code cannot handle two roll-over and provide invalid
> timestamps.
>
> Revome all the samples from the circular buffer that are more than two
> rollovers old, so the algorithm always provides good timestamps.
>
> Note that we are removing values that are more than one second old,
> which means that there is enough distance between the two points that
> we use for the interpolation to provide good values.
>
> Tested-by: HungNien Chen <hn.chen@...plusit.com>
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@...omium.org>
[..]
> + if (clock->count > 0 && clock->last_sof > sample->dev_sof) {
> + /*
> + * Remove data from the circular buffer that is older than the
> + * last overflow. We only support one overflow per circular
> + * buffer.
> + */
> + if (clock->last_sof_overflow != -1) {
> + clock->count = (clock->head - clock->last_sof_overflow
> + + clock->count) % clock->count;
A minor nit: there is a tab between `clock->count)` and `% clock->count` :)
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