On 03/04/2017 02:56 AM, Sakari Ailus wrote:
Hi Steve,
On Fri, Mar 03, 2017 at 02:43:51PM -0800, Steve Longerbeam wrote:
On 03/03/2017 03:45 AM, Sakari Ailus wrote:
On Thu, Mar 02, 2017 at 03:07:21PM -0800, Steve Longerbeam wrote:
On 03/02/2017 07:53 AM, Sakari Ailus wrote:
Hi Steve,
On Wed, Feb 15, 2017 at 06:19:15PM -0800, Steve Longerbeam wrote:
Add a new FRAME_TIMEOUT event to signal that a video capture or
output device has timed out waiting for reception or transmit
completion of a video frame.
Signed-off-by: Steve Longerbeam <steve_longerbeam@xxxxxxxxxx>
---
Documentation/media/uapi/v4l/vidioc-dqevent.rst | 5 +++++
Documentation/media/videodev2.h.rst.exceptions | 1 +
include/uapi/linux/videodev2.h | 1 +
3 files changed, 7 insertions(+)
diff --git a/Documentation/media/uapi/v4l/vidioc-dqevent.rst b/Documentation/media/uapi/v4l/vidioc-dqevent.rst
index 8d663a7..dd77d9b 100644
--- a/Documentation/media/uapi/v4l/vidioc-dqevent.rst
+++ b/Documentation/media/uapi/v4l/vidioc-dqevent.rst
@@ -197,6 +197,11 @@ call.
the regions changes. This event has a struct
:c:type:`v4l2_event_motion_det`
associated with it.
+ * - ``V4L2_EVENT_FRAME_TIMEOUT``
+ - 7
+ - This event is triggered when the video capture or output device
+ has timed out waiting for the reception or transmit completion of
+ a frame of video.
As you're adding a new interface, I suppose you have an implementation
around. How do you determine what that timeout should be?
The imx-media driver sets the timeout to 1 second, or 30 frame
periods at 30 fps.
The frame rate is not necessarily constant during streaming. It may well
change as a result of lighting conditions.
I think you mean that would be a _temporary_ change in frame rate, but
yes I agree the data rate can temporarily fluctuate. Although I doubt
lighting conditions would cause a sensor to pause data transmission
for a full 1 second.
Likely not, at least not in typical conditions. The exposure time is still
quite specific to applications: it could be minutes if you take photos e.g.
of the night sky.
What I'm saying here is that any static value is likely not both reasonable
and workable in all potential situations all the time. Still there are cases
(as yours below) that may happen in relatively common cases on some hardware
(more common than taking long exposure photos of the night sky with the said
hardware :)).
I doubt night photography will ever be a use-case for i.MX. The most
common use-case for this driver will be used in automotive applications
such as rear-view or 360 degree view cameras.
I wouldn't add an event for this:
this is unreliable and 30 times the frame period is an arbitrary value
anyway. No other drivers do this either.
If no other drivers do this I don't mind removing it. It is really meant
to deal with the ADV718x CVBS decoder, which often simply stops sending
data on the BT.656 bus if there is an interruption in the input analog
signal. But I agree that user space could detect this timeout instead.
Unless I hear from someone else that they would like to keep this
feature I'll remove it in version 5.
That's a bit of a special situation --- still there are alike conditions on
existing hardware. You should return the buffers to the user with the ERROR
flag set --- or return -EIO from VIDIOC_DQBUF, if the condition will
persist:
On i.MX an EOF timeout is not recoverable without a stream restart, so
I decided to call vb2_queue_error() when the timeout occurs (instead
of sending an event). The user will then get -EIO when it attempts to
queue or dequeue further buffers.
<URL:https://www.linuxtv.org/downloads/v4l-dvb-apis/uapi/v4l/vidioc-qbuf.html>
Do you already obtain the frame rate from the image source (e.g. tuner,
sensor, decoder) and multiply the frame time by some number in the current
implementation?
No the timeout is a constant value, regardless of the source frame
rate. Should the timeout be based on a constant time, or based on a
constant # of frames? I really don't think it matters much, what matters
is that it be long enough to be reasonably sure no data is forthcoming,
for most use-cases.
Steve
Not all sub-device drivers may implement g_frame_interval()
so I'd disable the timeout in that case.
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