126 lines
4.0 KiB
ReStructuredText
126 lines
4.0 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
=========================
|
|
i.MX Video Capture Driver
|
|
=========================
|
|
|
|
Events
|
|
======
|
|
|
|
.. _imx_api_ipuX_csiY:
|
|
|
|
ipuX_csiY
|
|
---------
|
|
|
|
This subdev can generate the following event when enabling the second
|
|
IDMAC source pad:
|
|
|
|
- V4L2_EVENT_IMX_FRAME_INTERVAL_ERROR
|
|
|
|
The user application can subscribe to this event from the ipuX_csiY
|
|
subdev node. This event is generated by the Frame Interval Monitor
|
|
(see below for more on the FIM).
|
|
|
|
Controls
|
|
========
|
|
|
|
.. _imx_api_FIM:
|
|
|
|
Frame Interval Monitor in ipuX_csiY
|
|
-----------------------------------
|
|
|
|
The adv718x decoders can occasionally send corrupt fields during
|
|
NTSC/PAL signal re-sync (too little or too many video lines). When
|
|
this happens, the IPU triggers a mechanism to re-establish vertical
|
|
sync by adding 1 dummy line every frame, which causes a rolling effect
|
|
from image to image, and can last a long time before a stable image is
|
|
recovered. Or sometimes the mechanism doesn't work at all, causing a
|
|
permanent split image (one frame contains lines from two consecutive
|
|
captured images).
|
|
|
|
From experiment it was found that during image rolling, the frame
|
|
intervals (elapsed time between two EOF's) drop below the nominal
|
|
value for the current standard, by about one frame time (60 usec),
|
|
and remain at that value until rolling stops.
|
|
|
|
While the reason for this observation isn't known (the IPU dummy
|
|
line mechanism should show an increase in the intervals by 1 line
|
|
time every frame, not a fixed value), we can use it to detect the
|
|
corrupt fields using a frame interval monitor. If the FIM detects a
|
|
bad frame interval, the ipuX_csiY subdev will send the event
|
|
V4L2_EVENT_IMX_FRAME_INTERVAL_ERROR. Userland can register with
|
|
the FIM event notification on the ipuX_csiY subdev device node.
|
|
Userland can issue a streaming restart when this event is received
|
|
to correct the rolling/split image.
|
|
|
|
The ipuX_csiY subdev includes custom controls to tweak some dials for
|
|
FIM. If one of these controls is changed during streaming, the FIM will
|
|
be reset and will continue at the new settings.
|
|
|
|
- V4L2_CID_IMX_FIM_ENABLE
|
|
|
|
Enable/disable the FIM.
|
|
|
|
- V4L2_CID_IMX_FIM_NUM
|
|
|
|
How many frame interval measurements to average before comparing against
|
|
the nominal frame interval reported by the sensor. This can reduce noise
|
|
caused by interrupt latency.
|
|
|
|
- V4L2_CID_IMX_FIM_TOLERANCE_MIN
|
|
|
|
If the averaged intervals fall outside nominal by this amount, in
|
|
microseconds, the V4L2_EVENT_IMX_FRAME_INTERVAL_ERROR event is sent.
|
|
|
|
- V4L2_CID_IMX_FIM_TOLERANCE_MAX
|
|
|
|
If any intervals are higher than this value, those samples are
|
|
discarded and do not enter into the average. This can be used to
|
|
discard really high interval errors that might be due to interrupt
|
|
latency from high system load.
|
|
|
|
- V4L2_CID_IMX_FIM_NUM_SKIP
|
|
|
|
How many frames to skip after a FIM reset or stream restart before
|
|
FIM begins to average intervals.
|
|
|
|
- V4L2_CID_IMX_FIM_ICAP_CHANNEL / V4L2_CID_IMX_FIM_ICAP_EDGE
|
|
|
|
These controls will configure an input capture channel as the method
|
|
for measuring frame intervals. This is superior to the default method
|
|
of measuring frame intervals via EOF interrupt, since it is not subject
|
|
to uncertainty errors introduced by interrupt latency.
|
|
|
|
Input capture requires hardware support. A VSYNC signal must be routed
|
|
to one of the i.MX6 input capture channel pads.
|
|
|
|
V4L2_CID_IMX_FIM_ICAP_CHANNEL configures which i.MX6 input capture
|
|
channel to use. This must be 0 or 1.
|
|
|
|
V4L2_CID_IMX_FIM_ICAP_EDGE configures which signal edge will trigger
|
|
input capture events. By default the input capture method is disabled
|
|
with a value of IRQ_TYPE_NONE. Set this control to IRQ_TYPE_EDGE_RISING,
|
|
IRQ_TYPE_EDGE_FALLING, or IRQ_TYPE_EDGE_BOTH to enable input capture,
|
|
triggered on the given signal edge(s).
|
|
|
|
When input capture is disabled, frame intervals will be measured via
|
|
EOF interrupt.
|
|
|
|
|
|
File list
|
|
---------
|
|
|
|
drivers/staging/media/imx/
|
|
include/media/imx.h
|
|
include/linux/imx-media.h
|
|
|
|
|
|
Authors
|
|
-------
|
|
|
|
- Steve Longerbeam <steve_longerbeam@mentor.com>
|
|
- Philipp Zabel <kernel@pengutronix.de>
|
|
- Russell King <linux@armlinux.org.uk>
|
|
|
|
Copyright (C) 2012-2017 Mentor Graphics Inc.
|