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