| .. 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. |
