1.. SPDX-License-Identifier: GPL-2.0 2 3========================= 4i.MX Video Capture Driver 5========================= 6 7Events 8====== 9 10.. _imx_api_ipuX_csiY: 11 12ipuX_csiY 13--------- 14 15This subdev can generate the following event when enabling the second 16IDMAC source pad: 17 18- V4L2_EVENT_IMX_FRAME_INTERVAL_ERROR 19 20The user application can subscribe to this event from the ipuX_csiY 21subdev node. This event is generated by the Frame Interval Monitor 22(see below for more on the FIM). 23 24Controls 25======== 26 27.. _imx_api_FIM: 28 29Frame Interval Monitor in ipuX_csiY 30----------------------------------- 31 32The adv718x decoders can occasionally send corrupt fields during 33NTSC/PAL signal re-sync (too little or too many video lines). When 34this happens, the IPU triggers a mechanism to re-establish vertical 35sync by adding 1 dummy line every frame, which causes a rolling effect 36from image to image, and can last a long time before a stable image is 37recovered. Or sometimes the mechanism doesn't work at all, causing a 38permanent split image (one frame contains lines from two consecutive 39captured images). 40 41From experiment it was found that during image rolling, the frame 42intervals (elapsed time between two EOF's) drop below the nominal 43value for the current standard, by about one frame time (60 usec), 44and remain at that value until rolling stops. 45 46While the reason for this observation isn't known (the IPU dummy 47line mechanism should show an increase in the intervals by 1 line 48time every frame, not a fixed value), we can use it to detect the 49corrupt fields using a frame interval monitor. If the FIM detects a 50bad frame interval, the ipuX_csiY subdev will send the event 51V4L2_EVENT_IMX_FRAME_INTERVAL_ERROR. Userland can register with 52the FIM event notification on the ipuX_csiY subdev device node. 53Userland can issue a streaming restart when this event is received 54to correct the rolling/split image. 55 56The ipuX_csiY subdev includes custom controls to tweak some dials for 57FIM. If one of these controls is changed during streaming, the FIM will 58be reset and will continue at the new settings. 59 60- V4L2_CID_IMX_FIM_ENABLE 61 62Enable/disable the FIM. 63 64- V4L2_CID_IMX_FIM_NUM 65 66How many frame interval measurements to average before comparing against 67the nominal frame interval reported by the sensor. This can reduce noise 68caused by interrupt latency. 69 70- V4L2_CID_IMX_FIM_TOLERANCE_MIN 71 72If the averaged intervals fall outside nominal by this amount, in 73microseconds, the V4L2_EVENT_IMX_FRAME_INTERVAL_ERROR event is sent. 74 75- V4L2_CID_IMX_FIM_TOLERANCE_MAX 76 77If any intervals are higher than this value, those samples are 78discarded and do not enter into the average. This can be used to 79discard really high interval errors that might be due to interrupt 80latency from high system load. 81 82- V4L2_CID_IMX_FIM_NUM_SKIP 83 84How many frames to skip after a FIM reset or stream restart before 85FIM begins to average intervals. 86 87- V4L2_CID_IMX_FIM_ICAP_CHANNEL / V4L2_CID_IMX_FIM_ICAP_EDGE 88 89These controls will configure an input capture channel as the method 90for measuring frame intervals. This is superior to the default method 91of measuring frame intervals via EOF interrupt, since it is not subject 92to uncertainty errors introduced by interrupt latency. 93 94Input capture requires hardware support. A VSYNC signal must be routed 95to one of the i.MX6 input capture channel pads. 96 97V4L2_CID_IMX_FIM_ICAP_CHANNEL configures which i.MX6 input capture 98channel to use. This must be 0 or 1. 99 100V4L2_CID_IMX_FIM_ICAP_EDGE configures which signal edge will trigger 101input capture events. By default the input capture method is disabled 102with a value of IRQ_TYPE_NONE. Set this control to IRQ_TYPE_EDGE_RISING, 103IRQ_TYPE_EDGE_FALLING, or IRQ_TYPE_EDGE_BOTH to enable input capture, 104triggered on the given signal edge(s). 105 106When input capture is disabled, frame intervals will be measured via 107EOF interrupt. 108 109 110File list 111--------- 112 113drivers/staging/media/imx/ 114include/media/imx.h 115include/linux/imx-media.h 116 117 118Authors 119------- 120 121- Steve Longerbeam <steve_longerbeam@mentor.com> 122- Philipp Zabel <kernel@pengutronix.de> 123- Russell King <linux@armlinux.org.uk> 124 125Copyright (C) 2012-2017 Mentor Graphics Inc. 126