examples/uvc_cam: add UVC camera streaming app

[JianyuWang0623]

Summary

Add a UVC camera streaming example application (examples/uvc_cam) that captures frames from a V4L2 camera sensor and streams them to a USB host via the UVC gadget driver.

The application:

• Queries the sensor's native pixel format, resolution, and frame rate dynamically via VIDIOC_ENUM_FMT, VIDIOC_ENUM_FRAMESIZES, and VIDIOC_ENUM_FRAMEINTERVALS — no hardcoded video parameters.
• Initializes/deinitializes the UVC gadget through boardctl(BOARDIOC_USBDEV_CONTROL).
• Uses poll() with POLLOUT to wait for the USB host to start streaming, and to detect host disconnect/reconnect.
• Supports optional positional arguments: uvc_cam [nframes] [video_dev] [uvc_dev].
• Supports configurable frame count via Kconfig (CONFIG_EXAMPLES_UVC_CAM_NFRAMES, 0 = infinite).

Depends on the nuttx UVC gadget class driver (apache/nuttx#18609).

Impact

New example application only. No impact on existing code or build.

Adds Kconfig symbol CONFIG_EXAMPLES_UVC_CAM (depends on USBUVC), with sub-options for program name, priority, stack size, and frame count.

Testing

• Host: Ubuntu 22.04 x86_64, GCC 13.2.0 (Xtensa esp32s3 cross-compiler)
• Target: xtensa lckfb-szpi-esp32s3:uvc
• Build: make distclean && ./tools/configure.sh lckfb-szpi-esp32s3:uvc && make -j$(nproc) — clean build, zero warnings.
• Runtime: Flashed to ESP32-S3 board with GC0308 camera sensor. Verified 320×240 YUYV streaming to Linux host — frames displayed correctly via ffplay -f v4l2 -video_size 320x240 -i /dev/video1. Verified host disconnect/reconnect recovery.

[cederom]

Awesome! @JianyuWang0623 could you also please add Documentation on how to use this application as part of documentation in apache/nuttx#18609 bundle? :-)

[JianyuWang0623]

Awesome! @JianyuWang0623 could you also please add Documentation on how to use this application as part of documentation in apache/nuttx#18609 bundle? :-)

@cederom Will do! I’ve just added the usage documentation here: https://github.com/apache/nuttx/compare/9d2ec9642d7bf0c41699f104c06948febeac64b4..e4babac55082a02feef90ad9ed128a5c5ad84648

[cederom]

Awesome! @JianyuWang0623 could you also please add Documentation on how to use this application as part of documentation in apache/nuttx#18609 bundle? :-)

@cederom Will do! I’ve just added the usage documentation here: https://github.com/apache/nuttx/compare/9d2ec9642d7bf0c41699f104c06948febeac64b4..e4babac55082a02feef90ad9ed128a5c5ad84648

TANK U SIR! =)

[simbit18]

@JianyuWang0623 This error is not related to this PR

You will need to wait for this PR #3440 to be merged, after which you will need to rebase

====================================================================================
Configuration/Tool: sim/citest
2026-03-27 02:48:55
------------------------------------------------------------------------------------
  Cleaning...
  Configuring...
  Building NuttX...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
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  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed

  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0

  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
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100 1646k  100 1646k    0     0  3078k      0 --:--:-- --:--:-- --:--:-- 5899k

100  143k    0  143k    0     0   286k      0 --:--:-- --:--:-- --:--:--  286k
  Running NuttX...
++ pwd
+ olddir=/github/workspace/sources/nuttx
+ nuttdir=/github/workspace/sources/nuttx/boards/sim/sim/sim/configs/citest/../../../../../../
+ cd /github/workspace/sources/nuttx/boards/sim/sim/sim/configs/citest/../../../../../../
+ confpath=/github/workspace/sources/nuttx/boards/sim/sim/sim/configs/citest/config.yaml
+ jsonconf=/github/workspace/sources/nuttx/boards/sim/sim/sim/configs/citest/session.json
+ testpath=/github/workspace/nuttx-ntfc/external/nuttx-testing
+ ntfc test --testpath=/github/workspace/nuttx-ntfc/external/nuttx-testing --confpath=/github/workspace/sources/nuttx/boards/sim/sim/sim/configs/citest/config.yaml --jsonconf=/github/workspace/sources/nuttx/boards/sim/sim/sim/configs/citest/session.json
/github/workspace/sources/nuttx/../nuttx/boards/sim/sim/sim/configs/citest/run.sh: line 35: ntfc: command not found
+ ret=127
+ echo 127
+ artifacts=/github/workspace/buildartifacts/sim/citest//ntfc
+ mkdir -p /github/workspace/buildartifacts/sim/citest//ntfc
127
+ rm -f pytest.debug.log
+ mv result /github/workspace/buildartifacts/sim/citest//ntfc
mv: cannot stat 'result': No such file or directory
+ cd /github/workspace/sources/nuttx
+ exit 127
  [1/1] Normalize sim/citest
====================================================================================