uvc-gadget

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I tried to use frambuffer instead of /dev/video0, but the webcam application show nothing. Here is what I did:

# ./gadget-framebuffer.sh 
INFO: --- Gadget framebuffer ---
INFO: Framebuffer width:  640
INFO: Framebuffer height: 480
INFO: Configfs path: /sys/kernel/config
INFO: Gadget config path: /sys/kernel/config/usb_gadget/fb_gadget
INFO: Initialize configs and functions
INFO: Enabling gadget
INFO: End

# ./uvc-gadget -u /dev/video1 -f /dev/fb0
[1] 404
root@raspberrypi:/home/pi/tuyenld/uvc-webcam# CONFIGFS: Initial path: /sys/kernel/config/usb_gadget
CONFIGFS: UVC: format: 0, frame: 0, resolution: 640x480, frame_interval: 1000000,  bitrate: [24576000, 49152000]
CONFIGFS: STREAMING maxburst:  0
CONFIGFS: STREAMING maxpacket: 2048
CONFIGFS: STREAMING interval:  1
SETTINGS: Number of buffers requested: 2
SETTINGS: Show FPS: DISABLED
SETTINGS: GPIO pin for streaming status: not set
SETTINGS: Onboard led0 used for streaming status: DISABLED
SETTINGS: Blink on startup: 0 times
SETTINGS: UVC device name: /dev/video1
SETTINGS: FB device name: /dev/fb0
SETTINGS: Framerate for frame buffer: 25
DEVICE_UVC: Opening /dev/video1 device
DEVICE_UVC: Device is 20980000.usb on bus gadget
FB: Opening /dev/fb0 device
FB: Resolution: 640x480
FB: Bits per pixel: 32
FB: Line length: 2560
FB: Memory size: 1228800
UVC: Streaming control: action: INIT
FRAME: format: 0, frame: 0, resolution: 640x480, frame_interval: 1000000,  bitrate: [24576000, 49152000]
DUMP: uvc_streaming_control: format: 0, frame: 0, frame interval: 1000000
UVC: Streaming control: action: INIT
FRAME: format: 0, frame: 0, resolution: 640x480, frame_interval: 1000000,  bitrate: [24576000, 49152000]
DUMP: uvc_streaming_control: format: 0, frame: 0, frame interval: 1000000
PROCESSING LOOP: FB -> UVC
DEVICE_UVC: UVC_EVENT_CONNECT
UVC: INPUT_TERMINAL - GET_INFO - UVC_CT_AE_MODE_CONTROL - DISABLED
UVC: PROCESSING_UNIT - GET_INFO - UVC_PU_BRIGHTNESS_CONTROL - DISABLED
UVC: Streaming request CS: PROBE, REQ: GET_DEF
UVC: Streaming control: action: GET MIN
FRAME: format: 0, frame: 0, resolution: 640x480, frame_interval: 1000000,  bitrate: [24576000, 49152000]
DUMP: uvc_streaming_control: format: 0, frame: 0, frame interval: 1000000
UVC: Streaming request CS: PROBE, REQ: SET_CUR
UVC: Control PROBE, length: 26
UVC: Streaming control: action: SET, format: 0, frame: 0
FRAME: format: 0, frame: 0, resolution: 640x480, frame_interval: 1000000,  bitrate: [24576000, 49152000]
DUMP: uvc_streaming_control: format: 0, frame: 0, frame interval: 1000000
UVC: Streaming request CS: PROBE, REQ: GET_CUR
UVC: PROCESSING_UNIT - GET_DEF - UVC_PU_BRIGHTNESS_CONTROL - DISABLED
UVC: PROCESSING_UNIT - GET_DEF - UVC_PU_BRIGHTNESS_CONTROL - DISABLED
UVC: PROCESSING_UNIT - GET_DEF - UVC_PU_BRIGHTNESS_CONTROL - DISABLED
UVC: PROCESSING_UNIT - GET_DEF - UVC_PU_BRIGHTNESS_CONTROL - DISABLED

I also tried to force HDMI output mode, but no luck.

# cat /boot/config.txt
[...]
hdmi_force_hotplug=1
hdmi_drive=2

Camera preview mode on RasPi is using GPU, so I think it is easy to overlay text or image with Camera video output. Could you give me more detail how to use framebuffer?

If you set the framebuffer as an input device, then you must set uvc gadget as an output device.

v4l2-ctl --list-device 20980000.usb (gadget): /dev/video0

uvc-gadget -f /dev/fb0 -u /dev/video0

In your command you use /dev/video1 which is probably a camera module.