configure pi as a usb gadget, add vivid driver to the image, build and run code

Question

Need to configure RPi as a USB UVC (video camera gadget). As far as I understand here is how it can be done. Then I need to test this application. Instructions on how to do it located here.

Questions

1. How can I add Virtual Video Driver to the Raspberry PI image?
2. How can I cross compile this code on my host, for it later to be copied to the RPi. I need this option just in case I would not be able to compile it directly on RPi. Just a precaution.

Any help is appreciated.

Answer 1

I assume this is with a Pi Zero (or old Pi model A/A+). OTG won't work on a Pi 3 or most other models.

I'll answer your second question first because it'll come in handy for question 1).

For 2), once you are set up to cross-compile the kernel--having retrieved the tools and set up your PATH--you'll be ready to compile uvc-gadget similarly:

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf-

uvc-gadget is a small application so I actually find it more convenient to to make changes and build on the Pi Zero. Unfortunately, the same is not true for the kernel.

The latest Raspbian 9 Stretch defaults to a gcc 6 toolchain/libc while the tools repo is apparently still gcc 4.9. You may have to revert to Raspbian 8 Jessie to avoid getting a segfault even on a hello world application, or find an updated toolchain.

For 1), you'll need to configure the kernel for CONFIG_VIDEO_VIVID and recompile. After you have gotten the hang of building the kernel + modules and uploading it to your Pi,

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig

Device Drivers -> Multimedia Support -> Media test drivers -> Virtual Video Test Driver (set to M)

then recompile the kernel + modules and it should generate a vivid.ko file. I have only confirmed that it compiles, not necessarily loads or runs properly. To date my testing with uvc-gadget on a Pi zero has relied on synthetic image data (-d).