V4L2 Camera Driver Development Custom Controls

Autonomous Machines Jetson & Embedded Systems Jetson Nano
1

Hello. I am new to Jetson Nano and V4L2 Driver Development in general. I have written a working V4L2 camera driver for another Linux platform. While porting to Jetson Nano I came up with 2 questions I have not found an answer for in the examples. If I was missing something, please let me know :)
While porting I was using your guide on how to implement the driver with tegracam. So I am using 2.0. Since I am using monochrome sensor I am not using your ISP with gstreamer, instead I use v4l2 C-API in my own C++ application I am writing. I mostly used the v4l2-cuda example for that.

I can set exposure time correctly using v4l2-ctl -c exposure=90 from the command line. But when I try to set it in my C Application it gives “Invalid Argument”.

bool v4l2_ctrl_set(int fd, uint32_t id, int val)
{
    struct v4l2_control ctrl;
    CLEAR(ctrl);

    ctrl.id = id;
    ctrl.value = val;
    if (xioctl(fd, VIDIOC_S_CTRL, &ctrl) == -1) {
        std::cout << "Failed to set ctrl with id " 
                  << id << " to value " << val
                  << "\nerror (" << errno << "): " << strerror(errno) << std::endl;

       	return false;
    }
    
    return true;
}

  1. How do I set V4l2-ctrls with C-API using the tegracam implementation in my driver?

  2. How should I implement custom V4L2 controls using tegracam. For example I want to set top/left readout offset values for my camera. Should I change the tegracam files, or should I add another custom control handler from my driver? How to make it compatible with tegracam 2.0 driver development?

Sorry for my basic questions.

Best regards,
jb

3

hello busch.johannes,

assume you have check Sensor Software Driver Programming Guide for sensor driver implementation.

you may check below kernel sources for available TEGRA_CAMERA_CID_* controls,
let’s taking preferred stride controls as an example,
$L4T_Sources/r32.4.3/Linux_for_Tegra/source/public/kernel/nvidia/include/media/tegra-v4l2-camera.h

#define TEGRA_CAMERA_CID_BASE   (V4L2_CTRL_CLASS_CAMERA | 0x2000)
...
#define TEGRA_CAMERA_CID_VI_PREFERRED_STRIDE (TEGRA_CAMERA_CID_BASE+110)

you should also refer to VI driver, which define the CID control property and also parse the control settings,
$L4T_Sources/r32.4.3/Linux_for_Tegra/source/public/kernel/nvidia/drivers/media/platform/tegra/camera/vi/channel.c

static const struct v4l2_ctrl_config common_custom_ctrls[] = {
...
        {
                .ops = &channel_ctrl_ops,
                .id = TEGRA_CAMERA_CID_VI_PREFERRED_STRIDE,
                ...

int tegra_channel_s_ctrl(struct v4l2_ctrl *ctrl)

        switch (ctrl->id) {
        ...
        case TEGRA_CAMERA_CID_VI_PREFERRED_STRIDE:
                chan->preferred_stride = ctrl->val;
                tegra_channel_update_format(...)

you may enable v4l2-ctl to display all available information, to check whether you’d implement that correctly,

$ v4l2-ctl --all
...
               preferred_stride 0x009a206e (int)    : min=0 max=65535 step=1 default=0 value=0

then, you’ll able to enable --set-ctrl flags to assign your property settings into VI drivers.
for example, $ v4l2-ctl -d /dev/video0 ... --set-ctrl preferred_stride=256 ...

moreover,
if you would like to extend your customize CID controls,
please adding specific CID flags to tegra-v4l2-camera.h,
you should also have implementation in the VI drivers, channel.c.
thanks

4

Thanks for your fast response. I’ll try that next week.
Can you also help me with my 1st question? For Exposure setting the v4l2-ctl command does work but calling from my userspace application the above code for exposure gives me invalid argument. Which header files do I have to include to set exposure from c++ user space application?

Am I doing sth wrong?

Best regards,
Jb

5

hello busch.johannes,

please also refer to Property-Value Pairs supported for version 2.0 sensor drivers.
you should enable TEGRA_CAMERA_CID_EXPOSURE controls to set your sensor exposure times.
thanks

7

I could figure out how to achieve what I wanted by myself, so here is what I needed to do to set Sensor Ctrl Settings from my C++ userspace application:

struct v4l2_ext_controls ctrls;
struct v4l2_ext_control ctrl;
CLEAR(ctrl);
CLEAR(ctrls);
ctrls.controls = &ctrl;
ctrls.count = 1;
ctrls.which = V4L2_CTRL_WHICH_CUR_VAL;

ctrl.id = TEGRA_CAMERA_CID_EXPOSURE;
ctrl.value = ;
if (xioctl(fd, VIDIOC_S_EXT_CTRLS, &ctrls) == -1) {
     fprintf(stderr, "Error VIDIOC_S_EXT_CTRLS %s\n",strerror(errno));
 }

Thank you anyway for your help!

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