How to get the value of a camera register?

[JanGerber]

The application in our case is that we would like to read specific camera registers (I2C). Is this possible via Libargus?

[chakibdace]

Hi,

You can read a value of camera sensor register using i2c-tools package :

1. Check if the sensor is detected in the i2c bus

i2cdetect -r -y <I2C_BUS>

2. If you see that the slave address of your sensor appear in the i2c bus, you can get a register value by using the command line below

i2cset -f -y <I2C_BUS> <I2C_SENSOR_SLAVE_ADDR> <I2C_REG_ADDR> ; i2cget -f -y <I2C_BUS> <I2C_SENSOR_SLAVE_ADDR>

This should output the register value

If you want to use it directly from a C/C++ app you have the following code as a reference

#include <fcntl.h>
#include <linux/i2c-dev.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdint.h>

int main() {
    const char* i2cDevice = "/dev/i2c-0";  // Specify the correct I2C device file
    int address = 0x50;  // Replace with the sensor's actual I2C address
    int registerAddress = 0x10;  // Replace with the register address you want to read
    
    // Open the I2C device
    int file = open(i2cDevice, O_RDWR);
    if (file < 0) {
        perror("Failed to open the I2C device.");
        return 1;
    }
    
    // Set the I2C slave address
    if (ioctl(file, I2C_SLAVE, address) < 0) {
        perror("Failed to set I2C slave address.");
        close(file);
        return 1;
    }
    
    // Send the register address to read from
    if (write(file, &registerAddress, sizeof(registerAddress)) != sizeof(registerAddress)) {
        perror("Failed to write register address.");
        close(file);
        return 1;
    }
    
    // Read the register value
    uint8_t registerValue;
    if (read(file, &registerValue, sizeof(registerValue)) != sizeof(registerValue)) {
        perror("Failed to read register value.");
        close(file);
        return 1;
    }
    
    // Print the register value
    printf("Register 0x%02X value: 0x%02X\n", registerAddress, registerValue);
    
    // Close the I2C device
    close(file);
    
    return 0;
}

And btw LibArgus is an API to capture camera streaming from a camera module that output RAW data, this API use Jetson’s ISP for debayering and ISP’s stuff so the output will be in NV12 format.

I also recommand to implement read_i2c_reg function in your sensor driver, this latter can be as the one below

/*
 * ds3231_read_reg() - read a register value from the DS3231 RTC
 *
 * @dev: pointer to the device structure
 * @addr: the register address to read from
 * @val: pointer to store the value read from the register
 *
 * Return: 0 on success, negative error code on failure
 */
static int ds3231_read_reg(struct device *dev, u16 addr, u32 *val)
{
    struct ds3231 *priv = dev_get_drvdata(dev);
    int err;

    /* Read the value from the register at the specified address */
    err = regmap_read(priv->regmap, addr, val);
    dev_info(dev, "%s:i2c read data, 0x%x = 0x%x", __func__, addr, *val);

    if (err)
        dev_err(dev, "%s:i2c read failed, 0x%x\n", __func__, addr);

    /* Delay before the next I2C command to avoid overloading the bus */
    usleep_range(100, 110);

    return err;
}

You can also have many references in nvidia image sensors drivers from public sources

See the path :

/sources/drivers/media/i2c/