Can I enable I2C before first boot?

Question

I want to enable the I2C interface, but without having to boot, login, and the whole sudo raspi-config.

I tried editing /boot/config.txt right after sudo dd the image to the disk, still in my main computer, and uncommented the dtparam=i2c_arm=on line.

Now, everytime I reboot, it's like the interface is disabled. The line is still uncommented, and i2c-dev is the only thing in the /etc/modules file. Now everytime I reboot, I have to do sudo raspi-config all over again to make it work.

Is it something about permissions? I don't know where to look for problems here.

Edit as requested:

I wrote aversion of the INA219 library in C++, INA uses i2c.

This is how you can try it: git clone http://github.com/regisin/pi_ina219cpp make ./build/profiler

The library works fine if I use the sudo raspi-config (not even trying the manual part), and ev en when rebooting it continues to work.

However, when I tried to edit the /boot/config.txt file, it only works if I do a sudo modprobe i2c-dev manually, after the boot.

Edit 2:

If you read the previous section you noticed I used modprobe. I looked into the /usr/bin/raspi-config file, and noticed that the i2c function does a few commands:

1 - uncomment or add dtparam=i2c_arm=on line to /boot/config.txt 2 - insert i2c-dev to the /etc/modules 3 - dtparam i2c_arm=on 4 - modprobe i2c-dev

What puzzles me is that after editing /boot/config.txt directly in the sd card from another machine, raspi-config does not work as expected. It's like some configuration is resetting at boot time. I guess I could work around this by doing modprobe when booting, but it does not sound like that's the intended behavior.

Answer 1

The information supplied seems contradictory.

You need to do two things to enable the I2C bus.

1. Edit /boot/config.txt and enable the device tree entry.
2. Add the line i2c-dev to /etc/modules.

I suspect you are not adding i2c-dev to /etc/modules prior to the first boot.