i2c.rst

I2C via Greybus

After running gbridge, if the board in use exposes I2C via Greybus, then the Linux kernel will create /dev/i2c-N entries for you.

Just to make sure that we're interacting with the Greybus I2C device, run the following (reading and writing to random I2C devices can sometimes have negative consequences).

ls -la /sys/bus/i2c/devices/* | grep "greybus"
lrwxrwxrwx 1 root root 0 Aug 15 11:24 /sys/bus/i2c/devices/i2c-8 -> ../../../devices/virtual/gb_nl/gn_nl/greybus1/1-2/1-2.2/1-2.2.2/gbphy2/i2c-8

In this case, we will read values a number of sensors on the cc1352r_sensortag.

First, read the ID registers (at the i2c register address 0x7e) of the opt3001 sensor (at i2c bus address 0x44) as shown below:

i2cget -y 8 0x44 0x7e w
0x4954

Next, read the ID registers (at the i2c register address 0xfc) of the hdc2080 sensor (at i2c bus address 0x41) as shown below:

i2cget -y 8 0x41 0xfc w
0x5449

Lastly, we are going to probe the Linux kernel driver for the opt3001 and use the Linux IIO subsystem to read ambient light values.

echo opt3001 0x44 | sudo tee /sys/bus/i2c/devices/i2c-8/new_device
cd /sys/bus/iio/devices/iio:device0
cat in_illuminance_input
163

What is very interesting about the last example is that we are using the local Linux driver to interact with the remote I2C PHY. In other words, our microcontroller does not even require a specific driver for the sensor and we can maintain the driver code in the Linux kernel!