I'm trying to use the I2C bus using the SDA1 (GPIO 2 / P0.14) and SCL1 (GPIO 3 / P0.15) pins, but I haven't yet figured out how to "activate" these pins for I2C usage. It looks like everything defaults to the AIN0_A5/SCL (GPIO18 / P0.02) and AIN7_A4/SDA (GPIO 20 / P0.31) pins.
The SDA1 and SCL1 pins are found in the EAGLE files for the Arduino Nano 33 BLE:
As an example, I made a custom PCB with the Nina B306 and an LSM6DS3. The LSM6DS3's SDA and SCL pins are connected to the SDA1 and SCL1 pins. I've successfully bootloaded the Nina B306 with the Arduino bootloader, and can upload sketches to it no problem. However, when I run any of Arduino's example sketches for the LSM6DS3, the IMU cannot be detected. I suspect it's looking for the device on the "default" I2C lines using A4 and A5.
Any guidance on how to switch these over to SDA1 and SCL1? My searching has come up dry, and I'm beginning to suspect I'm just not using the correct search terms.