How to use device tree overlays

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  8. Enabling I2C, SPI, UART, ADC, and PWM
  10. Enable a second UART

Enable a second UART

If you would like to use a UART that is not the main debug UART, the overlay GB-UART2-FLX4-AD2-AD3.dtbo will enable a second UART on pin AD2 and AD3. You can enable the second UART by editing the uEnv.txt

Make sure to uncomment the line enable_uboot_overlays=1 this allows overlays to load on boot: 

# enable u-boot overlays
enable_uboot_overlays=1

Then you can add the line GB-UART2-FLX4-AD2-AD3.dtbo to one of the pre-existing slots.