Enabling second UART in U-Boot

I am working on a project with SAMA5D3-xplained board with CortexA5 processor and embedded Linux. I would like to send and receive some data via UART during U-Boot is running and before a kernel is loaded to the RAM. I have no idea what I should do. Should I add the second UART to U-Boot device tree source file? Should I change something in a board configuration file? Do you have any ideas on what steps I should take to achieve my goal? Thank you in advance for any help. **EDIT:** I would like to use UART from U-Boot C code, not from U-Boot commands. I need to communicate with one of a peripheral device before the kernel is loaded to the RAM.