Hello,
I have an A20-OLinuXino-Lime2 board and I'm attempting to use uart3. I've observed that uart3 is multiplexed on gpio1 pins 17 and 19. Following the instructions in the manual, I executed the command "~#olinuxino-overlay" to enable uart3. After rebooting, I confirmed that uart3 was successfully enabled. Additionally, when I run the command "ls -l /dev/ttyS3," it displays the correct output. However, when I performed a test by entering "echo 'some string' > /dev/ttyS3," I didn't observe any activity on the oscilloscope. I'm uncertain about the missing step or if there's something I overlooked. Any assistance you can provide would be greatly appreciated. Thank you for your help.
Did you first try with loopback tests? Connect pins 17 and 19 together and open terminal what you send you should receive...