UART5 not working on Beaglebone Black

I am using a Beaglebone Black on a student project. In order to activate the UART5 port, I type in “echo BB-UART5 > /sys/devices/platform/bone_capemgr/slots” every time I power the board on. However, even though the port does seem to be activated, uart5 never works for any of the BBB’s I try (other UART ports on them work as well as usual) . What can cause such problems specifically with UART5? How can I fix it?

The IO pins used by UART5 are, by default, assigned to driving an LCD screen.
You will need to reconfigure the IO, so that LCD/video is disabled, and the pins are re-assigned as UART I/O pins.
You will need to modify the boot file and device tree.
Start searching about how to edit the /boot/uEnv.text file, and your different options for re-configuring the necessary pins.

— Graham

I tried uncommenting the lines in /boot/uEnv.txt about disabling HDMI, but it did not help. I also tried typing in optargs=capemgr.enable_partno=BB-UART1,BB-UART2,BB-UART3,BB-UART5 at the end of that file.
Then I was trying to type optargs=quiet capemgr.disable_partno=BB-BONELT-HDMI,BB-BONELT-HDMIN in order to explicitly disable the HDMI in the /boot/uEnv.txt, but it didn’t help either.

It appears that HDMI is not enabled there whatsoever since in the slots file I don’t have anything dedicated to it:
root@beaglebone:~# cat /sys/devices/platform/bone_capemgr/slots
0: PF---- -1
1: PF---- -1
2: PF---- -1
3: PF---- -1
4: P-O-L- 0 Override Board Name,00A0,Override Manuf,BB-I2C1
6: P-O-L- 1 Override Board Name,00A0,Override Manuf,BB-UART1
7: P-O-L- 2 Override Board Name,00A0,Override Manuf,BB-UART2
8: P-O-L- 3 Override Board Name,00A0,Override Manuf,BB-UART4
9: P-O-L- 4 Override Board Name,00A0,Override Manuf,BB-UART5
10: P-O-L- 5 Override Board Name,00A0,Override Manuf,BB-UART3

Are there any other possible sources of UART5 not working, aside from it interfering with HDMI? I tried several different boards and SD cards, but the port did not work on any of them.

Let’s start with a few clues.

What board and revision level are you using? (example: BeagleBone Black, Rev C.)

What OS, version, release date and kernel are you using?

What other changes, if any, have you made to the system software?

What hardware / I-O do you have plugged into the accessory connectors?

Do you have a serial debug cable plugged in? Is it giving you any boot errors or conflicts?