I'm attempting to enable all the UARTs on the Beaglebone Black (UART 1-5). I am running debian 9.3 and using the BeagleBone Black rev C. I am attempting to enable all UARTs by modifying the uEnv.txt file (I have been putting this file in the root directory and the /boot directory, with the same results either way).
This is my uEnv.txt file:
uname_r=4.9.82-ti-r102 enable_uboot_overlays=1 uboot_overlay_addr0=/lib/firmware/BB-UART1-00A0.dtbo uboot_overlay_addr1=/lib/firmware/BB-UART2-00A0.dtbo uboot_overlay_addr2=/lib/firmware/BB-UART4-00A0.dtbo uboot_overlay_addr3=/lib/firmware/BB-UART5-00A0.dtbo uboot_overlay_addr4=/lib/firmware/BB-UART3-00A0.dtbo cmdline=coherent_pool=1M net.ifnames=0 quiet cape_universal=enable cape_disable=bone_capemgr.disable_partno=BB-BONELT-HDMI,BB-BONELT-HDMINN cape_enable=bone_capemgr.enable_partno=BB-UART1,BB-UART2,BB-UART3,BB-UART4,BB-UART5
I have tried this file on several BeagleBone Blacks. On two of them, this file works and does enable all 5 UART devices (all /dev/ttyO1-5 are shown). However, on some other BeagleBone Blacks, only UART 1-4 gets enabled (evidenced by /dev/ttyO1-O4 showing up and being usable, but not /dev/ttyO5); UART 5 does not get enabled.
Nothing else is different in the OS Images in my trials. I have been using a fresh debian 9.3 on the SD card with the only modification being this uEnv.txt. In fact, I have even taken the same SD card from one working BeagleBone, put it in one that won't enable all 5 UARTs, and booted with the same results; UART 5 will not enable. I suspect it may be a bootlaoder issue since it seems specific to the very specific BeagleBone black I am using, and not the OS.
Does anyone have any ideas on why this file will work on one beaglebone and not on another? Unfortunately, due to the application I am developing, this can't be solved by just using the beaglebone(s) that work; I need to find a reliable solution.
As I said previously, I suspect it may be a bootloader issue however I'm quite unsure. My next steps I'm thinking about involve updating the bootloader, or going to a different Debian version.
Thank you in advance for the help!
Edit: I think on further inspection this may be an issue with the HDMI. I tried to disable the HDMI in the uEnv.txt file, however when checking /sys/devices/platform/bone_capemgr/slots there doesn't appear to be a line disabling the HDMI. This would make sense since UART 5 is tied up with the HDMI interface if it is not disabled if I'm not mistaken. However, I'm not quite sure how to fix this.