BeagleBone Black: how to activate UART 4 or 5 to enable RS-485 communication

Question

I want to enable RS-485 AND CANbus communications for my BBB using the comms cape 2.

I used to setup my Beaglebone black thru the /boot/uEnv.txt by overwriting with EEProm as follows:

###Overide capes with eeprom
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

And then I use ttyS4 for RS-485 comms.

Though it used to work on some BBBs, it's no longer the case on many others and many issues raise:

1. If I do that, the CANbus stops to work - probably messing the UART for the CANbus;
2. If I do not use CANbus, this settings does not seem to work anymore for the RS-485 itself - I guess something changed that depends on the linux version installed.

Long story short, I'd like to find a modern way to 1) setup RS-485 comms and 2) setup CANbus comm so that they work simultaneously.

And, possibly, how can I test RS-485 comms work, independent of my own software?

What I found on the Web:

The official cape comms doc here https://github.com/beagleboard/capes/tree/master/beaglebone/Comms tells how to setup things as follows:

For the RS485, you just need
config-pin p9.11 uart
config-pin p9.13 uart 
...and then use /dev/ttyS4

For the CAN, you just need
config-pin p9.24 can
config-pin p9.26 can

But in my case, setting config-pin p9.11 uart leads to the following error:

ERROR: open() for /sys/devices/platform/ocp/ocp:P9_11_pinmux/state failed, No such file or directory

This SO beaglebone black: no slots while enable uart tells how to setup UART5. They say to disable video, which I did. And to:

config-pin P8_37 uart
config-pin P8_38 uart

which works on my side, I mean no error was generated. And then I used ttS5 in my own software, but I cannot see anything on the RS-485.

At this time I am a bit puzzled: for example, should I overwrite EEPROM or not? Should I stick with the disabling of video, sound, etc. Why config-pin for UART4 doesn't work? Does UART 5 correspond to ttyS5? And how to make sure the ttySX I use really work with the RS-485 comm?

Thanks in advance.

APPENDIX: my current /boot/uEnv.txt

#Docs: http://elinux.org/Beagleboard:U-boot_partitioning_layout_2.0

uname_r=4.19.94-ti-r42
#uuid=
#dtb=

###U-Boot Overlays###
###Documentation: http://elinux.org/Beagleboard:BeagleBoneBlack_Debian#U$
###Master Enable
enable_uboot_overlays=1
###
###Overide capes with eeprom
#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
###
###Additional custom capes
#uboot_overlay_addr4=/lib/firmware/<file4>.dtbo
#uboot_overlay_addr5=/lib/firmware/<file5>.dtbo
#uboot_overlay_addr6=/lib/firmware/<file6>.dtbo
#uboot_overlay_addr7=/lib/firmware/<file7>.dtbo
###
###Custom Cape
#dtb_overlay=/lib/firmware/<file8>.dtbo
###
###Disable auto loading of virtual capes (emmc/video/wireless/adc)
#disable_uboot_overlay_emmc=1
disable_uboot_overlay_video=1
disable_uboot_overlay_audio=1
disable_uboot_overlay_wireless=1
#disable_uboot_overlay_adc=1
###
###PRUSS OPTIONS
###pru_rproc (4.14.x-ti kernel)
#uboot_overlay_pru=/lib/firmware/AM335X-PRU-RPROC-4-14-TI-00A0.dtbo
###pru_rproc (4.19.x-ti kernel)
uboot_overlay_pru=/lib/firmware/AM335X-PRU-RPROC-4-19-TI-00A0.dtbo
###pru_uio (4.14.x-ti, 4.19.x-ti & mainline/bone kernel)
#uboot_overlay_pru=/lib/firmware/AM335X-PRU-UIO-00A0.dtbo
###
###Cape Universal Enable
enable_uboot_cape_universal=1
###
###Debug: disable uboot autoload of Cape
#disable_uboot_overlay_addr0=1
#disable_uboot_overlay_addr1=1
#disable_uboot_overlay_addr2=1
#disable_uboot_overlay_addr3=1
###
###U-Boot fdt tweaks... (60000 = 384KB)
#uboot_fdt_buffer=0x60000
###U-Boot Overlays###

cmdline=coherent_pool=1M net.ifnames=0 lpj=1990656 rng_core.default_qual$

#In the event of edid real failures, uncomment this next line:
#cmdline=coherent_pool=1M net.ifnames=0 lpj=1990656 rng_core.default_qua$

##enable Generic eMMC Flasher:
##make sure, these tools are installed: dosfstools rsync
#cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh

Answer 1

Here is my /boot/uEnv.txt file:

#Docs: http://elinux.org/Beagleboard:U-boot_partitioning_layout_2.0

uname_r=4.19.94-ti-r71
#uuid=
#dtb=

###U-Boot Overlays###
###Documentation: http://elinux.org/Beagleboard:BeagleBoneBlack_Debian#U-Boot_Overlays
###Master Enable
enable_uboot_overlays=1
###
###Overide capes with eeprom
uboot_overlay_addr0=BONE-SPI1_0.dtbo
uboot_overlay_addr1=BONE-SPI0_0.dtbo
#uboot_overlay_addr2=<file2>.dtbo
#uboot_overlay_addr3=<file3>.dtbo

I did not apply the /lib/firmware sections in my uboot-overlays section(s).

This is ls -l /dev/spidev*

crw------- 1 root root 153, 0 Feb 10 00:39 /dev/spidev1.0
crw------- 1 root root 153, 1 Feb 10 00:39 /dev/spidev2.0

I think not being root might be an issue for me.

Anyway...the symlinks are used in source these days, I think, and there is also an up-to-date repo. from the BeagleBoard.org fellows/gals that help one to produce their.dts files into.dtb/o files. It is useful to me b/c I can then alter things or see what the people at beagleboard.org are doing w/ DT.

Answer 2

Finally, What I have done to fix the issue is:

• use ttyS4 for the RS-485;
• use can1 for CANbus communications.

The /boot/uEnv.txt is very simple then, simply do not set any UART, keep it as default. Here it is:

$ cat /boot/uEnv.txt

#Docs: http://elinux.org/Beagleboard:U-boot_partitioning_layout_2.0

uname_r=4.19.94-ti-r71
#uuid=
#dtb=

###U-Boot Overlays###
###Documentation: http://elinux.org/Beagleboard:BeagleBoneBlack_Debian#U-Boot_Overlays
###Master Enable
enable_uboot_overlays=1
###
###Overide capes with eeprom
#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


###Additional custom capes
#uboot_overlay_addr4=/lib/firmware/<file4>.dtbo
#uboot_overlay_addr5=/lib/firmware/<file5>.dtbo
#uboot_overlay_addr6=/lib/firmware/<file6>.dtbo
#uboot_overlay_addr7=/lib/firmware/<file7>.dtbo
###
###Custom Cape
#dtb_overlay=/lib/firmware/<file8>.dtbo
###
###Disable auto loading of virtual capes (emmc/video/wireless/adc)
#disable_uboot_overlay_emmc=1
disable_uboot_overlay_video=1
disable_uboot_overlay_audio=1
disable_uboot_overlay_wireless=1
disable_uboot_overlay_adc=1
###
###PRUSS OPTIONS
###pru_rproc (4.14.x-ti kernel)
#uboot_overlay_pru=/lib/firmware/AM335X-PRU-RPROC-4-14-TI-00A0.dtbo
###pru_rproc (4.19.x-ti kernel)
uboot_overlay_pru=/lib/firmware/AM335X-PRU-RPROC-4-19-TI-00A0.dtbo
###pru_uio (4.14.x-ti, 4.19.x-ti & mainline/bone kernel)
#uboot_overlay_pru=/lib/firmware/AM335X-PRU-UIO-00A0.dtbo
###
###Cape Universal Enable
enable_uboot_cape_universal=0
###
###Debug: disable uboot autoload of Cape
#disable_uboot_overlay_addr0=1
#disable_uboot_overlay_addr1=1
#disable_uboot_overlay_addr2=1
#disable_uboot_overlay_addr3=1
###
###U-Boot fdt tweaks... (60000 = 384KB)
#uboot_fdt_buffer=0x60000
###U-Boot Overlays###

cmdline=coherent_pool=1M net.ifnames=0 lpj=1990656 rng_core.default_quality=100 quiet

#In the event of edid real failures, uncomment this next line:
#cmdline=coherent_pool=1M net.ifnames=0 lpj=1990656 rng_core.default_quality=100 quiet video=HDMI-A-1:1024x768@60e

##enable Generic eMMC Flasher:
##make sure, these tools are installed: dosfstools rsync
#cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh