Enabling UART 1 and 2 on Beaglebone Black with Yocto Kirkstone

General Discussion
10

Don’t start laughing, its easier to mount the SD card on your metal box and edit extlinux.conf. It does not mount the entire sd card.
I just tried to load the overlays and they are not loading.

U-Boot SPL 2023.04-ti-g2a13324ec63c (Jan 17 2025 - 00:39:49 +0000)
Trying to boot from MMC1


U-Boot 2023.04-ti-g2a13324ec63c (Jan 17 2025 - 00:39:49 +0000)

CPU  : AM335X-GP rev 2.1
Model: TI AM335x BeagleBone Black
DRAM:  512 MiB
Core:  160 devices, 18 uclasses, devicetree: separate
WDT:   Started wdt@44e35000 with servicing every 1000ms (60s timeout)
NAND:  0 MiB
MMC:   OMAP SD/MMC: 0, OMAP SD/MMC: 1
Loading Environment from FAT... Unable to read "uboot.env" from mmc0:1... 
<ethaddr> not set. Validating first E-fuse MAC
Net:   eth2: ethernet@4a100000, eth3: usb_ether
Hit any key to stop autoboot:  0 
switch to partitions #0, OK
mmc0 is current device
Scanning mmc 0:1...
Found /extlinux/extlinux.conf
Retrieving file: /extlinux/extlinux.conf
1:	Arago
Retrieving file: /extlinux/../zImage
append: root=PARTUUID=81fdff7f-02 rootwait rw earlycon console=ttyO0,115200n8,115200
Retrieving file: /extlinux/../am335x-boneblack.dtb
Retrieving file: /boot/BB-UART4-00A0.dtbo
Failed loading overlay /boot/BB-UART4-00A0.dtbo
Retrieving file: /boot/BB-UART1-00A0.dtbo
Failed loading overlay /boot/BB-UART1-00A0.dtbo
Retrieving file: /boot/BB-UART2-00A0.dtbo
Failed loading overlay /boot/BB-UART2-00A0.dtbo
Kernel image @ 0x82000000 [ 0x000000 - 0xc04200 ]
## Flattened Device Tree blob at 88000000
   Booting using the fdt blob at 0x88000000
Working FDT set to 88000000
   Loading Device Tree to 8ffe4000, end 8ffff305 ... OK
Working FDT set to 8ffe4000



# Generic Distro Configuration file generated by OpenEmbedded
LABEL Arago
	KERNEL ../zImage
	FDTDIR ../
	APPEND root=PARTUUID=${uuid} rootwait rw earlycon console=${console},${baudrate}
	fdtoverlays /boot/BB-UART4-00A0.dtbo /boot/BB-UART1-00A0.dtbo /boot/BB-UART2-00A0.dtbo

Not sure why its not loading.

It does not work with the other variant FDTOVERLAYS either but it is retrieving them. If you cannot get it to work just toss it and use another board vendor. For some reason Ti has omitted the overlays from the docs or I am too old and stupid to find them.

UPDATE: Blame me for the overlay loading issue. Here is the fix and how to diagnose the problem

You can fiddle around with the path in u-boot:

=> printenv bootcmd_mmc0
bootcmd_mmc0=devnum=0; run mmc_boot
=> printenv bootcmd
bootcmd=run findfdt; run init_console; run finduuid; run distro_bootcmd
=> load mmc 0:1 ${fdtoverlay_addr_r} /boot/BB-UART1-00A0.dtbo        
Failed to load '/boot/BB-UART1-00A0.dtbo'
=> load mmc 0:1 ${fdtoverlay_addr_r} ../BB-UART1-00A0.dtbo   
1017 bytes read in 3 ms (331.1 KiB/s)
=> 


U-Boot SPL 2023.04-ti-g2a13324ec63c (Jan 17 2025 - 00:39:49 +0000)
Trying to boot from MMC1


U-Boot 2023.04-ti-g2a13324ec63c (Jan 17 2025 - 00:39:49 +0000)

CPU  : AM335X-GP rev 2.1
Model: TI AM335x BeagleBone Black
DRAM:  512 MiB
Core:  160 devices, 18 uclasses, devicetree: separate
WDT:   Started wdt@44e35000 with servicing every 1000ms (60s timeout)
NAND:  0 MiB
MMC:   OMAP SD/MMC: 0, OMAP SD/MMC: 1
Loading Environment from FAT... Unable to read "uboot.env" from mmc0:1... 
<ethaddr> not set. Validating first E-fuse MAC
Net:   eth2: ethernet@4a100000, eth3: usb_ether
Hit any key to stop autoboot:  0 
switch to partitions #0, OK
mmc0 is current device
Scanning mmc 0:1...
Found /extlinux/extlinux.conf
Retrieving file: /extlinux/extlinux.conf
1:	Arago
Retrieving file: /extlinux/../zImage
append: root=PARTUUID=81fdff7f-02 rootwait rw earlycon console=ttyO0,115200n8,115200
Retrieving file: /extlinux/../am335x-boneblack.dtb
Retrieving file: /extlinux/../BB-UART4-00A0.dtbo
Retrieving file: /extlinux/../BB-UART1-00A0.dtbo
Retrieving file: /extlinux/../BB-UART2-00A0.dtbo
Kernel image @ 0x82000000 [ 0x000000 - 0xc04200 ]
## Flattened Device Tree blob at 88000000
   Booting using the fdt blob at 0x88000000
Working FDT set to 88000000
   Loading Device Tree to 8ffe2000, end 8fffffff ... OK
Working FDT set to 8ffe2000


root@beaglebone:~# ls /dev/ttyS* /dev/ttyO* /dev/ttyAMA* /dev/ttyUSB* 2>/dev/null
 /dev/ttyS0   /dev/ttyS1   /dev/ttyS2   /dev/ttyS3   /dev/ttyS4   /dev/ttyS5
root@beaglebone:~# cat /sys/class/tty/ttyS*/dev
4:64
4:65
4:66
4:67
4:68
4:69
root@beaglebone:~# echo "Hello UART" > /dev/ttyS1
root@beaglebone:~#

Working extlinux.conf

# Generic Distro Configuration file generated by OpenEmbedded
LABEL Arago
	KERNEL ../zImage
	FDTDIR ../
	APPEND root=PARTUUID=${uuid} rootwait rw earlycon console=${console},${baudrate}
	fdtoverlays ../BB-UART4-00A0.dtbo ../BB-UART1-00A0.dtbo ../BB-UART2-00A0.dtbo
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