mjhjmtu

I am trying to get an embedded linux build using yocto to work. I'm very close, but I'm having trouble with the boot. I have 2 root file systems. One is the main and the other is to be used during firmware upgrades. However, I can't get the system to boot off anything but the first rootfs.

Here is my partition layout:

Disk /dev/mmcblk1: 3825 MB, 3825205248 bytes
4 heads, 16 sectors/track, 116736 cylinders
Units = cylinders of 64 * 512 = 32768 bytes

 Device Boot Start End Blocks Id System
/dev/mmcblk1p1 * 33 6432 204800 c Win95 FAT32 (LBA)
/dev/mmcblk1p2 6433 19232 409600 83 Linux
/dev/mmcblk1p3 19233 32032 409600 83 Linux
/dev/mmcblk1p4 32033 97568 2097152 5 Extended
/dev/mmcblk1p5 32065 43264 358400 83 Linux
/dev/mmcblk1p6 43297 97568 1736704 83 Linux

/dev/mmcblk1p2 and /dev/mmcblk1p3 are the root file systems.

Current when I boot the machine it boots off /dev/mmcblk1p2, despite having mmcroot configured as /dev/mmcblk1p3 in uEnv.txt. Here is my uEnv:

bootdir=
bootfile=zImage
fdtfile=am335x-boneblack.dtb
loadaddr=0x80007fc0
fdtaddr=0x80F80000
console=ttyO0,115200
mmcroot=/dev/mmcblk1p3
mmcrootfstype=ext4
loadfdt=fatload mmc 1:1 $fdtaddr $fdtfile
loaduimage=fatload mmc 1:1 $loadaddr $bootfile
mmc_args=setenv bootargs console=$console $optargs root=$mmcroot rootfstype=$mmcrootfstype
uenvcmd=mmc rescan; run loaduimage; run loadfdt; run fdtboot
fdtboot=run mmc_args; run mmcargs; bootz $loadaddr - $fdtaddr

Also, here are the results of a boot:

U-Boot SPL 2017.09 (Feb 15 2018 - 07:11:54)
Trying to boot from MMC2
reading u-boot.img
reading u-boot.img


U-Boot 2017.09 (Feb 15 2018 - 07:11:54 -0500)

CPU : AM335X-GP rev 2.1
I2C: ready
DRAM: 512 MiB
No match for driver 'omap_hsmmc'
No match for driver 'omap_hsmmc'
Some drivers were not found
MMC: OMAP SD/MMC: 0, OMAP SD/MMC: 1
Net: cpsw, usb_ether
Press SPACE to abort autoboot in 2 seconds
Card did not respond to voltage select!
mmc_init: -95, time 12
Card did not respond to voltage select!
mmc_init: -95, time 12
Card did not respond to voltage select!
mmc_init: -95, time 13
Card did not respond to voltage select!
mmc_init: -95, time 13
Card did not respond to voltage select!
mmc_init: -95, time 12
switch to partitions #0, OK
mmc1(part 0) is current device
Scanning mmc 1:1...
reading /am335x-boneblack.dtb
36168 bytes read in 9 ms (3.8 MiB/s)
switch to partitions #0, OK
mmc1(part 0) is current device
SD/MMC found on device 1
5768968 bytes read in 380 ms (14.5 MiB/s)
36168 bytes read in 22 ms (1.6 MiB/s)
## Flattened Device Tree blob at 88000000
 Booting using the fdt blob at 0x88000000
 Loading Device Tree to 8fff4000, end 8ffffd47 ... OK

Starting kernel ...

Booting Linux on physical CPU 0x0
Linux version 4.12.12-yocto-standard (oe-user@oe-host) (gcc version 7.3.0 (GCC) ) #1 PREEMPT Thu Feb 15 07:09:00 EST 2018
CPU: ARMv7 Processor [413fc082] revision 2 (ARMv7), cr=10c5387d
CPU: PIPT / VIPT nonaliasing data cache, VIPT aliasing instruction cache
OF: fdt: Machine model: TI AM335x BeagleBone Black
Memory policy: Data cache writeback
cma: Reserved 16 MiB at 0x9e800000
CPU: All CPU(s) started in SVC mode.
AM335X ES2.1 (sgx neon)
Built 1 zonelists in Zone order, mobility grouping on. Total pages: 129666
Kernel command line: console=ttyO0,115200n8 root=PARTUUID=b804e92a-02 rw rootfstype=ext4 rootwait
PID hash table entries: 2048 (order: 1, 8192 bytes)
Dentry cache hash table entries: 65536 (order: 6, 262144 bytes)
Inode-cache hash table entries: 32768 (order: 5, 131072 bytes)
Memory: 486888K/523264K available (8192K kernel code, 778K rwdata, 2600K rodata, 1024K init, 595K bss, 19992K reserved, 16384K cma-reserved, 0K highmem)
Virtual kernel memory layout:
 vector : 0xffff0000 - 0xffff1000 ( 4 kB)
 fixmap : 0xffc00000 - 0xfff00000 (3072 kB)
 vmalloc : 0xe0000000 - 0xff800000 ( 504 MB)
 lowmem : 0xc0000000 - 0xdff00000 ( 511 MB)
 pkmap : 0xbfe00000 - 0xc0000000 ( 2 MB)
 modules : 0xbf000000 - 0xbfe00000 ( 14 MB)
 .text : 0xc0008000 - 0xc0900000 (9184 kB)
 .init : 0xc0d00000 - 0xc0e00000 (1024 kB)
 .data : 0xc0e00000 - 0xc0ec29ec ( 779 kB)
 .bss : 0xc0ecc6c4 - 0xc0f6134c ( 596 kB)
SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
ftrace: allocating 30390 entries in 90 pages
Preemptible hierarchical RCU implementation.
NR_IRQS:16 nr_irqs:16 16
IRQ: Found an INTC at 0xfa200000 (revision 5.0) with 128 interrupts
OMAP clockevent source: timer2 at 24000000 Hz
sched_clock: 32 bits at 24MHz, resolution 41ns, wraps every 89478484971ns
clocksource: timer1: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 79635851949 ns
OMAP clocksource: timer1 at 24000000 Hz
clocksource_probe: no matching clocksources found
Console: colour dummy device 80x30
Calibrating delay loop... 996.14 BogoMIPS (lpj=4980736)
pid_max: default: 32768 minimum: 301
Security Framework initialized
Mount-cache hash table entries: 1024 (order: 0, 4096 bytes)
Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes)
CPU: Testing write buffer coherency: ok
Setting up static identity map for 0x80100000 - 0x80100060
devtmpfs: initialized
VFP support v0.3: implementor 41 architecture 3 part 30 variant c rev 3
clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns
futex hash table entries: 256 (order: -1, 3072 bytes)
xor: measuring software checksum speed
 arm4regs : 1201.600 MB/sec
 8regs : 893.200 MB/sec
 32regs : 1156.400 MB/sec
xor: using function: arm4regs (1201.600 MB/sec)
pinctrl core: initialized pinctrl subsystem
NET: Registered protocol family 16
DMA: preallocated 256 KiB pool for atomic coherent allocations
omap_hwmod: debugss: _wait_target_disable failed
cpuidle: using governor ladder
cpuidle: using governor menu
OMAP GPIO hardware version 0.1
hw-breakpoint: debug architecture 0x4 unsupported.
raid6: int32x1 gen() 209 MB/s
raid6: int32x1 xor() 143 MB/s
raid6: int32x2 gen() 226 MB/s
raid6: int32x2 xor() 162 MB/s
raid6: int32x4 gen() 190 MB/s
raid6: int32x4 xor() 133 MB/s
raid6: int32x8 gen() 175 MB/s
raid6: int32x8 xor() 118 MB/s
raid6: using algorithm int32x2 gen() 226 MB/s
raid6: .... xor() 162 MB/s, rmw enabled
raid6: using intx1 recovery algorithm
edma 49000000.edma: TI EDMA DMA engine driver
SCSI subsystem initialized
usbcore: registered new interface driver usbfs
usbcore: registered new interface driver hub
usbcore: registered new device driver usb
omap_i2c 44e0b000.i2c: could not find pctldev for node /ocp/l4_wkup@44c00000/scm@210000/pinmux@800/pinmux_i2c0_pins, deferring probe
omap_i2c 4802a000.i2c: could not find pctldev for node /ocp/l4_wkup@44c00000/scm@210000/pinmux@800/pinmux_i2c1_pins, deferring probe
omap_i2c 4819c000.i2c: could not find pctldev for node /ocp/l4_wkup@44c00000/scm@210000/pinmux@800/pinmux_i2c2_pins, deferring probe
clocksource: Switched to clocksource timer1
NET: Registered protocol family 2
TCP established hash table entries: 4096 (order: 2, 16384 bytes)
TCP bind hash table entries: 4096 (order: 2, 16384 bytes)
TCP: Hash tables configured (established 4096 bind 4096)
UDP hash table entries: 256 (order: 0, 4096 bytes)
UDP-Lite hash table entries: 256 (order: 0, 4096 bytes)
NET: Registered protocol family 1
RPC: Registered named UNIX socket transport module.
RPC: Registered udp transport module.
RPC: Registered tcp transport module.
RPC: Registered tcp NFSv4.1 backchannel transport module.
hw perfevents: no interrupt-affinity property for /pmu, guessing.
hw perfevents: enabled with armv7_cortex_a8 PMU driver, 5 counters available
workingset: timestamp_bits=14 max_order=17 bucket_order=3
NFS: Registering the id_resolver key type
Key type id_resolver registered
Key type id_legacy registered
Block layer SCSI generic (bsg) driver version 0.4 loaded (major 251)
io scheduler noop registered
io scheduler deadline registered
io scheduler cfq registered (default)
io scheduler mq-deadline registered
io scheduler kyber registered
pinctrl-single 44e10800.pinmux: 142 pins at pa f9e10800 size 568
omap_uart 44e09000.serial: no wakeirq for uart0
44e09000.serial: ttyO0 at MMIO 0x44e09000 (irq = 158, base_baud = 3000000) is a OMAP UART0
console [ttyO0] enabled
omap_uart 48022000.serial: no wakeirq for uart1
48022000.serial: ttyO1 at MMIO 0x48022000 (irq = 159, base_baud = 3000000) is a OMAP UART1
omap_uart 48024000.serial: no wakeirq for uart2
48024000.serial: ttyO2 at MMIO 0x48024000 (irq = 160, base_baud = 3000000) is a OMAP UART2
brd: module loaded
mtdoops: mtd device (mtddev=name/number) must be supplied
libphy: Fixed MDIO Bus: probed
davinci_mdio 4a101000.mdio: davinci mdio revision 1.6
davinci_mdio 4a101000.mdio: detected phy mask fffffffe
random: fast init done
libphy: 4a101000.mdio: probed
davinci_mdio 4a101000.mdio: phy[0]: device 4a101000.mdio:00, driver SMSC LAN8710/LAN8720
cpsw 4a100000.ethernet: Detected MACID = 68:9e:19:8f:7c:44
ehci_hcd: USB 2.0 'Enhanced' Host Controller (EHCI) Driver
ehci-omap: OMAP-EHCI Host Controller driver
usbcore: registered new interface driver usb-storage
am335x-phy-driver 47401300.usb-phy: 47401300.usb-phy supply vcc not found, using dummy regulator
irq: no irq domain found for /ocp/i2c@44e0b000/tps@24 !
am335x-phy-driver 47401b00.usb-phy: 47401b00.usb-phy supply vcc not found, using dummy regulator
musb-hdrc musb-hdrc.1: Failed to request rx1.
omap_rtc 44e3e000.rtc: already running
omap_rtc 44e3e000.rtc: rtc core: registered 44e3e000.rtc as rtc0
i2c /dev entries driver
omap_wdt: OMAP Watchdog Timer Rev 0x01: initial timeout 60 sec
omap_hsmmc 48060000.mmc: Got CD GPIO
usbcore: registered new interface driver usbhid
usbhid: USB HID core driver
oprofile: using arm/armv7
u32 classifier
 Actions configured
NET: Registered protocol family 10
Segment Routing with IPv6
sit: IPv6, IPv4 and MPLS over IPv4 tunneling driver
NET: Registered protocol family 17
Key type dns_resolver registered
omap_voltage_late_init: Voltage driver support not added
ThumbEE CPU extension supported.
Btrfs loaded, crc32c=crc32c-generic
Key type encrypted registered
mmc1: new high speed MMC card at address 0001
mmcblk1: mmc1:0001 S10004 3.56 GiB
mmcblk1boot0: mmc1:0001 S10004 partition 1 4.00 MiB
mmcblk1boot1: mmc1:0001 S10004 partition 2 4.00 MiB
 mmcblk1: p1 p2 p3 p4 < p5 p6 >
tps65217 0-0024: TPS65217 ID 0xe version 1.2
omap_i2c 44e0b000.i2c: bus 0 rev0.11 at 400 kHz
omap_i2c 4802a000.i2c: bus 1 rev0.11 at 50 kHz
omap_i2c 4819c000.i2c: bus 2 rev0.11 at 100 kHz
musb-hdrc musb-hdrc.1: MUSB HDRC host driver
musb-hdrc musb-hdrc.1: new USB bus registered, assigned bus number 1
hub 1-0:1.0: USB hub found
hub 1-0:1.0: 1 port detected
console [netcon0] enabled
netconsole: network logging started
omap_rtc 44e3e000.rtc: setting system clock to 2018-02-15 12:46:24 UTC (1518698784)
EXT4-fs (mmcblk1p2): mounted filesystem with ordered data mode. Opts: (null)
VFS: Mounted root (ext4 filesystem) on device 179:2.
devtmpfs: mounted
Freeing unused kernel memory: 1024K
INIT: version 2.88 booting
Starting udev
udevd[111]: starting version 3.2.2
udevd[112]: starting eudev-3.2.2
EXT4-fs (mmcblk1p2): re-mounted. Opts: data=ordered
INIT: Entering runlevel: 5
Configuring network interfaces... net eth0: initializing cpsw version 1.12 (0)
cpsw 4a100000.ethernet: initialized cpsw ale version 1.4
cpsw 4a100000.ethernet: ALE Table size 1024
SMSC LAN8710/LAN8720 4a101000.mdio:00: attached PHY driver [SMSC LAN8710/LAN8720] (mii_bus:phy_addr=4a101000.mdio:00, irq=-1)
IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready
udhcpc (v1.24.1) started
Sending discover...
cpsw 4a100000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx
IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
Sending discover...
Sending select for 10.1.1.73...
Lease of 10.1.1.73 obtained, lease time 7200
/etc/udhcpc.d/50default: Adding DNS 10.1.0.1
done.
Starting OpenBSD Secure Shell server: sshd
done.
Starting syslogd/klogd: done
Starting web server: apache2.

Poky (Yocto Project Reference Distro) 2.4.2 beaglebone /dev/ttyO0

beaglebone login:

You can see it is mounting /dev/mmcblk1p2 as root.

I think something is wrong well beyond something with uEnv.txt. I can delete uEnv.txt from my boot partition (/dev/mmcblk1p1) and the system still boots fine. That shouldn't be the case. In fact I can seemingly strip my boot partition down to just MLO and u-boot.img, and the system still boots. It seems to be pulling the flattened device tree and uEnv from /dev/mmcblk1p2 /boot directory instead (the system won't boot if I delete files there).

So it's as if either /dev/mmcblk1p2 or partition 2 is hard coded somehow, though I can't find any proof of that. Does anybody know what might be going on and how I can enable my system to boot from either of my root file systems?

Here are my default u-boot settings:

arch=arm
args_mmc=run finduuid;setenv bootargs console=$console $optargs root=PARTUUID=$uuid rw rootfstype=$mmcrootfstype
baudrate=115200
board=am335x
board_name=A335BNLT
board_rev=00C0
board_serial=0816BBBK018E
boot_a_script=load $devtype $devnum:$distro_bootpart $scriptaddr $prefix$script; source $scriptaddr
boot_efi_binary=if fdt addr $fdt_addr_r; then bootefi bootmgr $fdt_addr_r;else bootefi bootmgr $fdtcontroladdr;fi;load $devtype $devnum:$distro_bootpart $kernel_addr_r efi/boot/bootarm.efi; if fdt addr $fdt_addr_r; then bootefi $kernel_addr_r $fdt_addr_r;else bootefi $kernel_addr_r $fdtcontroladdr;fi
boot_extlinux=sysboot $devtype $devnum:$distro_bootpart any $scriptaddr $prefixextlinux/extlinux.conf
boot_fdt=try
boot_fit=0
boot_net_usb_start=usb start
boot_prefixes=/ /boot/
boot_script_dhcp=boot.scr.uimg
boot_scripts=boot.scr.uimg boot.scr
boot_targets=mmc0 legacy_mmc0 mmc1 legacy_mmc1 nand0 pxe dhcp
bootcmd=if test $boot_fit -eq 1; then run update_to_fit; fi; run findfdt; run init_console; run envboot; run distro_bootcmd
bootcmd_dhcp=run boot_net_usb_start; if dhcp $scriptaddr $boot_script_dhcp; then source $scriptaddr; fi;setenv efi_fdtfile $fdtfile; if test -z "$fdtfile" -a -n "$soc"; then setenv efi_fdtfile $soc-$board$boardver.dtb; fi; setenv efi_old_vci $bootp_vci;setenv efi_old_arch $bootp_arch;setenv bootp_vci PXEClient:Arch:00010:UNDI:003000;setenv bootp_arch 0xa;if dhcp $kernel_addr_r; then tftpboot $fdt_addr_r dtb/$efi_fdtfile;if fdt addr $fdt_addr_r; then bootefi $kernel_addr_r $fdt_addr_r; else bootefi $kernel_addr_r $fdtcontroladdr;fi;fi;setenv bootp_vci $efi_old_vci;setenv bootp_arch $efi_old_arch;setenv efi_fdtfile;setenv efi_old_arch;setenv efi_old_vci;
bootcmd_legacy_mmc0=setenv mmcdev 0; setenv bootpart 0:2 ; run mmcboot
bootcmd_legacy_mmc1=setenv mmcdev 1; setenv bootpart 1:2 ; run mmcboot
bootcmd_mmc0=setenv devnum 0; run mmc_boot
bootcmd_mmc1=setenv devnum 1; run mmc_boot
bootcmd_nand=run nandboot
bootcmd_pxe=run boot_net_usb_start; dhcp; if pxe get; then pxe boot; fi
bootcount=1
bootdelay=2
bootdir=/boot
bootenvfile=uEnv.txt
bootfile=zImage
bootm_size=0x10000000
bootpart=0:2
bootscript=echo Running bootscript from mmc$mmcdev ...; source $loadaddr
console=ttyO0,115200n8
cpu=armv7
dfu_alt_info_emmc=rawemmc raw 0 3751936;boot part 1 1;rootfs part 1 2;MLO fat 1 1;MLO.raw raw 0x100 0x100;u-boot.img.raw raw 0x300 0x1000;u-env.raw raw 0x1300 0x200;spl-os-args.raw raw 0x1500 0x200;spl-os-image.raw raw 0x1700 0x6900;spl-os-args fat 1 1;spl-os-image fat 1 1;u-boot.img fat 1 1;uEnv.txt fat 1 1
dfu_alt_info_mmc=boot part 0 1;rootfs part 0 2;MLO fat 0 1;MLO.raw raw 0x100 0x100;u-boot.img.raw raw 0x300 0x1000;u-env.raw raw 0x1300 0x200;spl-os-args.raw raw 0x1500 0x200;spl-os-image.raw raw 0x1700 0x6900;spl-os-args fat 0 1;spl-os-image fat 0 1;u-boot.img fat 0 1;uEnv.txt fat 0 1
dfu_alt_info_nand=SPL part 0 1;SPL.backup1 part 0 2;SPL.backup2 part 0 3;SPL.backup3 part 0 4;u-boot part 0 5;u-boot-spl-os part 0 6;kernel part 0 8;rootfs part 0 9
dfu_alt_info_ram=kernel ram 0x80200000 0x4000000;fdt ram 0x80f80000 0x80000;ramdisk ram 0x81000000 0x4000000
distro_bootcmd=for target in $boot_targets; do run bootcmd_$target; done
efi_dtb_prefixes=/ /dtb/ /dtb/current/
envboot=mmc dev $mmcdev; if mmc rescan; then echo SD/MMC found on device $mmcdev;if run loadbootscript; then run bootscript;else if run loadbootenv; then echo Loaded env from $bootenvfile;run importbootenv;fi;if test -n $uenvcmd; then echo Running uenvcmd ...;run uenvcmd;fi;fi;fi;
eth1addr=68:9e:19:8f:7c:46
ethaddr=68:9e:19:8f:7c:44
fdt_addr_r=0x88000000
fdtaddr=0x88000000
fdtcontroladdr=9df219f8
fdtfile=undefined
findfdt=if test $board_name = A335BONE; then setenv fdtfile am335x-bone.dtb; fi; if test $board_name = A335BNLT; then setenv fdtfile am335x-boneblack.dtb; fi; if test $board_name = BBBW; then setenv fdtfile am335x-boneblack-wireless.dtb; fi; if test $board_name = BBG1; then setenv fdtfile am335x-bonegreen.dtb; fi; if test $board_name = BBGW; then setenv fdtfile am335x-bonegreen-wireless.dtb; fi; if test $board_name = BBBL; then setenv fdtfile am335x-boneblue.dtb; fi; if test $board_name = A33515BB; then setenv fdtfile am335x-evm.dtb; fi; if test $board_name = A335X_SK; then setenv fdtfile am335x-evmsk.dtb; fi; if test $board_name = A335_ICE; then setenv fdtfile am335x-icev2.dtb; fi; if test $fdtfile = undefined; then echo WARNING: Could not determine device tree to use; fi;
finduuid=part uuid mmc $bootpart uuid
fit_bootfile=fitImage
fit_loadaddr=0x87000000
importbootenv=echo Importing environment from mmc$mmcdev ...; env import -t $loadaddr $filesize
init_console=if test $board_name = A335_ICE; then setenv console ttyO3,115200n8;else setenv console ttyO0,115200n8;fi;
kernel_addr_r=0x82000000
load_efi_dtb=load $devtype $devnum:$distro_bootpart $fdt_addr_r $prefix$efi_fdtfile
loadaddr=0x82000000
loadbootenv=fatload mmc $mmcdev $loadaddr $bootenvfile
loadbootscript=load mmc $mmcdev $loadaddr boot.scr
loadfdt=load $devtype $bootpart $fdtaddr $bootdir/$fdtfile
loadfit=run args_mmc; bootm $loadaddr#$fdtfile;
loadimage=load $devtype $bootpart $loadaddr $bootdir/$bootfile
loadramdisk=load mmc $mmcdev $rdaddr ramdisk.gz
mmc_boot=if mmc dev $devnum; then setenv devtype mmc; run scan_dev_for_boot_part; fi
mmcboot=mmc dev $mmcdev; setenv devnum $mmcdev; setenv devtype mmc; if mmc rescan; then echo SD/MMC found on device $mmcdev;if run loadimage; then if test $boot_fit -eq 1; then run loadfit; else run mmcloados;fi;fi;fi;
mmcdev=0
mmcloados=run args_mmc; if test $boot_fdt = yes || test $boot_fdt = try; then if run loadfdt; then bootz $loadaddr - $fdtaddr; else if test $boot_fdt = try; then bootz; else echo WARN: Cannot load the DT; fi; fi; else bootz; fi;
mmcrootfstype=ext4 rootwait
mtdids=nand0=nand.0
mtdparts=mtdparts=nand.0:128k(NAND.SPL),128k(NAND.SPL.backup1),128k(NAND.SPL.backup2),128k(NAND.SPL.backup3),256k(NAND.u-boot-spl-os),1m(NAND.u-boot),128k(NAND.u-boot-env),128k(NAND.u-boot-env.backup1),8m(NAND.kernel),-(NAND.file-system)
nandargs=setenv bootargs console=$console $optargs root=$nandroot rootfstype=$nandrootfstype
nandboot=echo Booting from nand ...; run nandargs; nand read $fdtaddr NAND.u-boot-spl-os; nand read $loadaddr NAND.kernel; bootz $loadaddr - $fdtaddr
nandroot=ubi0:rootfs rw ubi.mtd=NAND.file-system,2048
nandrootfstype=ubifs rootwait=1
netargs=setenv bootargs console=$console $optargs root=/dev/nfs nfsroot=$serverip:$rootpath,$nfsopts rw ip=dhcp
netboot=echo Booting from network ...; setenv autoload no; dhcp; run netloadimage; run netloadfdt; run netargs; bootz $loadaddr - $fdtaddr
netloadfdt=tftp $fdtaddr $fdtfile
netloadimage=tftp $loadaddr $bootfile
nfsopts=nolock
partitions=uuid_disk=$uuid_gpt_disk;name=rootfs,start=2MiB,size=-,uuid=$uuid_gpt_rootfs
pxefile_addr_r=0x80100000
ramargs=setenv bootargs console=$console $optargs root=$ramroot rootfstype=$ramrootfstype
ramboot=echo Booting from ramdisk ...; run ramargs; bootz $loadaddr $rdaddr $fdtaddr
ramdisk_addr_r=0x88080000
ramroot=/dev/ram0 rw
ramrootfstype=ext2
rdaddr=0x88080000
rootpath=/export/rootfs
scan_dev_for_boot=echo Scanning $devtype $devnum:$distro_bootpart...; for prefix in $boot_prefixes; do run scan_dev_for_extlinux; run scan_dev_for_scripts; done;run scan_dev_for_efi;
scan_dev_for_boot_part=part list $devtype $devnum -bootable devplist; env exists devplist || setenv devplist 1; for distro_bootpart in $devplist; do if fstype $devtype $devnum:$distro_bootpart bootfstype; then run scan_dev_for_boot; fi; done
scan_dev_for_efi=setenv efi_fdtfile $fdtfile; if test -z "$fdtfile" -a -n "$soc"; then setenv efi_fdtfile $soc-$board$boardver.dtb; fi; for prefix in $efi_dtb_prefixes; do if test -e $devtype $devnum:$distro_bootpart $prefix$efi_fdtfile; then run load_efi_dtb; fi;done;if test -e $devtype $devnum:$distro_bootpart efi/boot/bootarm.efi; then echo Found EFI removable media binary efi/boot/bootarm.efi; run boot_efi_binary; echo EFI LOAD FAILED: continuing...; fi; setenv efi_fdtfile
scan_dev_for_extlinux=if test -e $devtype $devnum:$distro_bootpart $prefixextlinux/extlinux.conf; then echo Found $prefixextlinux/extlinux.conf; run boot_extlinux; echo SCRIPT FAILED: continuing...; fi
scan_dev_for_scripts=for script in $boot_scripts; do if test -e $devtype $devnum:$distro_bootpart $prefix$script; then echo Found U-Boot script $prefix$script; run boot_a_script; echo SCRIPT FAILED: continuing...; fi; done
scriptaddr=0x80000000
soc=am33xx
spiargs=setenv bootargs console=$console $optargs root=$spiroot rootfstype=$spirootfstype
spiboot=echo Booting from spi ...; run spiargs; sf probe $spibusno:0; sf read $loadaddr $spisrcaddr $spiimgsize; bootz $loadaddr
spibusno=0
spiimgsize=0x362000
spiroot=/dev/mtdblock4 rw
spirootfstype=jffs2
spisrcaddr=0xe0000
static_ip=$ipaddr:$serverip:$gatewayip:$netmask:$hostname::off
stderr=serial@44e09000
stdin=serial@44e09000
stdout=serial@44e09000
update_to_fit=setenv loadaddr $fit_loadaddr; setenv bootfile $fit_bootfile
usb_boot=usb start; if usb dev $devnum; then setenv devtype usb; run scan_dev_for_boot_part; fi
vendor=ti
ver=U-Boot 2018.01 (Feb 15 2018 - 13:50:14 -0500)

Environment size: 9701/131068 bytes

Also, here are a list of commands that when entered manually in u-boot, cause the system to boot perfectly:

setenv bootfile zImage
setenv fdtfile am335x-boneblack.dtb
setenv loadaddr 0x80007fc0
setenv fdtaddr 0x80F80000
setenv console ttyO0,115200
setenv mmcroot /dev/mmcblk1p3
setenv mmcrootfstype ext4
setenv loadfdt fatload mmc 1:1 $fdtaddr $fdtfile
setenv loaduimage fatload mmc 1:1 $loadaddr $bootfile
setenv bootargs console=$console $optargs root=$mmcroot rootfstype=$mmcrootfstype
mmc rescan
run loaduimage
run loadfdt
bootz $loadaddr - $fdtaddr

Only the envboot target will look for uEnv.txt. This target is only run once, not once for each device. So the boot process tries that, fails (all of the Card did not.. messages) and moves on to distro_boot and succeeds in time. If you set mmcdev=1 and saveenv, it should then look for uEnv.txt there, and then it might work.