Can't boot from sd-card on BeagleBone Black

[Pavel Yermolenko]

Hello,

I've tried two different default configurations while building u-boot:

  * am335x_boneblack_vboot_defconfig
  * am335x_evm_defconfig

I formatted sd-card with this script:
https://github.com/PacktPublishing/Mastering-Embedded-Linux-Programming-Second-Edition/blob/master/format-sdcard.sh
Then I copied *MLO* and *u-boot.img* into the boot partition.
Here is boot log for am335x_boneblack_vboot_defconfig case (for 
am335x_evm_defconfig it's similar):

    |U-Boot SPL 2020.10-rc3 (Aug 28 2020 - 10:16:38 +0200)|
    |WDT: Not found!
    Trying to boot from MMC1
    Loading Environment from FAT... *** Warning - bad CRC, using default
    environment
    Loading Environment from MMC... *** Warning - bad CRC, using default
    environment
      U-Boot 2020.10-rc3 (Aug 28 2020 - 10:16:38 +0200)
      CPU : AM335X-GP rev 2.1
    Model: TI AM335x BeagleBone Black
    DRAM: 512 MiB
    MMC: OMAP SD/MMC: 0, OMAP SD/MMC: 1
    Loading Environment from FAT... *** Warning - bad CRC, using default
    environment
    Loading Environment from MMC... *** Warning - bad CRC, using default
    environment
      <ethaddr> not set. Validating first E-fuse MAC
    Net: eth2: ethernet at 4a100000, eth3: usb_ether
    Press SPACE to abort autoboot in 2 seconds
    switch to partitions #0, OK
    mmc0 is current device
    SD/MMC found on device 0
    Failed to load 'boot.scr'
    Failed to load 'uEnv.txt'
    switch to partitions #0, OK
    mmc0 is current device
    Scanning mmc 0:1...
    switch to partitions #0, OK
    mmc0 is current device
    SD/MMC found on device 0
    Failed to load '/boot/zImage'
    switch to partitions #0, OK
    mmc1(part 0) is current device
    Scanning mmc 1:1...
    Found /boot/extlinux/extlinux.conf|

As you see, it tries to boot from MMC1 (I suppose that it's sd-card), it 
fails to boot from MMC1, then it switches to eMMC (where is full Linux, 
i.e. boot + kernel) and boots successfully from eMMC.

There are warnings: "bad CRC". Probably this is the cause of boot failure ?
Could it be problem of copying of u-boot files ... or erroneous 
formatting of sd-card.
Have someone an idea how to check these issues.
Thanks.
Sincerely,
Pavel.