This procedure overwrites the MBR and all partitions on the eMMC with images from the SD card.
The U-Boot environment is preserved.
Default boot mode of TQMa28 is eMMC boot:
LCD_DATA[4..0] = {0,1,0,0,1}
Please note: At this state there is no way to extract the image sizes from the SD card.
Without them calculation of required sectors to store the images is not possible.
Therefore using this update method will grab and overwrite whole uboot/kernel partitions respectively.
Updating U-Boot via ethernet does not create a redundant copy as expected by the MX28 as a fall-back level.