This gist is for the ConnectCore i.MX6UL starter kit.
If you want to launch linux using a micro SD card, you will need at least a 8GB card.
In order to boot the Digi ConnectCore i.MX6UL from the micro SD first you have to divide the micro SD into 2 partitions. The first one should be FAT32 so it can hold the images and the second one should be ext4 since it is going to have the root filesytem.
You can use any tool like gparted to do this. Once you have the microSD formated you will need to copy the corresponding files to the FAT32 partition. For the starter board (ccimx6ulstarter) the files are:
zImage-ccimx6ulstarter.bin
zImage-imx6ul-ccimx6ulstarter-id129.dtb
You will also need to expand the root filesystem in the ext4 partition, for the starter board this file is the one that has the image name and ends in -ccimx6ulstarter.tar.bz2 for example:
core-image-base-ccimx6ulstarter.tar.bz2
Then connect to the board via serial and in U-boot write this configuration:
setenv mmcroot /dev/mmcblk1p2 rw
setenv bootargs console=${console},${baudrate} ${bootargs_linux} root=${mmcroot} ${bootargs_once} ${extra_bootargs}
setenv load_kernel_mmc fatload mmc 0:1 ${loadaddr} /zImage-ccimx6ulstarter.bin
setenv load_fdt_mmc fatload mmc 0:1 ${fdt_addr} /zImage-imx6ul-ccimx6ulstarter-id129.dtb
setenv bootcmd 'mmc rescan; run load_kernel_mmc; run load_fdt_mmc; bootz ${loadaddr} - ${fdt_addr}'
saveenv
Once the environment variables are set proceed to restart the board by running reset and it should boot from the uSD.