If the bootloader has been erased from the storage media (or written with an invalid image) and the target does not boot, you can recover the target booting from USB device port.
To boot in USB debug mode and into the bootloader, follow these steps:
Linux host computer.
Root/Administrator permissions on your development computer.
A micro USB cable.
The imx_usb tool repository. You can clone it on your development computer and follow the instructions to compile it here.
git checkout 349286e25c3fd9b2d31b31e962340123bbc62d44
Boot U-Boot in USB debug mode
Connect the micro USB cable to the USB device port of the SBC (bottom layer, under the USB host connectors) and the other end to the development computer.
Close the BOOT MODE0 micro switch (SW3) near the XBee connector of the SBC.
Open a serial terminal at 115200/8/n/1.
On the host computer run the imx_usb tool from the imx_usb directory as root with the U-Boot file to boot as parameter, for example:
sudo /path/to/imx_usb/repo/imx_usb /path/to/u-boot-ccimx6sbc.imx
On the serial terminal, you will see the device starting U-Boot.
From the U-boot prompt, refer to Program the Android firmware for instructions to program a Digi Embedded Android system.