Finally, prepare the i.MX6 Quad board for U-Boot:

1. Connect to your i.MX6 Quad board with a serial connection at a baud rate of 115200.
2. Set the following environment variables in the U-Boot terminal:

   setenv bootcmd_demo_dt 'mmc dev 1;
   fatload mmc 1:1 20000000 demo.image;
   fatload mmc 1:1 4FFE0000 imx6q-sabrelite.dtb;
   bootm 20000000 - 4FFE0000'
   
   setenv bootcmd 'run bootcmd_demo_dt'
   saveenv

   Note: The file demo.image was built with the mkimage tool in Building U-Boot Image.

3. Reset the i.MX6 Quad board.

Now your i.MX6 Quad board is ready to run your application.