U-Boot is a bootloader, which supports some i.MX SoCs.
U-boot FW Printenv FW Env File
I.MX25 PDK U-boot SplashScreen
Compiling U-Boot for i.MX27ADS
Blink i.MX31 PDK LEDs Using U-Boot
Script to Flash a Linux System into a SD card
All Boards LTIB Creating Uimage Uboot