I read online that we can run U-boot scripts. I just want some clarification. If I write a U-boot script on my embedded system, which basically mounts a USB flash drive that's plugged in, send a file to Host via TFTP, then proceeds to mount the Linux OS. Is this possible? (Note that I want to do something out of the ordinary. My Linux OS lives on an SD card, and U-Boot needs load that, but what I'm asking is the ability to transfer a file from embedded system with my attached USB flash drive to my PC, then proceed to load my linux os.) The reason for doing this is that the file is time critical for my PC to retrieve within seconds of my embedded system powering on. I know it's much better to let my OS load, and then allow it to send the file, but I do not want to go that route. I specially want to send the file in 2 seconds rather than waiting 10 seconds for my Linux to boot. Also, is it possible to have the script run in parallel with the linux boot. For example If I have 2GB of files to transfer from USB Flashdrive, and so that will continue to transfer, but in parallel the linux OS boots from U-Boot? 
Run application from U-boot and boot linux
linux kernel;dual boot;arm;u boot