I have been attemptiong to get an elf format load of FreeRTOS to either be run by grub 2.02, or placed into the system by grub's insmod. Various error messages later, I wonder if anyone else has been able to do this, and what the exact procedure is.
I have already gone through the loop with GRUBMODLICENSE() and MODULE_LICENSE().
My ultimate goal is to have FreeRTOS boot on power-up, like Linux does.
Unfortunately you have not mentioned which architecture you are using. My only experience with grub is on the Quark, for which instructions are provided on this page: http://www.freertos.org/RTOSIntelQuarkGalileoGCC.html
I am using an Advantech PCM-3356F, which is a standard PC. It has an AMI BIOS and an AMD 686 processor. I installed Linux Mint 17.2, which is why it has grub.