looking for tutorials/documentation on bootloaders for arm processors

I was recently tasked with looking into the boot loader for an A55 processor chipset , will need to enable multiple cores and maybe setup the stack for each of them as well .

I am completely new to this domain , i am proficient in C and have basic knowledge of asm.

Need to learn about bootloaders, stack initialisation, multi-core bootup procedure and so on.....

Please share any tutorial links or documentation that you feel would help in this regard. Thanks.