Courses about deploying Linux on embedded systems
studying the Beaglebone and the documentation for how that works, is a great way to see how to set up and run linux on a powerful but small ARM chip like the TI AM3358 (ARM A8 or A9 I believe).

They go through the whole process of how to interface with u-boot and the low-level processes, and then the kernel image stuff.

I worked for a company that was using the beaglebone as a development board for the firmware guys, while the hardware guys made a custom PCB and integrated all their industrial control circuits into it.