Computer Organization and Design RISC-V Edition: The Hardware Software Interface (The Morgan Kaufmann Series in Computer Architecture and Design)

For something more on the high level digital side, I'd suggest Patterson's Computer Organization & Design: https://www.amazon.com/Computer-Organization-Design-RISC-V-Architecture/dp/0128203315 I've heard good things about Harris' version, which covers digital logic fundamentals: https://www.amazon.com/Digital-Design-Computer-Architecture-Harris/dp/0123944244/

Look into college textbooks. This one I learned from and built a pretty powerful embedded SoC based off of (plus a few other sources) https://www.amazon.com/Computer-Organization-Design-RISC-V-Architecture/dp/0128203315 For bootloaders and loading software, you’re going to want to look into documentation/OS college textbooks. Your bootloader needs to 1) load the program from storage into memory. 2) set basic registers according to an ABI and 3) jump to the start of the program. You’ll need to define some custom memory map.