Build a minimal kernel for RISC-V

Part 1. Explore RISC-V/QEMU/U-Boot/OpenSBI

Get familiar with QEMU virtual machine firmware loading, kernel loading workflow.

• 00: Run Linux with QEMU
• 01: Run U-Boot with QEMU
• 02: Run OpenSBI with QEMU

Part 2. Bare Metal RISC-V

Write a bare metal firmware for QEMU virt device, which just prints Hello, RISC-V!

• 03: Bare Metal Hello RISC-V
• 04: Bare Metal Hello RISC-V (C Language Version)

~~Switch to sifive_u, because virt is not well documented!~~

• ~~04.1: Bare Metal Hello Sifive_u~~

After some attempts, I found that I had to revert back to virt because sifive_u doesn't support mmio and PCI-E.

Part 3. Interrupts and Process Scheduling

• 05: Interrupt Basics (TODO)
• 06: Timer Interrupt (Code Completed)
• 07: Timer Interrupt-based Process Scheduling (Code Completed)
• 08: UART Interrupt (Partially Completed)

Appendix

• Appendix-00: Assembly and Linking Basics