rust-raspberrypi-OS-tutorials/01_wait_forever

Tutorial 01 - Wait Forever

tl;dr

Project skeleton is set up; Code just halts all CPU cores executing the kernel code.

• Toolchain: cargo xbuild tools (xrustc, xclippy) and the aarch64-unknown-none-softfloat target are used for building AArch64 bare-metal code.
• Makefile targets:
  • doc: Generate documentation.
  • qemu: Run the kernel in QEMU
  • clippy
  • clean
  • readelf: Inspect the ELF output.
  • objdump: Inspect the assembly.
  • nm: Inspect the symbols.
• Code is organized into kernel, arch and BSP (Board Support Package) parts.
  • Conditional compilation includes respective arch and BSP according to user-supplied arguments.
• Custom link.ld linker script.
  • Load address at 0x80_000
  • Only .text section.
• main.rs: Important inner attributes:
  • #![no_std], #![no_main]
• Assembly _start() function that executes wfe (Wait For Event), halting all cores that are executing _start().
• We (have to) define a #[panic_handler] function.
  • Just waits infinitely for a cpu event.

Give it a try

In the project folder, invoke QEMU and observe the CPU core spinning on wfe:

make qemu
[...]
IN: 
0x00080000:  d503205f  wfe      
0x00080004:  17ffffff  b        #0x80000