rust-raspberrypi-OS-tutorials/01_wait_forever

Tutorial 01 - Wait Forever

tl;dr

The project skeleton is set up; A small piece of assembly code runs that just halts all CPU cores executing the kernel code.

Building

• 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 to look at

• Custom link.ld linker script.
  • Load address at 0x80_000 for RPi and 0x20400000 for HiFive1.
  • Only .text section.
• main.rs: Important inner attributes:
  • #![no_std], #![no_main]
• cpu.S: Assembly _start() function that executes wfe (Wait For Event) for RPi and wfi (Wait For Interrupt) for HiFive1, halting all cores that are executing _start().
• We (have to) define a #[panic_handler] function.
  • Just waits infinitely for a cpu event.

Test it

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

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