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rust-raspberrypi-OS-tutorials/01_wait_forever/README.md
Andre Richter c4f9432e13
Remove xbuild. Use upstream aarch64 rust-std 🎉 🦀 
`rustup target add aarch64-unknown-none-softfloat` is now a thing.
It is no longer required to build rust-std on-demand with `xbuild`.

This reduces compile-times significantly.
2020-04-07 23:17:48 +02:00

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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
    • Only .text section.
  • main.rs: Important inner attributes:
    • #![no_std], #![no_main]
  • cpu.S: 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.

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