This is a recap of what we have done so far.

[package]
name = "start"
version = "0.2.0"

[dependencies]
panic-halt = "~0.2"
microbit="~0.7"
cortex-m-rt="~0.6"

#![no_std]
#![no_main]

extern crate cortex_m_rt;
extern crate microbit;
extern crate panic_halt;

use cortex_m_rt::entry;

#[entry]
fn main() -> ! {
    let _y;
    let x = 42;
    _y = x;
    loop {}
}

# Configure builds for our target, the micro:bit's architecture
[target.thumbv6m-none-eabi]
# Execute binary using gdb when calling cargo run
runner = "arm-none-eabi-gdb"
# Tweak to the linking process required by the cortex-m-rt crate
rustflags = [
    "-C", "link-arg=-Tlink.x",
    # The LLD linker is selected by default
    #"-C", "linker=arm-none-eabi-ld",
]

# Automatically select this target when cargo building this project
[build]
target = "thumbv6m-none-eabi"

# Connects GDB to OpenOCD server port
target remote :3333
# (optional) Unmangle function names when debugging
set print asm-demangle on
# Load your program, breaks at entry
load
# (optional) Add breakpoint at function
break main
# Continue with execution
continue