~athorp96/embedded-rust-experiments

3ba2d1ee8f9cf9dcaba0affd70a1e05b77ac546e — Andrew Thorp 1 year, 12 days ago
initial commit
A  => .cargo-ok +0 -0
A  => .cargo/config +40 -0
@@ 1,40 @@
[target.thumbv7m-none-eabi]
# uncomment this to make `cargo run` execute programs on QEMU
# runner = "qemu-system-arm -cpu cortex-m3 -machine lm3s6965evb -nographic -semihosting-config enable=on,target=native -kernel"

[target.'cfg(all(target_arch = "arm", target_os = "none"))']
# uncomment ONE of these three option to make `cargo run` start a GDB session
# which option to pick depends on your system
# runner = "arm-none-eabi-gdb -q -x openocd.gdb"
# runner = "gdb-multiarch -q -x openocd.gdb"
# runner = "gdb -q -x openocd.gdb"

rustflags = [
  # This is needed if your flash or ram addresses are not aligned to 0x10000 in memory.x
  # See https://github.com/rust-embedded/cortex-m-quickstart/pull/95
  "-C", "link-arg=--nmagic",

  # LLD (shipped with the Rust toolchain) is used as the default linker
  "-C", "link-arg=-Tlink.x",

  # if you run into problems with LLD switch to the GNU linker by commenting out
  # this line
  # "-C", "linker=arm-none-eabi-ld",

  # if you need to link to pre-compiled C libraries provided by a C toolchain
  # use GCC as the linker by commenting out both lines above and then
  # uncommenting the three lines below
  # "-C", "linker=arm-none-eabi-gcc",
  # "-C", "link-arg=-Wl,-Tlink.x",
  # "-C", "link-arg=-nostartfiles",
]

[build]
# Pick ONE of these compilation targets
# target = "thumbv6m-none-eabi"        # Cortex-M0 and Cortex-M0+
target = "thumbv7m-none-eabi"        # Cortex-M3
# target = "thumbv7em-none-eabi"       # Cortex-M4 and Cortex-M7 (no FPU)
# target = "thumbv7em-none-eabihf"     # Cortex-M4F and Cortex-M7F (with FPU)
# target = "thumbv8m.base-none-eabi"   # Cortex-M23
# target = "thumbv8m.main-none-eabi"   # Cortex-M33 (no FPU)
# target = "thumbv8m.main-none-eabihf" # Cortex-M33 (with FPU)

A  => .gitignore +13 -0
@@ 1,13 @@
**/*.rs.bk
.#*
.gdb_history
Cargo.lock
target/

# editor files
.vscode/*
!.vscode/*.md
!.vscode/*.svd
!.vscode/launch.json
!.vscode/tasks.json
!.vscode/extensions.json

A  => Cargo.toml +36 -0
@@ 1,36 @@
[package]
authors = ["Andrew Thorp <andrew.thorp.dev@gmail.com>"]
edition = "2018"
readme = "README.md"
name = "app"
version = "0.1.0"

[dependencies]
cortex-m = "0.6.0"
cortex-m-rt = "0.6.10"
cortex-m-semihosting = "0.3.3"
panic-halt = "0.2.0"

# Uncomment for the panic example.
# panic-itm = "0.4.1"

# Uncomment for the allocator example.
# alloc-cortex-m = "0.4.0"

# Uncomment for the device example.
# Update `memory.x`, set target to `thumbv7em-none-eabihf` in `.cargo/config`,
# and then use `cargo build --examples device` to build it.
# [dependencies.stm32f3]
# features = ["stm32f303", "rt"]
# version = "0.7.1"

# this lets you use `cargo fix`!
[[bin]]
name = "app"
test = false
bench = false

[profile.release]
codegen-units = 1 # better optimizations
debug = true # symbols are nice and they don't increase the size on Flash
lto = true # better optimizations

A  => README.md +135 -0
@@ 1,135 @@
# `cortex-m-quickstart`

> A template for building applications for ARM Cortex-M microcontrollers

This project is developed and maintained by the [Cortex-M team][team].

## Dependencies

To build embedded programs using this template you'll need:

- Rust 1.31, 1.30-beta, nightly-2018-09-13 or a newer toolchain. e.g. `rustup
  default beta`

- The `cargo generate` subcommand. [Installation
  instructions](https://github.com/ashleygwilliams/cargo-generate#installation).

- `rust-std` components (pre-compiled `core` crate) for the ARM Cortex-M
  targets. Run:

``` console
$ rustup target add thumbv6m-none-eabi thumbv7m-none-eabi thumbv7em-none-eabi thumbv7em-none-eabihf
```

## Using this template

**NOTE**: This is the very short version that only covers building programs. For
the long version, which additionally covers flashing, running and debugging
programs, check [the embedded Rust book][book].

[book]: https://rust-embedded.github.io/book

0. Before we begin you need to identify some characteristics of the target
  device as these will be used to configure the project:

- The ARM core. e.g. Cortex-M3.

- Does the ARM core include an FPU? Cortex-M4**F** and Cortex-M7**F** cores do.

- How much Flash memory and RAM does the target device has? e.g. 256 KiB of
  Flash and 32 KiB of RAM.

- Where are Flash memory and RAM mapped in the address space? e.g. RAM is
  commonly located at address `0x2000_0000`.

You can find this information in the data sheet or the reference manual of your
device.

In this example we'll be using the STM32F3DISCOVERY. This board contains an
STM32F303VCT6 microcontroller. This microcontroller has:

- A Cortex-M4F core that includes a single precision FPU

- 256 KiB of Flash located at address 0x0800_0000.

- 40 KiB of RAM located at address 0x2000_0000. (There's another RAM region but
  for simplicity we'll ignore it).

1. Instantiate the template.

``` console
$ cargo generate --git https://github.com/rust-embedded/cortex-m-quickstart
 Project Name: app
 Creating project called `app`...
 Done! New project created /tmp/app

$ cd app
```

2. Set a default compilation target. There are four options as mentioned at the
   bottom of `.cargo/config`. For the STM32F303VCT6, which has a Cortex-M4F
   core, we'll pick the `thumbv7em-none-eabihf` target.

``` console
$ tail -n6 .cargo/config
```

``` toml
[build]
# Pick ONE of these compilation targets
# target = "thumbv6m-none-eabi"    # Cortex-M0 and Cortex-M0+
# target = "thumbv7m-none-eabi"    # Cortex-M3
# target = "thumbv7em-none-eabi"   # Cortex-M4 and Cortex-M7 (no FPU)
target = "thumbv7em-none-eabihf" # Cortex-M4F and Cortex-M7F (with FPU)
```

3. Enter the memory region information into the `memory.x` file.

``` console
$ cat memory.x
/* Linker script for the STM32F303VCT6 */
MEMORY
{
  /* NOTE 1 K = 1 KiBi = 1024 bytes */
  FLASH : ORIGIN = 0x08000000, LENGTH = 256K
  RAM : ORIGIN = 0x20000000, LENGTH = 40K
}
```

4. Build the template application or one of the examples.

``` console
$ cargo build
```

## VS Code

This template includes launch configurations for debugging CortexM programs with Visual Studio Code located in the `.vscode/` directory.  
See [.vscode/README.md](./.vscode/README.md) for more information.  
If you're not using VS Code, you can safely delete the directory from the generated project.

# License

This template is licensed under either of

- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
  http://www.apache.org/licenses/LICENSE-2.0)

- MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)

at your option.

## Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.

## Code of Conduct

Contribution to this crate is organized under the terms of the [Rust Code of
Conduct][CoC], the maintainer of this crate, the [Cortex-M team][team], promises
to intervene to uphold that code of conduct.

[CoC]: https://www.rust-lang.org/policies/code-of-conduct
[team]: https://github.com/rust-embedded/wg#the-cortex-m-team

A  => build.rs +31 -0
@@ 1,31 @@
//! This build script copies the `memory.x` file from the crate root into
//! a directory where the linker can always find it at build time.
//! For many projects this is optional, as the linker always searches the
//! project root directory -- wherever `Cargo.toml` is. However, if you
//! are using a workspace or have a more complicated build setup, this
//! build script becomes required. Additionally, by requesting that
//! Cargo re-run the build script whenever `memory.x` is changed,
//! updating `memory.x` ensures a rebuild of the application with the
//! new memory settings.

use std::env;
use std::fs::File;
use std::io::Write;
use std::path::PathBuf;

fn main() {
    // Put `memory.x` in our output directory and ensure it's
    // on the linker search path.
    let out = &PathBuf::from(env::var_os("OUT_DIR").unwrap());
    File::create(out.join("memory.x"))
        .unwrap()
        .write_all(include_bytes!("memory.x"))
        .unwrap();
    println!("cargo:rustc-link-search={}", out.display());

    // By default, Cargo will re-run a build script whenever
    // any file in the project changes. By specifying `memory.x`
    // here, we ensure the build script is only re-run when
    // `memory.x` is changed.
    println!("cargo:rerun-if-changed=memory.x");
}

A  => examples/allocator.rs +56 -0
@@ 1,56 @@
//! How to use the heap and a dynamic memory allocator
//!
//! This example depends on the alloc-cortex-m crate so you'll have to add it to your Cargo.toml:
//!
//! ``` text
//! # or edit the Cargo.toml file manually
//! $ cargo add alloc-cortex-m
//! ```
//!
//! ---

#![feature(alloc_error_handler)]
#![no_main]
#![no_std]

extern crate alloc;
use panic_halt as _;

use self::alloc::vec;
use core::alloc::Layout;

use alloc_cortex_m::CortexMHeap;
use cortex_m::asm;
use cortex_m_rt::entry;
use cortex_m_semihosting::{hprintln, debug};

// this is the allocator the application will use
#[global_allocator]
static ALLOCATOR: CortexMHeap = CortexMHeap::empty();

const HEAP_SIZE: usize = 1024; // in bytes

#[entry]
fn main() -> ! {
    // Initialize the allocator BEFORE you use it
    unsafe { ALLOCATOR.init(cortex_m_rt::heap_start() as usize, HEAP_SIZE) }

    // Growable array allocated on the heap
    let xs = vec![0, 1, 2];

    hprintln!("{:?}", xs).unwrap();

    // exit QEMU
    // NOTE do not run this on hardware; it can corrupt OpenOCD state
    debug::exit(debug::EXIT_SUCCESS);

    loop {}
}

// define what happens in an Out Of Memory (OOM) condition
#[alloc_error_handler]
fn alloc_error(_layout: Layout) -> ! {
    asm::bkpt();

    loop {}
}

A  => examples/crash.rs +96 -0
@@ 1,96 @@
//! Debugging a crash (exception)
//!
//! Most crash conditions trigger a hard fault exception, whose handler is defined via
//! `exception!(HardFault, ..)`. The `HardFault` handler has access to the exception frame, a
//! snapshot of the CPU registers at the moment of the exception.
//!
//! This program crashes and the `HardFault` handler prints to the console the contents of the
//! `ExceptionFrame` and then triggers a breakpoint. From that breakpoint one can see the backtrace
//! that led to the exception.
//!
//! ``` text
//! (gdb) continue
//! Program received signal SIGTRAP, Trace/breakpoint trap.
//! __bkpt () at asm/bkpt.s:3
//! 3         bkpt
//!
//! (gdb) backtrace
//! #0  __bkpt () at asm/bkpt.s:3
//! #1  0x080030b4 in cortex_m::asm::bkpt () at $$/cortex-m-0.5.0/src/asm.rs:19
//! #2  rust_begin_unwind (args=..., file=..., line=99, col=5) at $$/panic-semihosting-0.2.0/src/lib.rs:87
//! #3  0x08001d06 in core::panicking::panic_fmt () at libcore/panicking.rs:71
//! #4  0x080004a6 in crash::hard_fault (ef=0x20004fa0) at examples/crash.rs:99
//! #5  0x08000548 in UserHardFault (ef=0x20004fa0) at <exception macros>:10
//! #6  0x0800093a in HardFault () at asm.s:5
//! Backtrace stopped: previous frame identical to this frame (corrupt stack?)
//! ```
//!
//! In the console output one will find the state of the Program Counter (PC) register at the time
//! of the exception.
//!
//! ``` text
//! panicked at 'HardFault at ExceptionFrame {
//!     r0: 0x2fffffff,
//!     r1: 0x2fffffff,
//!     r2: 0x080051d4,
//!     r3: 0x080051d4,
//!     r12: 0x20000000,
//!     lr: 0x08000435,
//!     pc: 0x08000ab6,
//!     xpsr: 0x61000000
//! }', examples/crash.rs:106:5
//! ```
//!
//! This register contains the address of the instruction that caused the exception. In GDB one can
//! disassemble the program around this address to observe the instruction that caused the
//! exception.
//!
//! ``` text
//! (gdb) disassemble/m 0x08000ab6
//! Dump of assembler code for function core::ptr::read_volatile:
//! 451     pub unsafe fn read_volatile<T>(src: *const T) -> T {
//!    0x08000aae <+0>:     sub     sp, #16
//!    0x08000ab0 <+2>:     mov     r1, r0
//!    0x08000ab2 <+4>:     str     r0, [sp, #8]
//!
//! 452         intrinsics::volatile_load(src)
//!    0x08000ab4 <+6>:     ldr     r0, [sp, #8]
//! -> 0x08000ab6 <+8>:     ldr     r0, [r0, #0]
//!    0x08000ab8 <+10>:    str     r0, [sp, #12]
//!    0x08000aba <+12>:    ldr     r0, [sp, #12]
//!    0x08000abc <+14>:    str     r1, [sp, #4]
//!    0x08000abe <+16>:    str     r0, [sp, #0]
//!    0x08000ac0 <+18>:    b.n     0x8000ac2 <core::ptr::read_volatile+20>
//!
//! 453     }
//!    0x08000ac2 <+20>:    ldr     r0, [sp, #0]
//!    0x08000ac4 <+22>:    add     sp, #16
//!    0x08000ac6 <+24>:    bx      lr
//!
//! End of assembler dump.
//! ```
//!
//! `ldr r0, [r0, #0]` caused the exception. This instruction tried to load (read) a 32-bit word
//! from the address stored in the register `r0`. Looking again at the contents of `ExceptionFrame`
//! we see that the `r0` contained the address `0x2FFF_FFFF` when this instruction was executed.
//!
//! ---

#![no_main]
#![no_std]

use panic_halt as _;

use core::ptr;

use cortex_m_rt::entry;

#[entry]
fn main() -> ! {
    unsafe {
        // read an address outside of the RAM region; this causes a HardFault exception
        ptr::read_volatile(0x2FFF_FFFF as *const u32);
    }

    loop {}
}

A  => examples/device.rs +62 -0
@@ 1,62 @@
//! Using a device crate
//!
//! Crates generated using [`svd2rust`] are referred to as device crates. These crates provide an
//! API to access the peripherals of a device.
//!
//! [`svd2rust`]: https://crates.io/crates/svd2rust
//!
//! This example depends on the [`stm32f3`] crate so you'll have to
//! uncomment it in your Cargo.toml.
//!
//! [`stm32f3`]: https://crates.io/crates/stm32f3
//!
//! ```
//! $ edit Cargo.toml && tail $_
//! [dependencies.stm32f3]
//! features = ["stm32f303", "rt"]
//! version = "0.7.1"
//! ```
//!
//! You also need to set the build target to thumbv7em-none-eabihf,
//! typically by editing `.cargo/config` and uncommenting the relevant target line.
//!
//! ---

#![no_main]
#![no_std]

#[allow(unused_extern_crates)]
use panic_halt as _;

use cortex_m::peripheral::syst::SystClkSource;
use cortex_m_rt::entry;
use cortex_m_semihosting::hprint;
use stm32f3::stm32f303::{interrupt, Interrupt, NVIC};

#[entry]
fn main() -> ! {
    let p = cortex_m::Peripherals::take().unwrap();

    let mut syst = p.SYST;
    let mut nvic = p.NVIC;

    nvic.enable(Interrupt::EXTI0);

    // configure the system timer to wrap around every second
    syst.set_clock_source(SystClkSource::Core);
    syst.set_reload(8_000_000); // 1s
    syst.enable_counter();

    loop {
        // busy wait until the timer wraps around
        while !syst.has_wrapped() {}

        // trigger the `EXTI0` interrupt
        NVIC::pend(Interrupt::EXTI0);
    }
}

#[interrupt]
fn EXTI0() {
    hprint!(".").unwrap();
}

A  => examples/exception.rs +37 -0
@@ 1,37 @@
//! Overriding an exception handler
//!
//! You can override an exception handler using the [`#[exception]`][1] attribute.
//!
//! [1]: https://rust-embedded.github.io/cortex-m-rt/0.6.1/cortex_m_rt_macros/fn.exception.html
//!
//! ---

#![deny(unsafe_code)]
#![no_main]
#![no_std]

use panic_halt as _;

use cortex_m::peripheral::syst::SystClkSource;
use cortex_m::Peripherals;
use cortex_m_rt::{entry, exception};
use cortex_m_semihosting::hprint;

#[entry]
fn main() -> ! {
    let p = Peripherals::take().unwrap();
    let mut syst = p.SYST;

    // configures the system timer to trigger a SysTick exception every second
    syst.set_clock_source(SystClkSource::Core);
    syst.set_reload(8_000_000); // period = 1s
    syst.enable_counter();
    syst.enable_interrupt();

    loop {}
}

#[exception]
fn SysTick() {
    hprint!(".").unwrap();
}

A  => examples/hello.rs +20 -0
@@ 1,20 @@
//! Prints "Hello, world!" on the host console using semihosting

#![no_main]
#![no_std]

use panic_halt as _;

use cortex_m_rt::entry;
use cortex_m_semihosting::{debug, hprintln};

#[entry]
fn main() -> ! {
    hprintln!("Hello, world!").unwrap();

    // exit QEMU
    // NOTE do not run this on hardware; it can corrupt OpenOCD state
    debug::exit(debug::EXIT_SUCCESS);

    loop {}
}

A  => examples/itm.rs +33 -0
@@ 1,33 @@
//! Sends "Hello, world!" through the ITM port 0
//!
//! ITM is much faster than semihosting. Like 4 orders of magnitude or so.
//!
//! **NOTE** Cortex-M0 chips don't support ITM.
//!
//! You'll have to connect the microcontroller's SWO pin to the SWD interface. Note that some
//! development boards don't provide this option.
//!
//! You'll need [`itmdump`] to receive the message on the host plus you'll need to uncomment two
//! `monitor` commands in the `.gdbinit` file.
//!
//! [`itmdump`]: https://docs.rs/itm/0.2.1/itm/
//!
//! ---

#![no_main]
#![no_std]

use panic_halt as _;

use cortex_m::{iprintln, Peripherals};
use cortex_m_rt::entry;

#[entry]
fn main() -> ! {
    let mut p = Peripherals::take().unwrap();
    let stim = &mut p.ITM.stim[0];

    iprintln!(stim, "Hello, world!");

    loop {}
}

A  => examples/panic.rs +28 -0
@@ 1,28 @@
//! Changing the panicking behavior
//!
//! The easiest way to change the panicking behavior is to use a different [panic handler crate][0].
//!
//! [0]: https://crates.io/keywords/panic-impl

#![no_main]
#![no_std]

// Pick one of these panic handlers:

// `panic!` halts execution; the panic message is ignored
use panic_halt as _;

// Reports panic messages to the host stderr using semihosting
// NOTE to use this you need to uncomment the `panic-semihosting` dependency in Cargo.toml
// use panic_semihosting as _;

// Logs panic messages using the ITM (Instrumentation Trace Macrocell)
// NOTE to use this you need to uncomment the `panic-itm` dependency in Cargo.toml
// use panic_itm as _;

use cortex_m_rt::entry;

#[entry]
fn main() -> ! {
    panic!("Oops")
}

A  => examples/test_on_host.rs +57 -0
@@ 1,57 @@
//! Conditionally compiling tests with std and our executable with no_std.
//!
//! Rust's built in unit testing framework requires the standard library,
//! but we need to build our final executable with no_std.
//! The testing framework also generates a `main` method, so we need to only use the `#[entry]`
//! annotation when building our final image.
//! For more information on why this example works, see this excellent blog post.
//! https://os.phil-opp.com/unit-testing/
//!
//! Running this example:
//!
//! Ensure there are no targets specified under `[build]` in `.cargo/config`
//! In order to make this work, we lose the convenience of having a default target that isn't the
//! host.
//!
//! cargo build --example test_on_host --target thumbv7m-none-eabi
//! cargo test --example test_on_host

#![cfg_attr(test, allow(unused_imports))]

#![cfg_attr(not(test), no_std)]
#![cfg_attr(not(test), no_main)]

// pick a panicking behavior
#[cfg(not(test))]
use panic_halt as _; // you can put a breakpoint on `rust_begin_unwind` to catch panics
// use panic_abort as _; // requires nightly
// use panic_itm as _; // logs messages over ITM; requires ITM support
// use panic_semihosting as _; // logs messages to the host stderr; requires a debugger

use cortex_m::asm;
use cortex_m_rt::entry;

#[cfg(not(test))]
#[entry]
fn main() -> ! {
    asm::nop(); // To not have main optimize to abort in release mode, remove when you add code

    loop {
        // your code goes here
    }
}

fn add(a: i32, b: i32) -> i32 {
    a + b
}

#[cfg(test)]
mod test {
  use super::*;

  #[test]
  fn foo() {
    println!("tests work!");
    assert!(2 == add(1,1));
  }
}

A  => memory.x +34 -0
@@ 1,34 @@
MEMORY
{
  /* NOTE 1 K = 1 KiBi = 1024 bytes */
  /* TODO Adjust these memory regions to match your device memory layout */
  /* These values correspond to the LM3S6965, one of the few devices QEMU can emulate */
  FLASH : ORIGIN = 0x00000000, LENGTH = 256K
  RAM : ORIGIN = 0x20000000, LENGTH = 64K
}

/* This is where the call stack will be allocated. */
/* The stack is of the full descending type. */
/* You may want to use this variable to locate the call stack and static
   variables in different memory regions. Below is shown the default value */
/* _stack_start = ORIGIN(RAM) + LENGTH(RAM); */

/* You can use this symbol to customize the location of the .text section */
/* If omitted the .text section will be placed right after the .vector_table
   section */
/* This is required only on microcontrollers that store some configuration right
   after the vector table */
/* _stext = ORIGIN(FLASH) + 0x400; */

/* Example of putting non-initialized variables into custom RAM locations. */
/* This assumes you have defined a region RAM2 above, and in the Rust
   sources added the attribute `#[link_section = ".ram2bss"]` to the data
   you want to place there. */
/* Note that the section will not be zero-initialized by the runtime! */
/* SECTIONS {
     .ram2bss (NOLOAD) : ALIGN(4) {
       *(.ram2bss);
       . = ALIGN(4);
     } > RAM2
   } INSERT AFTER .bss;
*/

A  => openocd.cfg +12 -0
@@ 1,12 @@
# Sample OpenOCD configuration for the STM32F3DISCOVERY development board

# Depending on the hardware revision you got you'll have to pick ONE of these
# interfaces. At any time only one interface should be commented out.

# Revision C (newer revision)
source [find interface/stlink-v2-1.cfg]

# Revision A and B (older revisions)
# source [find interface/stlink-v2.cfg]

source [find target/stm32f3x.cfg]

A  => openocd.gdb +40 -0
@@ 1,40 @@
target extended-remote :3333

# print demangled symbols
set print asm-demangle on

# set backtrace limit to not have infinite backtrace loops
set backtrace limit 32

# detect unhandled exceptions, hard faults and panics
break DefaultHandler
break HardFault
break rust_begin_unwind
# # run the next few lines so the panic message is printed immediately
# # the number needs to be adjusted for your panic handler
# commands $bpnum
# next 4
# end

# *try* to stop at the user entry point (it might be gone due to inlining)
break main

monitor arm semihosting enable

# # send captured ITM to the file itm.fifo
# # (the microcontroller SWO pin must be connected to the programmer SWO pin)
# # 8000000 must match the core clock frequency
# monitor tpiu config internal itm.txt uart off 8000000

# # OR: make the microcontroller SWO pin output compatible with UART (8N1)
# # 8000000 must match the core clock frequency
# # 2000000 is the frequency of the SWO pin
# monitor tpiu config external uart off 8000000 2000000

# # enable ITM port 0
# monitor itm port 0 on

load

# start the process but immediately halt the processor
stepi

A  => src/main.rs +20 -0
@@ 1,20 @@
#![no_std]
#![no_main]

// pick a panicking behavior
use panic_halt as _; // you can put a breakpoint on `rust_begin_unwind` to catch panics
// use panic_abort as _; // requires nightly
// use panic_itm as _; // logs messages over ITM; requires ITM support
// use panic_semihosting as _; // logs messages to the host stderr; requires a debugger

use cortex_m::asm;
use cortex_m_rt::entry;

#[entry]
fn main() -> ! {
    asm::nop(); // To not have main optimize to abort in release mode, remove when you add code

    loop {
        // your code goes here
    }
}