Embedded Rust on IoT devices

Embedded Rust  
On IoT Devices
Lars Gregori 
Hybris Labs

Hybris Labs Prototypes
https://labs.hybris.com/prototype/

Motivation
Functional IoT (http://fpiot.metasepi.org/):
Imagine IoT devices are:
• connected to the internet
• developed in a short time
• storing personal data
• secure
• more intelligence
• inexpensive
Can C design IoT devices like that? No, can't.

Agenda
• Rust Overview
• Embedded Rust
• Cross Compiling
• MCU Debugging

rust-lang.org
Rust is a systems programming language
that runs blazingly fast, prevents segfaults,
and guarantees thread safety.

Rust FAQ
• safe, concurrent, practical system language
• “We do not intend to be  
100% static,  
100% safe,  
100% reflective,  
or too dogmatic in any other sense.”
• Mozilla Servo

Rust FAQ
• multi-paradigm
• OO
• no garbage collection
• strong influences from the world of functional programming
• built on LLVM

Rust FAQ
• Cross-Platform
• Android, iOS, …
• Conditional compilation 
#[cfg(target_os = "macos")]

Rust Overview
Control & Safety

Control & Safety
C/C++
Safety
Control
Haskell
Go
Java
Python

Control & Safety
C/C++
Safety
Control
Haskell
Go
Java
Rust
Python

Rust Concepts
• ownership, the key concept
• borrowing, and their associated feature ‘references’
• lifetimes, an advanced concept of borrowing
‘fighting with the borrow checker’
https://doc.rust-lang.org/book/

Rust Concepts: Ownership
let v = vec![1, 2, 3];
let v2 = v;
// …
println!("v[0] is: {}", v[0]);

let v = vec![1, 2, 3];
let v2 = v;
// …
println!("v[0] is: {}", v[0]); ERROR
use of moved value: `v`

let v = vec![1, 2, 3];
let v2 = v;
take_something(v2);
println!("v[0] is: {}", v[0]); ERROR
use of moved value: `v`

let v = 1;
let v2 = v;
println!("v is: {}", v);

let v = 1;
let v2 = v;
println!("v is: {}", v); OK
Copy Type

fn foo(v1: Vec<i32>, v2: Vec<i32>) -> (Vec<i32>, Vec<i32>, i32) {
// do stuff with v1 and v2
(v1, v2, 42) // hand back ownership, and the result of our function
}
let v1 = vec![1, 2, 3];
let v2 = vec![1, 2, 3];
let (v1, v2, answer) = foo(v1, v2);

Rust Concepts: References and Borrowing
fn foo(v1: &Vec<i32>, v2: &Vec<i32>) -> i32 {
// do stuff with v1 and v2
42 // return the answer
}
let v1 = vec![1, 2, 3];
let v2 = vec![1, 2, 3];
let answer = foo(&v1, &v2);
// we can use v1 and v2 here!

fn foo(v: &Vec<i32>) {
v.push(5);
}
let v = vec![];
foo(&v);

fn foo(v: &Vec<i32>) {
v.push(5);
}
let v = vec![];
foo(&v);
ERROR
cannot borrow immutable borrowed content `*v` as mutable

let mut x = 5;
{
let y = &mut x;
*y += 1;
}
println!("{}", x);
RUN

let mut x = 5;
{
let y = &mut x;
*y += 1;
}
println!("{}", x); OK: 6
RUN

let mut x = 5;
{
let y = &mut x;
*y += 1;
}
println!("{}", x); OK: 6
☜
☜
☟
RUN

The Rules for borrowing:
1. Any borrow must last for a scope no greater than that of the owner.
2. Only one of these kinds of borrows, but not both at the same time:
• one or more references (&T) to a resource
• exactly one mutable reference (&mut T)

let mut x = 5;
let y = &mut x;
*y += 1;
println!("{}", x); Error
RUN
cannot borrow `x` as immutable  
because it is also borrowed as mutable

zinc.rs
Zinc is an experimental attempt to write an ARM stack
that would be similar to CMSIS or mbed in capabilities
but would show rust’s best safety features applied to
embedded development.
Zinc is mostly assembly-free and completely C-free at
the moment.

Rustup
https://www.rustup.rs/
rustup is an installer for the systems programming language Rust
> rustup install nightly-2016-09-17
> rustup override set nightly-2016-09-17

GNU ARM Embedded Toolchain
https://launchpad.net/gcc-arm-embedded/+download
arm-none-eabi-gcc
arm-none-eabi-gdb
…
eabi = Embedded Application Binary Interface (>)

Building
cargo build --target=thumbv7em-none-eabi --features mcu_stm32f4

zinc.rs Issue #336
Failing to build example. #336
src/hal/layout_common.ld
comment out *(.debug_gdb_scripts)

Debugging Rust
> openocd … -c gdb_port 3333
> arm-none-eabi-gdb
(gdb) target remote :3333
(gdb) file ./target/thumbv7em-none-eabi/debug/blink_stm32f4
(gdb) break main
(gdb) continue
(gdb) next

Debugging Rust
(gdb) set delay = 1000
(gdb) list
(gdb) disassemble

What we’ve seen
• Rust Overview ✔
• Embedded Rust ✔
• Cross Compiling ✔
• MCU Debugging ✔
• Hello World

Embedded Rust on IoT devices

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