rust embedded stm32 stm32ldiscovery stm32l152

Using Rust crates for an STM32 microcontroller board

I'm currently trying to learn Rust (for embedded specifically), coming from a background of C for embedded systems and Python. So far, I've been reading Rust Programming Language and Rust for Embedded, and read a few blog posts on the web.

I want my first project to be a simple "Blinky", where an LED blinks infinitely. I've got an STM32L152CDISCOVERY board with an STM32L152 chip in it (basically same as STM32L151), which is a Cortex M3.

Instead of implementing everything from scratch, I want to leverage existing crates and HALs. I've found two that seem promising: stm32l1 and stm32l1xx-hal. I've tried to read the documentation of each of them and also part of the source code, but I still can't figure out how to use them correctly.

Got a few questions about Rust and about the crates:

I see that stm32l1xx-hal has a dependency on stm32l1. Do I need to add both as a dependency in my Cargo.toml file? Or will that create problems related to ownership?

Is this the correct way to add them? Why is the second one added like that [dependencies.stm32l1]?

[dependencies]
cortex-m-rt = "0.6.10"
cortex-m-semihosting = "0.3.3"
panic-halt = "0.2.0"
stm32l1xx-hal = "0.1.0"

[dependencies.stm32l1]
version = "0.13.0"
features = ["stm32l151", "rt"]

To blink the LD4 (which is connected to ~~PB4~~ PB6), I've got to enable the GPIOB in the RCC register and then configure the pin to push pull output. By inspecting the documentation of stm32l1xx-hal, I see that there is an RCC struct and a PB4 struct with the method into_push_pull_output. However, I still don't understand how to use these structs: how to import them or how to get an instance of them.

I've seen code examples for stm32l1 but not for stm32l1xx-hal. I know that I can do this:

use stm32l1::{stm32l151};
...
let p = stm32l151::Peripherals::take().unwrap();
p.RCC.ahbenr.modify(|_,w| w.gpiopben().set_bit());

But in the source code of stm32l1xx-hal I see that the RCC part is already done in impl GpioExt for $GPIOX, but I don't know how to get to this "Parts" functionality.

Any help that points me in the right direction is appreciated.

Solution

I got some help from a Discord community. The answers were (modified a bit by me):

stm32l1xx-hal already depends on stm32l1 as seen here. There's no need to import it twice. It is enough to add to Cargo.toml:
```
[dependencies.stm32l1xx-hal]
version = "0.1.0"
default-features = false
features = ["stm32l151", "rt"]
```

Note that the default-features = false is optional, but without it the compiler was giving me an error.

The syntaxes are equivalent, but as I said above, I only need to add the HAL one. You can add curly braces {} in the first style to add the options, such as:
```
stm32l1xx-hal = { version = "0.1.0", features = ["stm32l151", "rt"]}
```

The right code for doing the blinky (which was on PB6, not PB4, sigh) was:

#![no_main]
#![no_std]

use panic_halt as _;

use cortex_m_rt::entry;
use stm32l1xx_hal::delay::Delay;
use stm32l1xx_hal::gpio::GpioExt;
use stm32l1xx_hal::hal::digital::v2::OutputPin;
use stm32l1xx_hal::rcc::{Config, RccExt};
use stm32l1xx_hal::stm32::Peripherals;
use stm32l1xx_hal::stm32::CorePeripherals;
use stm32l1xx_hal::time::MicroSeconds;


#[entry]
fn main() -> ! {

    let p = Peripherals::take().unwrap();
    let cp = CorePeripherals::take().unwrap();

    // Get LED pin PB6
    let gpiob = p.GPIOB.split();
    let mut led = gpiob.pb6.into_push_pull_output();

    // Set up a delay
    let rcc = p.RCC.freeze(Config::default());
    let mut delay = Delay::new(cp.SYST, rcc.clocks);

    loop {

        // Turn LED On
        led.set_high().unwrap();

        delay.delay(MicroSeconds(1_000_000_u32));

        // Turn LED Off
        led.set_low().unwrap();

        delay.delay(MicroSeconds(1_000_000_u32));
    }
}

For me, the key was to understand that the split method can be called from the Peripherals because stm32l1xx-hal implemented split for a struct defined in stm32l1. In other words, the HAL crate is not only defining new structs, but also extending functionality for existing structs. I need to wrap my head around trait design patterns.