init basic examples and setup

examples/embassy-button/Cargo.toml

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+[package]
+name = "embassy-button"
+version = "0.1.0"
+edition = "2024"
+publish = false
+build = "build.rs"
+
+[dependencies]
+cortex-m-rt.workspace = true
+defmt.workspace = true
+defmt-rtt.workspace = true
+embassy-executor = { workspace = true, features = ["defmt", "executor-thread", "platform-cortex-m"] }
+embassy-stm32 = { workspace = true, features = ["defmt", "stm32f103c8", "time-driver-tim2"] }
+embassy-time.workspace = true
+panic-probe.workspace = true

examples/embassy-button/build.rs

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+fn main() {
+    println!("cargo:rerun-if-changed=../../memory.x");
+    println!(
+        "cargo:rustc-link-search={}",
+        std::path::PathBuf::from(std::env::var("CARGO_MANIFEST_DIR").unwrap())
+            .join("../..")
+            .display()
+    );
+}

examples/embassy-button/src/main.rs

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+#![deny(unsafe_code)]
+#![no_std]
+#![no_main]
+
+use defmt::info;
+use defmt_rtt as _;
+use embassy_executor::Spawner;
+use embassy_stm32::gpio::{Input, Level, Output, Pull, Speed};
+use embassy_time::Timer;
+use panic_probe as _;
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let p = embassy_stm32::init(Default::default());
+    let button = Input::new(p.PA0, Pull::Down);
+    let mut led = Output::new(p.PC13, Level::High, Speed::Low);
+    let mut was_pressed = button.is_high();
+
+    info!("embassy-button: polling PA0 every 25 ms");
+
+    loop {
+        let pressed = button.is_high();
+
+        if pressed != was_pressed {
+            was_pressed = pressed;
+
+            if pressed {
+                led.set_low();
+                info!("button pressed");
+            } else {
+                led.set_high();
+                info!("button released");
+            }
+        }
+
+        Timer::after_millis(25).await;
+    }
+}