Add embassy-boot

Embassy-boot is a simple bootloader that works together with an
application to provide firmware update capabilities with a minimal risk.

The bootloader consists of a platform-independent part, which implements
the swap algorithm, and a platform-dependent part (currently only for
nRF) that provides addition functionality such as watchdog timers
softdevice support.

examples/boot/src/bin/a.rs

@@ -0,0 +1,49 @@
+#![no_std]
+#![no_main]
+#![macro_use]
+#![feature(generic_associated_types)]
+#![feature(type_alias_impl_trait)]
+
+use embassy_boot_nrf::updater;
+use embassy_nrf::{
+    gpio::{Input, Pull},
+    gpio::{Level, Output, OutputDrive},
+    nvmc::Nvmc,
+    Peripherals,
+};
+use embassy_traits::adapter::BlockingAsync;
+use embedded_hal::digital::v2::InputPin;
+use panic_reset as _;
+
+static APP_B: &[u8] = include_bytes!("../../b.bin");
+
+#[embassy::main]
+async fn main(_s: embassy::executor::Spawner, p: Peripherals) {
+    let mut button = Input::new(p.P0_11, Pull::Up);
+    let mut led = Output::new(p.P0_13, Level::Low, OutputDrive::Standard);
+    //let mut led = Output::new(p.P1_10, Level::Low, OutputDrive::Standard);
+    //let mut button = Input::new(p.P1_02, Pull::Up);
+
+    let nvmc = Nvmc::new(p.NVMC);
+    let mut nvmc = BlockingAsync::new(nvmc);
+
+    loop {
+        button.wait_for_any_edge().await;
+        if button.is_low().unwrap() {
+            let mut updater = updater::new();
+            let mut offset = 0;
+            for chunk in APP_B.chunks(4096) {
+                let mut buf: [u8; 4096] = [0; 4096];
+                buf[..chunk.len()].copy_from_slice(chunk);
+                updater
+                    .write_firmware(offset, &buf, &mut nvmc)
+                    .await
+                    .unwrap();
+                offset += chunk.len();
+            }
+            updater.mark_update(&mut nvmc).await.unwrap();
+            led.set_high();
+            cortex_m::peripheral::SCB::sys_reset();
+        }
+    }
+}

examples/boot/src/bin/b.rs

@@ -0,0 +1,26 @@
+#![no_std]
+#![no_main]
+#![macro_use]
+#![feature(generic_associated_types)]
+#![feature(type_alias_impl_trait)]
+
+use embassy::time::{Duration, Timer};
+use embassy_nrf::{
+    gpio::{Level, Output, OutputDrive},
+    Peripherals,
+};
+
+use panic_reset as _;
+
+#[embassy::main]
+async fn main(_s: embassy::executor::Spawner, p: Peripherals) {
+    let mut led = Output::new(p.P0_13, Level::Low, OutputDrive::Standard);
+    //let mut led = Output::new(p.P1_10, Level::Low, OutputDrive::Standard);
+
+    loop {
+        led.set_high();
+        Timer::after(Duration::from_millis(300)).await;
+        led.set_low();
+        Timer::after(Duration::from_millis(300)).await;
+    }
+}