feat: embassy-boot for rp2040

Add embassy-boot support for RP2040, with examples for the Raspberry Pi
Pico.

Co-authored-by: Mathias Koch <mk@blackbird.online>

examples/boot/bootloader/rp/.cargo/config.toml

@@ -0,0 +1,8 @@
+[target.'cfg(all(target_arch = "arm", target_os = "none"))']
+runner = "probe-run --chip RP2040"
+
+[build]
+target = "thumbv6m-none-eabi"
+
+[env]
+DEFMT_LOG = "trace"

examples/boot/bootloader/rp/Cargo.toml

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+[package]
+edition = "2021"
+name = "rp-bootloader-example"
+version = "0.1.0"
+description = "Example bootloader for RP2040 chips"
+license = "MIT OR Apache-2.0"
+
+[dependencies]
+defmt = { version = "0.3", optional = true }
+defmt-rtt = { version = "0.4", optional = true }
+
+embassy-rp = { path = "../../../../embassy-rp", default-features = false, features = ["nightly"] }
+embassy-boot-rp = { path = "../../../../embassy-boot/rp", default-features = false }
+cortex-m = { version = "0.7.6", features = ["critical-section-single-core"] }
+cortex-m-rt = { version = "0.7" }
+embedded-storage = "0.3.0"
+embedded-storage-async = "0.3.0"
+cfg-if = "1.0.0"
+
+[features]
+defmt = [
+    "dep:defmt",
+    "embassy-boot-rp/defmt",
+    "embassy-rp/defmt",
+]
+debug = ["defmt-rtt", "defmt"]
+
+[profile.release]
+debug = true

examples/boot/bootloader/rp/README.md

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+# Bootloader for RP2040
+
+The bootloader uses `embassy-boot` to interact with the flash.
+
+# Usage
+
+Flashing the bootloader
+
+```
+cargo flash --release --chip RP2040
+```
+
+To debug, use `cargo run` and enable the debug feature flag
+
+``` rust
+cargo run --release --features debug
+```

examples/boot/bootloader/rp/build.rs

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+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");
+
+    println!("cargo:rustc-link-arg-bins=--nmagic");
+    println!("cargo:rustc-link-arg-bins=-Tlink.x");
+    println!("cargo:rustc-link-arg-bins=-Tlink-rp.x");
+    if env::var("CARGO_FEATURE_DEFMT").is_ok() {
+        println!("cargo:rustc-link-arg-bins=-Tdefmt.x");
+    }
+}

examples/boot/bootloader/rp/memory.x

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+MEMORY
+{
+  /* NOTE 1 K = 1 KiBi = 1024 bytes */
+  BOOT2                             : ORIGIN = 0x10000000, LENGTH = 0x100
+  FLASH                             : ORIGIN = 0x10000100, LENGTH = 24K
+  BOOTLOADER_STATE                  : ORIGIN = 0x10006000, LENGTH = 4K
+  ACTIVE                            : ORIGIN = 0x10007000, LENGTH = 512K
+  DFU                               : ORIGIN = 0x10087000, LENGTH = 516K
+  RAM                               : ORIGIN = 0x20000000, LENGTH = 256K
+}
+
+__bootloader_state_start = ORIGIN(BOOTLOADER_STATE) - ORIGIN(BOOT2);
+__bootloader_state_end = ORIGIN(BOOTLOADER_STATE) + LENGTH(BOOTLOADER_STATE) - ORIGIN(BOOT2);
+
+__bootloader_active_start = ORIGIN(ACTIVE) - ORIGIN(BOOT2);
+__bootloader_active_end = ORIGIN(ACTIVE) + LENGTH(ACTIVE) - ORIGIN(BOOT2);
+
+__bootloader_dfu_start = ORIGIN(DFU) - ORIGIN(BOOT2);
+__bootloader_dfu_end = ORIGIN(DFU) + LENGTH(DFU) - ORIGIN(BOOT2);

examples/boot/bootloader/rp/src/main.rs

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+#![no_std]
+#![no_main]
+
+use cortex_m_rt::{entry, exception};
+#[cfg(feature = "defmt")]
+use defmt_rtt as _;
+use embassy_boot_rp::*;
+use embassy_rp::flash::{Flash, ERASE_SIZE};
+use embassy_rp::peripherals::FLASH;
+
+const FLASH_SIZE: usize = 2 * 1024 * 1024;
+
+#[entry]
+fn main() -> ! {
+    let p = embassy_rp::init(Default::default());
+
+    // Uncomment this if you are debugging the bootloader with debugger/RTT attached,
+    // as it prevents a hard fault when accessing flash 'too early' after boot.
+    /*
+    for i in 0..10000000 {
+        cortex_m::asm::nop();
+    }
+    */
+
+    let mut bl: BootLoader = BootLoader::default();
+    let flash: Flash<'_, FLASH, FLASH_SIZE> = Flash::new(p.FLASH);
+    let mut flash = BootFlash::<_, ERASE_SIZE>::new(flash);
+    let start = bl.prepare(&mut SingleFlashConfig::new(&mut flash));
+    core::mem::drop(flash);
+
+    unsafe { bl.load(start) }
+}
+
+#[no_mangle]
+#[cfg_attr(target_os = "none", link_section = ".HardFault.user")]
+unsafe extern "C" fn HardFault() {
+    cortex_m::peripheral::SCB::sys_reset();
+}
+
+#[exception]
+unsafe fn DefaultHandler(_: i16) -> ! {
+    const SCB_ICSR: *const u32 = 0xE000_ED04 as *const u32;
+    let irqn = core::ptr::read_volatile(SCB_ICSR) as u8 as i16 - 16;
+
+    panic!("DefaultHandler #{:?}", irqn);
+}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    cortex_m::asm::udf();
+}