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.

embassy-boot/boot/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+authors = [
+    "Ulf Lilleengen <lulf@redhat.com>",
+]
+edition = "2018"
+name = "embassy-boot"
+version = "0.1.0"
+description = "Bootloader using Embassy"
+
+[lib]
+
+[dependencies]
+defmt = { version = "0.3", optional = true }
+log = { version = "0.4", optional = true  }
+embassy = { path = "../../embassy", default-features = false }
+embedded-storage = "0.3.0"
+embedded-storage-async = "0.3.0"
+
+[dev-dependencies]
+log = "0.4"
+env_logger = "0.9"
+rand = "0.8"
+futures = { version = "0.3", features = ["executor"] }

embassy-boot/boot/src/fmt.rs

@@ -0,0 +1,225 @@
+#![macro_use]
+#![allow(unused_macros)]
+
+#[cfg(all(feature = "defmt", feature = "log"))]
+compile_error!("You may not enable both `defmt` and `log` features.");
+
+macro_rules! assert {
+    ($($x:tt)*) => {
+        {
+            #[cfg(not(feature = "defmt"))]
+            ::core::assert!($($x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::assert!($($x)*);
+        }
+    };
+}
+
+macro_rules! assert_eq {
+    ($($x:tt)*) => {
+        {
+            #[cfg(not(feature = "defmt"))]
+            ::core::assert_eq!($($x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::assert_eq!($($x)*);
+        }
+    };
+}
+
+macro_rules! assert_ne {
+    ($($x:tt)*) => {
+        {
+            #[cfg(not(feature = "defmt"))]
+            ::core::assert_ne!($($x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::assert_ne!($($x)*);
+        }
+    };
+}
+
+macro_rules! debug_assert {
+    ($($x:tt)*) => {
+        {
+            #[cfg(not(feature = "defmt"))]
+            ::core::debug_assert!($($x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::debug_assert!($($x)*);
+        }
+    };
+}
+
+macro_rules! debug_assert_eq {
+    ($($x:tt)*) => {
+        {
+            #[cfg(not(feature = "defmt"))]
+            ::core::debug_assert_eq!($($x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::debug_assert_eq!($($x)*);
+        }
+    };
+}
+
+macro_rules! debug_assert_ne {
+    ($($x:tt)*) => {
+        {
+            #[cfg(not(feature = "defmt"))]
+            ::core::debug_assert_ne!($($x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::debug_assert_ne!($($x)*);
+        }
+    };
+}
+
+macro_rules! todo {
+    ($($x:tt)*) => {
+        {
+            #[cfg(not(feature = "defmt"))]
+            ::core::todo!($($x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::todo!($($x)*);
+        }
+    };
+}
+
+macro_rules! unreachable {
+    ($($x:tt)*) => {
+        {
+            #[cfg(not(feature = "defmt"))]
+            ::core::unreachable!($($x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::unreachable!($($x)*);
+        }
+    };
+}
+
+macro_rules! panic {
+    ($($x:tt)*) => {
+        {
+            #[cfg(not(feature = "defmt"))]
+            ::core::panic!($($x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::panic!($($x)*);
+        }
+    };
+}
+
+macro_rules! trace {
+    ($s:literal $(, $x:expr)* $(,)?) => {
+        {
+            #[cfg(feature = "log")]
+            ::log::trace!($s $(, $x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::trace!($s $(, $x)*);
+            #[cfg(not(any(feature = "log", feature="defmt")))]
+            let _ = ($( & $x ),*);
+        }
+    };
+}
+
+macro_rules! debug {
+    ($s:literal $(, $x:expr)* $(,)?) => {
+        {
+            #[cfg(feature = "log")]
+            ::log::debug!($s $(, $x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::debug!($s $(, $x)*);
+            #[cfg(not(any(feature = "log", feature="defmt")))]
+            let _ = ($( & $x ),*);
+        }
+    };
+}
+
+macro_rules! info {
+    ($s:literal $(, $x:expr)* $(,)?) => {
+        {
+            #[cfg(feature = "log")]
+            ::log::info!($s $(, $x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::info!($s $(, $x)*);
+            #[cfg(not(any(feature = "log", feature="defmt")))]
+            let _ = ($( & $x ),*);
+        }
+    };
+}
+
+macro_rules! warn {
+    ($s:literal $(, $x:expr)* $(,)?) => {
+        {
+            #[cfg(feature = "log")]
+            ::log::warn!($s $(, $x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::warn!($s $(, $x)*);
+            #[cfg(not(any(feature = "log", feature="defmt")))]
+            let _ = ($( & $x ),*);
+        }
+    };
+}
+
+macro_rules! error {
+    ($s:literal $(, $x:expr)* $(,)?) => {
+        {
+            #[cfg(feature = "log")]
+            ::log::error!($s $(, $x)*);
+            #[cfg(feature = "defmt")]
+            ::defmt::error!($s $(, $x)*);
+            #[cfg(not(any(feature = "log", feature="defmt")))]
+            let _ = ($( & $x ),*);
+        }
+    };
+}
+
+#[cfg(feature = "defmt")]
+macro_rules! unwrap {
+    ($($x:tt)*) => {
+        ::defmt::unwrap!($($x)*)
+    };
+}
+
+#[cfg(not(feature = "defmt"))]
+macro_rules! unwrap {
+    ($arg:expr) => {
+        match $crate::fmt::Try::into_result($arg) {
+            ::core::result::Result::Ok(t) => t,
+            ::core::result::Result::Err(e) => {
+                ::core::panic!("unwrap of `{}` failed: {:?}", ::core::stringify!($arg), e);
+            }
+        }
+    };
+    ($arg:expr, $($msg:expr),+ $(,)? ) => {
+        match $crate::fmt::Try::into_result($arg) {
+            ::core::result::Result::Ok(t) => t,
+            ::core::result::Result::Err(e) => {
+                ::core::panic!("unwrap of `{}` failed: {}: {:?}", ::core::stringify!($arg), ::core::format_args!($($msg,)*), e);
+            }
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub struct NoneError;
+
+pub trait Try {
+    type Ok;
+    type Error;
+    fn into_result(self) -> Result<Self::Ok, Self::Error>;
+}
+
+impl<T> Try for Option<T> {
+    type Ok = T;
+    type Error = NoneError;
+
+    #[inline]
+    fn into_result(self) -> Result<T, NoneError> {
+        self.ok_or(NoneError)
+    }
+}
+
+impl<T, E> Try for Result<T, E> {
+    type Ok = T;
+    type Error = E;
+
+    #[inline]
+    fn into_result(self) -> Self {
+        self
+    }
+}

embassy-boot/boot/src/lib.rs

@@ -0,0 +1,550 @@
+#![feature(type_alias_impl_trait)]
+#![feature(generic_associated_types)]
+#![no_std]
+///! embassy-boot is a bootloader and firmware updater for embedded devices with flash
+///! storage implemented using embedded-storage
+///!
+///! The bootloader works in conjunction with the firmware application, and only has the
+///! ability to manage two flash banks with an active and a updatable part. It implements
+///! a swap algorithm that is power-failure safe, and allows reverting to the previous
+///! version of the firmware, should the application crash and fail to mark itself as booted.
+///!
+///! This library is intended to be used by platform-specific bootloaders, such as embassy-boot-nrf,
+///! which defines the limits and flash type for that particular platform.
+///!
+mod fmt;
+
+use embedded_storage::nor_flash::{NorFlash, ReadNorFlash};
+use embedded_storage_async::nor_flash::AsyncNorFlash;
+
+pub const BOOT_MAGIC: u32 = 0xD00DF00D;
+pub const SWAP_MAGIC: u32 = 0xF00FDAAD;
+
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub struct Partition {
+    pub from: usize,
+    pub to: usize,
+}
+
+impl Partition {
+    pub const fn new(from: usize, to: usize) -> Self {
+        Self { from, to }
+    }
+    pub const fn len(&self) -> usize {
+        self.to - self.from
+    }
+}
+
+#[derive(PartialEq, Debug)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub enum State {
+    Boot,
+    Swap,
+}
+
+#[derive(PartialEq, Debug)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub enum BootError<E> {
+    Flash(E),
+    BadMagic,
+}
+
+impl<E> From<E> for BootError<E> {
+    fn from(error: E) -> Self {
+        BootError::Flash(error)
+    }
+}
+
+/// BootLoader works with any flash implementing embedded_storage and can also work with
+/// different page sizes.
+pub struct BootLoader<const PAGE_SIZE: usize> {
+    // Page with current state of bootloader. The state partition has the following format:
+    // | Range    | Description                                                                                        |
+    // | 0 - 4    | Magic indicating bootloader state. BOOT_MAGIC means boot, SWAP_MAGIC means swap. |
+    // | 4 - N    | Progress index used while swapping or reverting                                                    |
+    state: Partition,
+    // Location of the partition which will be booted from
+    active: Partition,
+    // Location of the partition which will be swapped in when requested
+    dfu: Partition,
+}
+
+impl<const PAGE_SIZE: usize> BootLoader<PAGE_SIZE> {
+    pub fn new(active: Partition, dfu: Partition, state: Partition) -> Self {
+        assert_eq!(active.len() % PAGE_SIZE, 0);
+        assert_eq!(dfu.len() % PAGE_SIZE, 0);
+        // DFU partition must have an extra page
+        assert!(dfu.len() - active.len() >= PAGE_SIZE);
+        // Ensure we have enough progress pages to store copy progress
+        assert!(active.len() / PAGE_SIZE >= (state.len() - 4) / PAGE_SIZE);
+        Self { active, dfu, state }
+    }
+
+    pub fn boot_address(&self) -> usize {
+        self.active.from
+    }
+
+    /// Perform necessary boot preparations like swapping images.
+    ///
+    /// The DFU partition is assumed to be 1 page bigger than the active partition for the swap
+    /// algorithm to work correctly.
+    ///
+    /// SWAPPING
+    ///
+    /// Assume a flash size of 3 pages for the active partition, and 4 pages for the DFU partition.
+    /// The swap index contains the copy progress, as to allow continuation of the copy process on
+    /// power failure. The index counter is represented within 1 or more pages (depending on total
+    /// flash size), where a page X is considered swapped if index at location (X + WRITE_SIZE)
+    /// contains a zero value. This ensures that index updates can be performed atomically and
+    /// avoid a situation where the wrong index value is set (page write size is "atomic").
+    ///
+    /// +-----------+------------+--------+--------+--------+--------+
+    /// | Partition | Swap Index | Page 0 | Page 1 | Page 3 | Page 4 |
+    /// +-----------+------------+--------+--------+--------+--------+
+    /// |    Active |          0 |      1 |      2 |      3 |      - |
+    /// |       DFU |          0 |      3 |      2 |      1 |      X |
+    /// +-----------+-------+--------+--------+--------+--------+
+    ///
+    /// The algorithm starts by copying 'backwards', and after the first step, the layout is
+    /// as follows:
+    ///
+    /// +-----------+------------+--------+--------+--------+--------+
+    /// | Partition | Swap Index | Page 0 | Page 1 | Page 3 | Page 4 |
+    /// +-----------+------------+--------+--------+--------+--------+
+    /// |    Active |          1 |      1 |      2 |      1 |      - |
+    /// |       DFU |          1 |      3 |      2 |      1 |      3 |
+    /// +-----------+------------+--------+--------+--------+--------+
+    ///
+    /// The next iteration performs the same steps
+    ///
+    /// +-----------+------------+--------+--------+--------+--------+
+    /// | Partition | Swap Index | Page 0 | Page 1 | Page 3 | Page 4 |
+    /// +-----------+------------+--------+--------+--------+--------+
+    /// |    Active |          2 |      1 |      2 |      1 |      - |
+    /// |       DFU |          2 |      3 |      2 |      2 |      3 |
+    /// +-----------+------------+--------+--------+--------+--------+
+    ///
+    /// And again until we're done
+    ///
+    /// +-----------+------------+--------+--------+--------+--------+
+    /// | Partition | Swap Index | Page 0 | Page 1 | Page 3 | Page 4 |
+    /// +-----------+------------+--------+--------+--------+--------+
+    /// |    Active |          3 |      3 |      2 |      1 |      - |
+    /// |       DFU |          3 |      3 |      1 |      2 |      3 |
+    /// +-----------+------------+--------+--------+--------+--------+
+    ///
+    /// REVERTING
+    ///
+    /// The reverting algorithm uses the swap index to discover that images were swapped, but that
+    /// the application failed to mark the boot successful. In this case, the revert algorithm will
+    /// run.
+    ///
+    /// The revert index is located separately from the swap index, to ensure that revert can continue
+    /// on power failure.
+    ///
+    /// The revert algorithm works forwards, by starting copying into the 'unused' DFU page at the start.
+    ///
+    /// +-----------+--------------+--------+--------+--------+--------+
+    /// | Partition | Revert Index | Page 0 | Page 1 | Page 3 | Page 4 |
+    //*/
+    /// +-----------+--------------+--------+--------+--------+--------+
+    /// |    Active |            3 |      1 |      2 |      1 |      - |
+    /// |       DFU |            3 |      3 |      1 |      2 |      3 |
+    /// +-----------+--------------+--------+--------+--------+--------+
+    ///
+    ///
+    /// +-----------+--------------+--------+--------+--------+--------+
+    /// | Partition | Revert Index | Page 0 | Page 1 | Page 3 | Page 4 |
+    /// +-----------+--------------+--------+--------+--------+--------+
+    /// |    Active |            3 |      1 |      2 |      1 |      - |
+    /// |       DFU |            3 |      3 |      2 |      2 |      3 |
+    /// +-----------+--------------+--------+--------+--------+--------+
+    ///
+    /// +-----------+--------------+--------+--------+--------+--------+
+    /// | Partition | Revert Index | Page 0 | Page 1 | Page 3 | Page 4 |
+    /// +-----------+--------------+--------+--------+--------+--------+
+    /// |    Active |            3 |      1 |      2 |      3 |      - |
+    /// |       DFU |            3 |      3 |      2 |      1 |      3 |
+    /// +-----------+--------------+--------+--------+--------+--------+
+    ///
+    pub fn prepare_boot<F: NorFlash + ReadNorFlash>(
+        &mut self,
+        flash: &mut F,
+    ) -> Result<State, BootError<F::Error>> {
+        // Copy contents from partition N to active
+        let state = self.read_state(flash)?;
+        match state {
+            State::Swap => {
+                //
+                // Check if we already swapped. If we're in the swap state, this means we should revert
+                // since the app has failed to mark boot as successful
+                //
+                if !self.is_swapped(flash)? {
+                    trace!("Swapping");
+                    self.swap(flash)?;
+                } else {
+                    trace!("Reverting");
+                    self.revert(flash)?;
+
+                    // Overwrite magic and reset progress
+                    flash.write(self.state.from as u32, &[0, 0, 0, 0])?;
+                    flash.erase(self.state.from as u32, self.state.to as u32)?;
+                    flash.write(self.state.from as u32, &BOOT_MAGIC.to_le_bytes())?;
+                }
+            }
+            _ => {}
+        }
+        Ok(state)
+    }
+
+    fn is_swapped<F: ReadNorFlash>(&mut self, flash: &mut F) -> Result<bool, F::Error> {
+        let page_count = self.active.len() / PAGE_SIZE;
+        let progress = self.current_progress(flash)?;
+
+        Ok(progress >= page_count * 2)
+    }
+
+    fn current_progress<F: ReadNorFlash>(&mut self, flash: &mut F) -> Result<usize, F::Error> {
+        let max_index = ((self.state.len() - 4) / 4) - 1;
+        for i in 0..max_index {
+            let mut buf: [u8; 4] = [0; 4];
+            flash.read((self.state.from + 4 + i * 4) as u32, &mut buf)?;
+            if buf == [0xFF, 0xFF, 0xFF, 0xFF] {
+                return Ok(i);
+            }
+        }
+        Ok(max_index)
+    }
+
+    fn update_progress<F: NorFlash>(&mut self, idx: usize, flash: &mut F) -> Result<(), F::Error> {
+        let w = self.state.from + 4 + idx * 4;
+        flash.write(w as u32, &[0, 0, 0, 0])?;
+        Ok(())
+    }
+
+    fn active_addr(&self, n: usize) -> usize {
+        self.active.from + n * PAGE_SIZE
+    }
+
+    fn dfu_addr(&self, n: usize) -> usize {
+        self.dfu.from + n * PAGE_SIZE
+    }
+
+    fn copy_page_once<F: NorFlash + ReadNorFlash>(
+        &mut self,
+        idx: usize,
+        from: usize,
+        to: usize,
+        flash: &mut F,
+    ) -> Result<(), F::Error> {
+        let mut buf: [u8; PAGE_SIZE] = [0; PAGE_SIZE];
+        if self.current_progress(flash)? <= idx {
+            flash.read(from as u32, &mut buf)?;
+            flash.erase(to as u32, (to + PAGE_SIZE) as u32)?;
+            flash.write(to as u32, &buf)?;
+            self.update_progress(idx, flash)?;
+        }
+        Ok(())
+    }
+
+    fn swap<F: NorFlash + ReadNorFlash>(&mut self, flash: &mut F) -> Result<(), F::Error> {
+        let page_count = self.active.len() / PAGE_SIZE;
+        // trace!("Page count: {}", page_count);
+        for page in 0..page_count {
+            // Copy active page to the 'next' DFU page.
+            let active_page = self.active_addr(page_count - 1 - page);
+            let dfu_page = self.dfu_addr(page_count - page);
+            // info!("Copy active {} to dfu {}", active_page, dfu_page);
+            self.copy_page_once(page * 2, active_page, dfu_page, flash)?;
+
+            // Copy DFU page to the active page
+            let active_page = self.active_addr(page_count - 1 - page);
+            let dfu_page = self.dfu_addr(page_count - 1 - page);
+            //info!("Copy dfy {} to active {}", dfu_page, active_page);
+            self.copy_page_once(page * 2 + 1, dfu_page, active_page, flash)?;
+        }
+
+        Ok(())
+    }
+
+    fn revert<F: NorFlash + ReadNorFlash>(&mut self, flash: &mut F) -> Result<(), F::Error> {
+        let page_count = self.active.len() / PAGE_SIZE;
+        for page in 0..page_count {
+            // Copy the bad active page to the DFU page
+            let active_page = self.active_addr(page);
+            let dfu_page = self.dfu_addr(page);
+            self.copy_page_once(page_count * 2 + page * 2, active_page, dfu_page, flash)?;
+
+            // Copy the DFU page back to the active page
+            let active_page = self.active_addr(page);
+            let dfu_page = self.dfu_addr(page + 1);
+            self.copy_page_once(page_count * 2 + page * 2 + 1, dfu_page, active_page, flash)?;
+        }
+
+        Ok(())
+    }
+
+    fn read_state<F: ReadNorFlash>(&mut self, flash: &mut F) -> Result<State, BootError<F::Error>> {
+        let mut magic: [u8; 4] = [0; 4];
+        flash.read(self.state.from as u32, &mut magic)?;
+
+        match u32::from_le_bytes(magic) {
+            SWAP_MAGIC => Ok(State::Swap),
+            _ => Ok(State::Boot),
+        }
+    }
+}
+
+/// FirmwareUpdater is an application API for interacting with the BootLoader without the ability to
+/// 'mess up' the internal bootloader state
+pub struct FirmwareUpdater {
+    state: Partition,
+    dfu: Partition,
+}
+
+impl FirmwareUpdater {
+    pub const fn new(dfu: Partition, state: Partition) -> Self {
+        Self { dfu, state }
+    }
+
+    /// Return the length of the DFU area
+    pub fn firmware_len(&self) -> usize {
+        self.dfu.len()
+    }
+
+    /// Instruct bootloader that DFU should commence at next boot.
+    pub async fn mark_update<F: AsyncNorFlash>(&mut self, flash: &mut F) -> Result<(), F::Error> {
+        flash.write(self.state.from as u32, &[0, 0, 0, 0]).await?;
+        flash
+            .erase(self.state.from as u32, self.state.to as u32)
+            .await?;
+        info!(
+            "Setting swap magic at {} to 0x{:x}, LE: 0x{:x}",
+            self.state.from,
+            &SWAP_MAGIC,
+            &SWAP_MAGIC.to_le_bytes()
+        );
+        flash
+            .write(self.state.from as u32, &SWAP_MAGIC.to_le_bytes())
+            .await?;
+        Ok(())
+    }
+
+    /// Mark firmware boot successfully
+    pub async fn mark_booted<F: AsyncNorFlash>(&mut self, flash: &mut F) -> Result<(), F::Error> {
+        flash.write(self.state.from as u32, &[0, 0, 0, 0]).await?;
+        flash
+            .erase(self.state.from as u32, self.state.to as u32)
+            .await?;
+        flash
+            .write(self.state.from as u32, &BOOT_MAGIC.to_le_bytes())
+            .await?;
+        Ok(())
+    }
+
+    // Write to a region of the DFU page
+    pub async fn write_firmware<F: AsyncNorFlash>(
+        &mut self,
+        offset: usize,
+        data: &[u8],
+        flash: &mut F,
+    ) -> Result<(), F::Error> {
+        info!(
+            "Writing firmware at offset 0x{:x} len {}",
+            self.dfu.from + offset,
+            data.len()
+        );
+
+        flash
+            .erase(
+                (self.dfu.from + offset) as u32,
+                (self.dfu.from + offset + data.len()) as u32,
+            )
+            .await?;
+        flash.write((self.dfu.from + offset) as u32, data).await
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use core::convert::Infallible;
+    use core::future::Future;
+    use embedded_storage_async::nor_flash::AsyncReadNorFlash;
+    use futures::executor::block_on;
+
+    const STATE: Partition = Partition::new(0, 4096);
+    const ACTIVE: Partition = Partition::new(4096, 61440);
+    const DFU: Partition = Partition::new(61440, 122880);
+
+    #[test]
+    fn test_bad_magic() {
+        let mut flash = MemFlash([0xff; 131072]);
+
+        let mut bootloader = BootLoader::<4096>::new(ACTIVE, DFU, STATE);
+
+        assert_eq!(
+            bootloader.prepare_boot(&mut flash),
+            Err(BootError::BadMagic)
+        );
+    }
+
+    #[test]
+    fn test_boot_state() {
+        let mut flash = MemFlash([0xff; 131072]);
+        flash.0[0..4].copy_from_slice(&BOOT_MAGIC.to_le_bytes());
+
+        let mut bootloader = BootLoader::<4096>::new(ACTIVE, DFU, STATE);
+
+        assert_eq!(State::Boot, bootloader.prepare_boot(&mut flash).unwrap());
+    }
+
+    #[test]
+    fn test_swap_state() {
+        env_logger::init();
+        let mut flash = MemFlash([0xff; 131072]);
+
+        let original: [u8; ACTIVE.len()] = [rand::random::<u8>(); ACTIVE.len()];
+        let update: [u8; DFU.len()] = [rand::random::<u8>(); DFU.len()];
+
+        for i in ACTIVE.from..ACTIVE.to {
+            flash.0[i] = original[i - ACTIVE.from];
+        }
+
+        let mut bootloader = BootLoader::<4096>::new(ACTIVE, DFU, STATE);
+        let mut updater = FirmwareUpdater::new(DFU, STATE);
+        for i in (DFU.from..DFU.to).step_by(4) {
+            let base = i - DFU.from;
+            let data: [u8; 4] = [
+                update[base],
+                update[base + 1],
+                update[base + 2],
+                update[base + 3],
+            ];
+            block_on(updater.write_firmware(i - DFU.from, &data, &mut flash)).unwrap();
+        }
+        block_on(updater.mark_update(&mut flash)).unwrap();
+
+        assert_eq!(State::Swap, bootloader.prepare_boot(&mut flash).unwrap());
+
+        for i in ACTIVE.from..ACTIVE.to {
+            assert_eq!(flash.0[i], update[i - ACTIVE.from], "Index {}", i);
+        }
+
+        // First DFU page is untouched
+        for i in DFU.from + 4096..DFU.to {
+            assert_eq!(flash.0[i], original[i - DFU.from - 4096], "Index {}", i);
+        }
+
+        // Running again should cause a revert
+        assert_eq!(State::Swap, bootloader.prepare_boot(&mut flash).unwrap());
+
+        for i in ACTIVE.from..ACTIVE.to {
+            assert_eq!(flash.0[i], original[i - ACTIVE.from], "Index {}", i);
+        }
+
+        // Last page is untouched
+        for i in DFU.from..DFU.to - 4096 {
+            assert_eq!(flash.0[i], update[i - DFU.from], "Index {}", i);
+        }
+
+        // Mark as booted
+        block_on(updater.mark_booted(&mut flash)).unwrap();
+        assert_eq!(State::Boot, bootloader.prepare_boot(&mut flash).unwrap());
+    }
+
+    struct MemFlash([u8; 131072]);
+
+    impl NorFlash for MemFlash {
+        const WRITE_SIZE: usize = 4;
+        const ERASE_SIZE: usize = 4096;
+        fn erase(&mut self, from: u32, to: u32) -> Result<(), Self::Error> {
+            let from = from as usize;
+            let to = to as usize;
+            for i in from..to {
+                self.0[i] = 0xFF;
+                self.0[i] = 0xFF;
+                self.0[i] = 0xFF;
+                self.0[i] = 0xFF;
+            }
+            Ok(())
+        }
+
+        fn write(&mut self, offset: u32, data: &[u8]) -> Result<(), Self::Error> {
+            assert!(data.len() % 4 == 0);
+            assert!(offset % 4 == 0);
+            assert!(offset as usize + data.len() < 131072);
+
+            self.0[offset as usize..offset as usize + data.len()].copy_from_slice(data);
+
+            Ok(())
+        }
+    }
+
+    impl ReadNorFlash for MemFlash {
+        const READ_SIZE: usize = 4;
+        type Error = Infallible;
+
+        fn read(&mut self, offset: u32, buf: &mut [u8]) -> Result<(), Self::Error> {
+            let len = buf.len();
+            buf[..].copy_from_slice(&self.0[offset as usize..offset as usize + len]);
+            Ok(())
+        }
+
+        fn capacity(&self) -> usize {
+            131072
+        }
+    }
+
+    impl AsyncReadNorFlash for MemFlash {
+        const READ_SIZE: usize = 4;
+        type Error = Infallible;
+
+        type ReadFuture<'a> = impl Future<Output = Result<(), Self::Error>> + 'a;
+        fn read<'a>(&'a mut self, offset: usize, buf: &'a mut [u8]) -> Self::ReadFuture<'a> {
+            async move {
+                let len = buf.len();
+                buf[..].copy_from_slice(&self.0[offset as usize..offset as usize + len]);
+                Ok(())
+            }
+        }
+
+        fn capacity(&self) -> usize {
+            131072
+        }
+    }
+
+    impl AsyncNorFlash for MemFlash {
+        const WRITE_SIZE: usize = 4;
+        const ERASE_SIZE: usize = 4096;
+
+        type EraseFuture<'a> = impl Future<Output = Result<(), Self::Error>> + 'a;
+        fn erase<'a>(&'a mut self, from: u32, to: u32) -> Self::EraseFuture<'a> {
+            async move {
+                let from = from as usize;
+                let to = to as usize;
+                for i in from..to {
+                    self.0[i] = 0xFF;
+                    self.0[i] = 0xFF;
+                    self.0[i] = 0xFF;
+                    self.0[i] = 0xFF;
+                }
+                Ok(())
+            }
+        }
+
+        type WriteFuture<'a> = impl Future<Output = Result<(), Self::Error>> + 'a;
+        fn write<'a>(&'a mut self, offset: u32, data: &'a [u8]) -> Self::WriteFuture<'a> {
+            async move {
+                assert!(data.len() % 4 == 0);
+                assert!(offset % 4 == 0);
+                assert!(offset as usize + data.len() < 131072);
+
+                self.0[offset as usize..offset as usize + data.len()].copy_from_slice(data);
+
+                Ok(())
+            }
+        }
+    }
+}