6 files changed, 254 insertions, 26 deletions

diff --git a/embassy-boot/rp/src/lib.rs b/embassy-boot/rp/src/lib.rs
index 25329f9e9..35fc104ec 100644
--- a/embassy-boot/rp/src/lib.rs
+++ b/embassy-boot/rp/src/lib.rs
@@ -6,7 +6,7 @@ mod fmt;
 #[cfg(feature = "nightly")]
 pub use embassy_boot::FirmwareUpdater;
 pub use embassy_boot::{AlignedBuffer, BlockingFirmwareUpdater, BootLoaderConfig, FirmwareUpdaterConfig, State};
-use embassy_rp::flash::{Flash, ERASE_SIZE};
+use embassy_rp::flash::{Blocking, Flash, ERASE_SIZE};
 use embassy_rp::peripherals::{FLASH, WATCHDOG};
 use embassy_rp::watchdog::Watchdog;
 use embassy_time::Duration;
@@ -58,14 +58,14 @@ impl<ACTIVE: NorFlash, DFU: NorFlash, STATE: NorFlash, const BUFFER_SIZE: usize>
 
 /// A flash implementation that will feed a watchdog when touching flash.
 pub struct WatchdogFlash<'d, const SIZE: usize> {
-    flash: Flash<'d, FLASH, SIZE>,
+    flash: Flash<'d, FLASH, Blocking, SIZE>,
     watchdog: Watchdog,
 }
 
 impl<'d, const SIZE: usize> WatchdogFlash<'d, SIZE> {
     /// Start a new watchdog with a given flash and watchdog peripheral and a timeout
     pub fn start(flash: FLASH, watchdog: WATCHDOG, timeout: Duration) -> Self {
-        let flash: Flash<'_, FLASH, SIZE> = Flash::new(flash);
+        let flash = Flash::<_, Blocking, SIZE>::new(flash);
         let mut watchdog = Watchdog::new(watchdog);
         watchdog.start(timeout);
         Self { flash, watchdog }
@@ -73,12 +73,12 @@ impl<'d, const SIZE: usize> WatchdogFlash<'d, SIZE> {
 }
 
 impl<'d, const SIZE: usize> ErrorType for WatchdogFlash<'d, SIZE> {
-    type Error = <Flash<'d, FLASH, SIZE> as ErrorType>::Error;
+    type Error = <Flash<'d, FLASH, Blocking, SIZE> as ErrorType>::Error;
 }
 
 impl<'d, const SIZE: usize> NorFlash for WatchdogFlash<'d, SIZE> {
-    const WRITE_SIZE: usize = <Flash<'d, FLASH, SIZE> as NorFlash>::WRITE_SIZE;
-    const ERASE_SIZE: usize = <Flash<'d, FLASH, SIZE> as NorFlash>::ERASE_SIZE;
+    const WRITE_SIZE: usize = <Flash<'d, FLASH, Blocking, SIZE> as NorFlash>::WRITE_SIZE;
+    const ERASE_SIZE: usize = <Flash<'d, FLASH, Blocking, SIZE> as NorFlash>::ERASE_SIZE;
 
     fn erase(&mut self, from: u32, to: u32) -> Result<(), Self::Error> {
         self.watchdog.feed();
@@ -91,7 +91,7 @@ impl<'d, const SIZE: usize> NorFlash for WatchdogFlash<'d, SIZE> {
 }
 
 impl<'d, const SIZE: usize> ReadNorFlash for WatchdogFlash<'d, SIZE> {
-    const READ_SIZE: usize = <Flash<'d, FLASH, SIZE> as ReadNorFlash>::READ_SIZE;
+    const READ_SIZE: usize = <Flash<'d, FLASH, Blocking, SIZE> as ReadNorFlash>::READ_SIZE;
     fn read(&mut self, offset: u32, data: &mut [u8]) -> Result<(), Self::Error> {
         self.watchdog.feed();
         self.flash.read(offset, data)
diff --git a/embassy-rp/Cargo.toml b/embassy-rp/Cargo.toml
index b53c7a01a..6310ffb62 100644
--- a/embassy-rp/Cargo.toml
+++ b/embassy-rp/Cargo.toml
@@ -48,7 +48,7 @@ boot2-w25x10cl = []
 run-from-ram = []
 
 # Enable nightly-only features
-nightly = ["embedded-hal-1", "embedded-hal-async", "embassy-embedded-hal/nightly", "dep:embassy-usb-driver", "dep:embedded-io"]
+nightly = ["embedded-hal-1", "embedded-hal-async", "embedded-storage-async", "embassy-embedded-hal/nightly", "dep:embassy-usb-driver", "dep:embedded-io"]
 
 # Implement embedded-hal 1.0 alpha traits.
 # Implement embedded-hal-async traits if `nightly` is set as well.
@@ -73,6 +73,7 @@ futures = { version = "0.3.17", default-features = false, features = ["async-awa
 chrono = { version = "0.4", default-features = false, optional = true }
 embedded-io = { version = "0.4.0", features = ["async"], optional = true }
 embedded-storage = { version = "0.3" }
+embedded-storage-async = { version = "0.4.0", optional = true }
 rand_core = "0.6.4"
 fixed = "1.23.1"
 
diff --git a/embassy-rp/src/flash.rs b/embassy-rp/src/flash.rs
index 0ed6808eb..70d867319 100644
--- a/embassy-rp/src/flash.rs
+++ b/embassy-rp/src/flash.rs
@@ -1,11 +1,15 @@
+use core::future::Future;
 use core::marker::PhantomData;
+use core::pin::Pin;
+use core::task::{Context, Poll};
 
-use embassy_hal_internal::Peripheral;
+use embassy_hal_internal::{into_ref, Peripheral, PeripheralRef};
 use embedded_storage::nor_flash::{
     check_erase, check_read, check_write, ErrorType, MultiwriteNorFlash, NorFlash, NorFlashError, NorFlashErrorKind,
     ReadNorFlash,
 };
 
+use crate::dma::{AnyChannel, Channel, Transfer};
 use crate::pac;
 use crate::peripherals::FLASH;
 
@@ -24,6 +28,7 @@ pub const PAGE_SIZE: usize = 256;
 pub const WRITE_SIZE: usize = 1;
 pub const READ_SIZE: usize = 1;
 pub const ERASE_SIZE: usize = 4096;
+pub const ASYNC_READ_SIZE: usize = 4;
 
 /// Error type for NVMC operations.
 #[derive(Debug, Copy, Clone, PartialEq, Eq)]
@@ -57,13 +62,46 @@ impl NorFlashError for Error {
     }
 }
 
-pub struct Flash<'d, T: Instance, const FLASH_SIZE: usize>(PhantomData<&'d mut T>);
+/// Future that waits for completion of a background read
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+pub struct BackgroundRead<'a, 'd, T: Instance, const FLASH_SIZE: usize> {
+    flash: PhantomData<&'a mut Flash<'d, T, Async, FLASH_SIZE>>,
+    transfer: Transfer<'a, AnyChannel>,
+}
 
-impl<'d, T: Instance, const FLASH_SIZE: usize> Flash<'d, T, FLASH_SIZE> {
-    pub fn new(_flash: impl Peripheral<P = T> + 'd) -> Self {
-        Self(PhantomData)
+impl<'a, 'd, T: Instance, const FLASH_SIZE: usize> Future for BackgroundRead<'a, 'd, T, FLASH_SIZE> {
+    type Output = ();
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Pin::new(&mut self.transfer).poll(cx)
     }
+}
 
+impl<'a, 'd, T: Instance, const FLASH_SIZE: usize> Drop for BackgroundRead<'a, 'd, T, FLASH_SIZE> {
+    fn drop(&mut self) {
+        if pac::XIP_CTRL.stream_ctr().read().0 == 0 {
+            return;
+        }
+        pac::XIP_CTRL
+            .stream_ctr()
+            .write_value(pac::xip_ctrl::regs::StreamCtr(0));
+        core::sync::atomic::compiler_fence(core::sync::atomic::Ordering::SeqCst);
+        // Errata RP2040-E8: Perform an uncached read to make sure there's not a transfer in
+        // flight that might effect an address written to start a new transfer.  This stalls
+        // until after any transfer is complete, so the address will not change anymore.
+        const XIP_NOCACHE_NOALLOC_BASE: *const u32 = 0x13000000 as *const _;
+        unsafe {
+            core::ptr::read_volatile(XIP_NOCACHE_NOALLOC_BASE);
+        }
+        core::sync::atomic::compiler_fence(core::sync::atomic::Ordering::SeqCst);
+    }
+}
+
+pub struct Flash<'d, T: Instance, M: Mode, const FLASH_SIZE: usize> {
+    dma: Option<PeripheralRef<'d, AnyChannel>>,
+    phantom: PhantomData<(&'d mut T, M)>,
+}
+
+impl<'d, T: Instance, M: Mode, const FLASH_SIZE: usize> Flash<'d, T, M, FLASH_SIZE> {
     pub fn read(&mut self, offset: u32, bytes: &mut [u8]) -> Result<(), Error> {
         trace!(
             "Reading from 0x{:x} to 0x{:x}",
@@ -182,6 +220,8 @@ impl<'d, T: Instance, const FLASH_SIZE: usize> Flash<'d, T, FLASH_SIZE> {
                 let ch = crate::pac::DMA.ch(n);
                 while ch.read_addr().read() < SRAM_LOWER && ch.ctrl_trig().read().busy() {}
             }
+            // Wait for completion of any background reads
+            while pac::XIP_CTRL.stream_ctr().read().0 > 0 {}
 
             // Run our flash operation in RAM
             operation();
@@ -210,11 +250,73 @@ impl<'d, T: Instance, const FLASH_SIZE: usize> Flash<'d, T, FLASH_SIZE> {
     }
 }
 
-impl<'d, T: Instance, const FLASH_SIZE: usize> ErrorType for Flash<'d, T, FLASH_SIZE> {
+impl<'d, T: Instance, const FLASH_SIZE: usize> Flash<'d, T, Blocking, FLASH_SIZE> {
+    pub fn new(_flash: impl Peripheral<P = T> + 'd) -> Self {
+        Self {
+            dma: None,
+            phantom: PhantomData,
+        }
+    }
+}
+
+impl<'d, T: Instance, const FLASH_SIZE: usize> Flash<'d, T, Async, FLASH_SIZE> {
+    pub fn new(_flash: impl Peripheral<P = T> + 'd, dma: impl Peripheral<P = impl Channel> + 'd) -> Self {
+        into_ref!(dma);
+        Self {
+            dma: Some(dma.map_into()),
+            phantom: PhantomData,
+        }
+    }
+
+    pub fn background_read<'a>(
+        &'a mut self,
+        offset: u32,
+        data: &'a mut [u32],
+    ) -> Result<BackgroundRead<'a, 'd, T, FLASH_SIZE>, Error> {
+        trace!(
+            "Reading in background from 0x{:x} to 0x{:x}",
+            FLASH_BASE as u32 + offset,
+            FLASH_BASE as u32 + offset + (data.len() * 4) as u32
+        );
+        // Can't use check_read because we need to enforce 4-byte alignment
+        let offset = offset as usize;
+        let length = data.len() * 4;
+        if length > self.capacity() || offset > self.capacity() - length {
+            return Err(Error::OutOfBounds);
+        }
+        if offset % 4 != 0 {
+            return Err(Error::Unaligned);
+        }
+
+        while !pac::XIP_CTRL.stat().read().fifo_empty() {
+            pac::XIP_CTRL.stream_fifo().read();
+        }
+
+        pac::XIP_CTRL
+            .stream_addr()
+            .write_value(pac::xip_ctrl::regs::StreamAddr(FLASH_BASE as u32 + offset as u32));
+        pac::XIP_CTRL
+            .stream_ctr()
+            .write_value(pac::xip_ctrl::regs::StreamCtr(data.len() as u32));
+
+        // Use the XIP AUX bus port, rather than the FIFO register access (e.x.
+        // pac::XIP_CTRL.stream_fifo().as_ptr()) to avoid DMA stalling on
+        // general XIP access.
+        const XIP_AUX_BASE: *const u32 = 0x50400000 as *const _;
+        let transfer = unsafe { crate::dma::read(self.dma.as_mut().unwrap(), XIP_AUX_BASE, data, 37) };
+
+        Ok(BackgroundRead {
+            flash: PhantomData,
+            transfer,
+        })
+    }
+}
+
+impl<'d, T: Instance, M: Mode, const FLASH_SIZE: usize> ErrorType for Flash<'d, T, M, FLASH_SIZE> {
     type Error = Error;
 }
 
-impl<'d, T: Instance, const FLASH_SIZE: usize> ReadNorFlash for Flash<'d, T, FLASH_SIZE> {
+impl<'d, T: Instance, M: Mode, const FLASH_SIZE: usize> ReadNorFlash for Flash<'d, T, M, FLASH_SIZE> {
     const READ_SIZE: usize = READ_SIZE;
 
     fn read(&mut self, offset: u32, bytes: &mut [u8]) -> Result<(), Self::Error> {
@@ -226,9 +328,9 @@ impl<'d, T: Instance, const FLASH_SIZE: usize> ReadNorFlash for Flash<'d, T, FLA
     }
 }
 
-impl<'d, T: Instance, const FLASH_SIZE: usize> MultiwriteNorFlash for Flash<'d, T, FLASH_SIZE> {}
+impl<'d, T: Instance, M: Mode, const FLASH_SIZE: usize> MultiwriteNorFlash for Flash<'d, T, M, FLASH_SIZE> {}
 
-impl<'d, T: Instance, const FLASH_SIZE: usize> NorFlash for Flash<'d, T, FLASH_SIZE> {
+impl<'d, T: Instance, M: Mode, const FLASH_SIZE: usize> NorFlash for Flash<'d, T, M, FLASH_SIZE> {
     const WRITE_SIZE: usize = WRITE_SIZE;
 
     const ERASE_SIZE: usize = ERASE_SIZE;
@@ -242,6 +344,74 @@ impl<'d, T: Instance, const FLASH_SIZE: usize> NorFlash for Flash<'d, T, FLASH_S
     }
 }
 
+#[cfg(feature = "nightly")]
+impl<'d, T: Instance, const FLASH_SIZE: usize> embedded_storage_async::nor_flash::ReadNorFlash
+    for Flash<'d, T, Async, FLASH_SIZE>
+{
+    const READ_SIZE: usize = ASYNC_READ_SIZE;
+
+    async fn read(&mut self, offset: u32, bytes: &mut [u8]) -> Result<(), Self::Error> {
+        use core::mem::MaybeUninit;
+
+        // Checked early to simplify address validity checks
+        if bytes.len() % 4 != 0 {
+            return Err(Error::Unaligned);
+        }
+
+        // If the destination address is already aligned, then we can just DMA directly
+        if (bytes.as_ptr() as u32) % 4 == 0 {
+            // Safety: alignment and size have been checked for compatibility
+            let mut buf: &mut [u32] =
+                unsafe { core::slice::from_raw_parts_mut(bytes.as_mut_ptr() as *mut u32, bytes.len() / 4) };
+            self.background_read(offset, &mut buf)?.await;
+            return Ok(());
+        }
+
+        // Destination address is unaligned, so use an intermediate buffer
+        const REALIGN_CHUNK: usize = PAGE_SIZE;
+        // Safety: MaybeUninit requires no initialization
+        let mut buf: [MaybeUninit<u32>; REALIGN_CHUNK / 4] = unsafe { MaybeUninit::uninit().assume_init() };
+        let mut chunk_offset: usize = 0;
+        while chunk_offset < bytes.len() {
+            let chunk_size = (bytes.len() - chunk_offset).min(REALIGN_CHUNK);
+            let buf = &mut buf[..(chunk_size / 4)];
+
+            // Safety: this is written to completely by DMA before any reads
+            let buf = unsafe { &mut *(buf as *mut [MaybeUninit<u32>] as *mut [u32]) };
+            self.background_read(offset + chunk_offset as u32, buf)?.await;
+
+            // Safety: [u8] has more relaxed alignment and size requirements than [u32], so this is just aliasing
+            let buf = unsafe { core::slice::from_raw_parts(buf.as_ptr() as *const _, buf.len() * 4) };
+            bytes[chunk_offset..(chunk_offset + chunk_size)].copy_from_slice(&buf[..chunk_size]);
+
+            chunk_offset += chunk_size;
+        }
+
+        Ok(())
+    }
+
+    fn capacity(&self) -> usize {
+        self.capacity()
+    }
+}
+
+#[cfg(feature = "nightly")]
+impl<'d, T: Instance, const FLASH_SIZE: usize> embedded_storage_async::nor_flash::NorFlash
+    for Flash<'d, T, Async, FLASH_SIZE>
+{
+    const WRITE_SIZE: usize = WRITE_SIZE;
+
+    const ERASE_SIZE: usize = ERASE_SIZE;
+
+    async fn erase(&mut self, from: u32, to: u32) -> Result<(), Self::Error> {
+        self.erase(from, to)
+    }
+
+    async fn write(&mut self, offset: u32, bytes: &[u8]) -> Result<(), Self::Error> {
+        self.write(offset, bytes)
+    }
+}
+
 #[allow(dead_code)]
 mod ram_helpers {
     use core::marker::PhantomData;
@@ -699,9 +869,24 @@ mod ram_helpers {
 
 mod sealed {
     pub trait Instance {}
+    pub trait Mode {}
 }
 
 pub trait Instance: sealed::Instance {}
+pub trait Mode: sealed::Mode {}
 
 impl sealed::Instance for FLASH {}
 impl Instance for FLASH {}
+
+macro_rules! impl_mode {
+    ($name:ident) => {
+        impl sealed::Mode for $name {}
+        impl Mode for $name {}
+    };
+}
+
+pub struct Blocking;
+pub struct Async;
+
+impl_mode!(Blocking);
+impl_mode!(Async);
diff --git a/examples/boot/application/rp/src/bin/a.rs b/examples/boot/application/rp/src/bin/a.rs
index c8497494c..b5e1950cc 100644
--- a/examples/boot/application/rp/src/bin/a.rs
+++ b/examples/boot/application/rp/src/bin/a.rs
@@ -7,7 +7,7 @@ use core::cell::RefCell;
 use defmt_rtt as _;
 use embassy_boot_rp::*;
 use embassy_executor::Spawner;
-use embassy_rp::flash::Flash;
+use embassy_rp::flash::{self, Flash};
 use embassy_rp::gpio::{Level, Output};
 use embassy_rp::watchdog::Watchdog;
 use embassy_sync::blocking_mutex::Mutex;
@@ -34,7 +34,7 @@ async fn main(_s: Spawner) {
     let mut watchdog = Watchdog::new(p.WATCHDOG);
     watchdog.start(Duration::from_secs(8));
 
-    let flash: Flash<_, FLASH_SIZE> = Flash::new(p.FLASH);
+    let flash = Flash::<_, flash::Blocking, FLASH_SIZE>::new(p.FLASH);
     let flash = Mutex::new(RefCell::new(flash));
 
     let config = FirmwareUpdaterConfig::from_linkerfile_blocking(&flash);
diff --git a/examples/rp/src/bin/flash.rs b/examples/rp/src/bin/flash.rs
index 4c4982acc..88bb931d2 100644
--- a/examples/rp/src/bin/flash.rs
+++ b/examples/rp/src/bin/flash.rs
@@ -6,7 +6,7 @@
 
 use defmt::*;
 use embassy_executor::Spawner;
-use embassy_rp::flash::{ERASE_SIZE, FLASH_BASE};
+use embassy_rp::flash::{Async, ERASE_SIZE, FLASH_BASE};
 use embassy_rp::peripherals::FLASH;
 use embassy_time::{Duration, Timer};
 use {defmt_rtt as _, panic_probe as _};
@@ -25,7 +25,7 @@ async fn main(_spawner: Spawner) {
     // https://github.com/knurling-rs/defmt/pull/683
     Timer::after(Duration::from_millis(10)).await;
 
-    let mut flash = embassy_rp::flash::Flash::<_, FLASH_SIZE>::new(p.FLASH);
+    let mut flash = embassy_rp::flash::Flash::<_, Async, FLASH_SIZE>::new(p.FLASH, p.DMA_CH0);
 
     // Get JEDEC id
     let jedec = flash.jedec_id().unwrap();
@@ -40,10 +40,12 @@ async fn main(_spawner: Spawner) {
 
     multiwrite_bytes(&mut flash, ERASE_SIZE as u32);
 
+    background_read(&mut flash, (ERASE_SIZE * 2) as u32).await;
+
     loop {}
 }
 
-fn multiwrite_bytes(flash: &mut embassy_rp::flash::Flash<'_, FLASH, FLASH_SIZE>, offset: u32) {
+fn multiwrite_bytes(flash: &mut embassy_rp::flash::Flash<'_, FLASH, Async, FLASH_SIZE>, offset: u32) {
     info!(">>>> [multiwrite_bytes]");
     let mut read_buf = [0u8; ERASE_SIZE];
     defmt::unwrap!(flash.read(ADDR_OFFSET + offset, &mut read_buf));
@@ -71,7 +73,7 @@ fn multiwrite_bytes(flash: &mut embassy_rp::flash::Flash<'_, FLASH, FLASH_SIZE>,
     }
 }
 
-fn erase_write_sector(flash: &mut embassy_rp::flash::Flash<'_, FLASH, FLASH_SIZE>, offset: u32) {
+fn erase_write_sector(flash: &mut embassy_rp::flash::Flash<'_, FLASH, Async, FLASH_SIZE>, offset: u32) {
     info!(">>>> [erase_write_sector]");
     let mut buf = [0u8; ERASE_SIZE];
     defmt::unwrap!(flash.read(ADDR_OFFSET + offset, &mut buf));
@@ -99,3 +101,35 @@ fn erase_write_sector(flash: &mut embassy_rp::flash::Flash<'_, FLASH, FLASH_SIZE
         defmt::panic!("unexpected");
     }
 }
+
+async fn background_read(flash: &mut embassy_rp::flash::Flash<'_, FLASH, Async, FLASH_SIZE>, offset: u32) {
+    info!(">>>> [background_read]");
+
+    let mut buf = [0u32; 8];
+    defmt::unwrap!(flash.background_read(ADDR_OFFSET + offset, &mut buf)).await;
+
+    info!("Addr of flash block is {:x}", ADDR_OFFSET + offset + FLASH_BASE as u32);
+    info!("Contents start with {=u32:x}", buf[0]);
+
+    defmt::unwrap!(flash.erase(ADDR_OFFSET + offset, ADDR_OFFSET + offset + ERASE_SIZE as u32));
+
+    defmt::unwrap!(flash.background_read(ADDR_OFFSET + offset, &mut buf)).await;
+    info!("Contents after erase starts with {=u32:x}", buf[0]);
+    if buf.iter().any(|x| *x != 0xFFFFFFFF) {
+        defmt::panic!("unexpected");
+    }
+
+    for b in buf.iter_mut() {
+        *b = 0xDABA1234;
+    }
+
+    defmt::unwrap!(flash.write(ADDR_OFFSET + offset, unsafe {
+        core::slice::from_raw_parts(buf.as_ptr() as *const u8, buf.len() * 4)
+    }));
+
+    defmt::unwrap!(flash.background_read(ADDR_OFFSET + offset, &mut buf)).await;
+    info!("Contents after write starts with {=u32:x}", buf[0]);
+    if buf.iter().any(|x| *x != 0xDABA1234) {
+        defmt::panic!("unexpected");
+    }
+}
diff --git a/tests/rp/src/bin/flash.rs b/tests/rp/src/bin/flash.rs
index cf9b86df5..c31d6decf 100644
--- a/tests/rp/src/bin/flash.rs
+++ b/tests/rp/src/bin/flash.rs
@@ -6,11 +6,11 @@ mod common;
 
 use defmt::*;
 use embassy_executor::Spawner;
-use embassy_rp::flash::{ERASE_SIZE, FLASH_BASE};
+use embassy_rp::flash::{Async, ERASE_SIZE, FLASH_BASE};
 use embassy_time::{Duration, Timer};
 use {defmt_rtt as _, panic_probe as _};
 
-const ADDR_OFFSET: u32 = 0x4000;
+const ADDR_OFFSET: u32 = 0x8000;
 
 #[embassy_executor::main]
 async fn main(_spawner: Spawner) {
@@ -23,7 +23,7 @@ async fn main(_spawner: Spawner) {
     // https://github.com/knurling-rs/defmt/pull/683
     Timer::after(Duration::from_millis(10)).await;
 
-    let mut flash = embassy_rp::flash::Flash::<_, { 2 * 1024 * 1024 }>::new(p.FLASH);
+    let mut flash = embassy_rp::flash::Flash::<_, Async, { 2 * 1024 * 1024 }>::new(p.FLASH, p.DMA_CH0);
 
     // Get JEDEC id
     let jedec = defmt::unwrap!(flash.jedec_id());
@@ -60,6 +60,14 @@ async fn main(_spawner: Spawner) {
         defmt::panic!("unexpected");
     }
 
+    let mut buf = [0u32; ERASE_SIZE / 4];
+
+    defmt::unwrap!(flash.background_read(ADDR_OFFSET, &mut buf)).await;
+    info!("Contents after write starts with {=u32:x}", buf[0]);
+    if buf.iter().any(|x| *x != 0xDADADADA) {
+        defmt::panic!("unexpected");
+    }
+
     info!("Test OK");
     cortex_m::asm::bkpt();
 }