ferrous-systems · robamu · Jun 4, 2026 · Jun 4, 2026 · Jun 4, 2026 · Jun 4, 2026
diff --git a/training-slides/src/SUMMARY.md b/training-slides/src/SUMMARY.md
@@ -98,6 +98,7 @@ Topics about using Rust on ARM Cortex-M Microcontrollers (and similar). Requires
 * [The Embedded HAL and its implementations](./embedded-hals.md)
 * [Board Support Crates](./board-support.md)
 * [Using defmt](./defmt.md)
+* [async/await](./embedded-async.md)
 
 ## Under development
 

diff --git a/training-slides/src/embedded-async.md b/training-slides/src/embedded-async.md
@@ -0,0 +1,89 @@
+# async/await in Embedded Rust
+
+## Non-blocking programming
+
+- General goal: Offload work to the hardware, and use some mechanism to allow
+  the CPU to do other work while the hardware does the work
+- Interrupts are used to signal progress or completion of an operation
+
+## Model of task contexts
+
+In embedded systems, a generic model of how non-blocking programming works
+often looks like this:
+
+<figure>
+  <img src="images/transaction-non-blocking.drawio.svg">
+</figure>
+
+Note:
+
+- Technically, yielding is optional and you can do busy-waiting to wait
+  for an operation to complete. However, allowing the CPU to do other work is
+  oftentimes the point of non-blocking programming in the first place.
+
+## Mapping to Embedded Rust
+
+- How could this be mapped to Embedded Rust?
+- The general model implies an existence of a scheduler / OS. Do we want
+  a non-blocking ecosystem bound to specific schedulers or operating systems?
+- `async` / `await` provides a language-level solution, which can even be
+  scheduling library independent.
+
+## Async / Await
+
+- Async / Await works by transforming you code into pollable state machines.
+- From a users perspective, you can write code like this
+
+```rust,ignore
+// Some HAL specific constructor.
+let my_async_uart = (...)
+let my_data = &[1, 2, 3, 4];
+let result = my_async_uart.write_all(my_data).await;
+
+let async_delay = Delay;
+async_delay.delay_ms(200).await;
+```
+
+- The CPU can do other work while it is waiting for the UART transfer to complete
+  or the delay to elapse.
+
+Note:
+
+- We assume that the async UART driver was written in a non-blocking way. It would
+  offload work to the hardware, and then detect the completion condition in an
+  interrupt.
+
+## `async` executors
+
+- Embedded specific executors are usually static
+- Popular executors in the Rust ecosystem: RTICv2, embassy
+- Only architecture specific parts that an executor might have: Putting the system to sleep
+  when there is nothing to do.
+
+## Wakers in embedded `async`
+
+- A waker is registered inside the hardware task is started.
+- The task is put to sleep until the waker is called.
+- Inside an interrupt handler, the `wake` method on the waker is called to notify the executor
+  about the completion of an operation.
+
+Note:
+
+- Commonly used waker inside the embedded ecosystem: [`AtomicWaker`](https://docs.rs/futures/latest/futures/task/struct.AtomicWaker.html)
+- Usually, a library will have static instances of that waker, tied to a library provided
+  interrupt handler.
+
+## An `async` UART driver
+
+- We have written an `async` UART driver which can be run with QEMU. An example app using it
+  can be found [here](https://github.com/ferrous-systems/rust-training/blob/main/example-code/qemu-thumbv7em/src/bin/uart_async.rs)
+- The driver can be found [here](https://github.com/ferrous-systems/rust-training/blob/main/example-code/qemu-common/src/cmsdk_uart/asynch.rs)
+
+## Under the hood of `embassy-time`
+
+- `embassy-time` provides a very convenient API. The high-level API for users is also (seemingly)
+  hardware independent. How does this work?
+- We have written an embassy time driver for the simple ARM CMSDK Timer
+  [here](https://github.com/embassy-rs/embassy/blob/main/embassy-time/src/driver_cmsdk/mod.rs)
+- Providing `embassy-time` support boils down to mapping a timekeeper and an scheduling / alarm
+  mechanism to a hardware timer inside a driver and then creating a global instance of that driver.
diff --git a/training-slides/src/images/transaction-non-blocking.drawio b/training-slides/src/images/transaction-non-blocking.drawio
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diff --git a/training-slides/src/images/transaction-non-blocking.drawio.svg b/training-slides/src/images/transaction-non-blocking.drawio.svg