Add embassy microcontroller example demonstrating async

.github/workflows/build_docs.yaml

@@ -180,7 +180,7 @@ jobs:
                       api/node/docs
                       docs/site
             - name: "Check for docs warnings in internal crates"
-              run: cargo doc --workspace --no-deps --all-features --exclude slint-node --exclude pyslint --exclude mcu-board-support --exclude printerdemo_mcu --exclude carousel --exclude test-* --exclude plotter --exclude uefi-demo --exclude ffmpeg --exclude gstreamer-player --exclude slint-cpp --exclude slint-python
+              run: cargo doc --workspace --no-deps --all-features --exclude slint-node --exclude pyslint --exclude mcu-board-support --exclude mcu-embassy --exclude printerdemo_mcu --exclude carousel --exclude test-* --exclude plotter --exclude uefi-demo --exclude ffmpeg --exclude gstreamer-player --exclude slint-cpp --exclude slint-python
             - name: Clean cache # Don't cache docs to avoid them including removed classes being published
               run: |
                   rm -rf target/doc target/cppdocs api/node/docs

.github/workflows/ci.yaml

@@ -86,12 +86,12 @@ jobs:
                    cargo update -p home --precise 0.5.9
                  fi
             - name: Run tests (not qt)
-              run:  cargo test --verbose --all-features --workspace ${{ matrix.extra_args }} --exclude slint-node --exclude pyslint --exclude test-driver-node --exclude slint-node --exclude test-driver-nodejs --exclude test-driver-cpp --exclude mcu-board-support --exclude printerdemo_mcu --exclude uefi-demo --exclude slint-cpp --exclude slint-python -- --skip=_qt::t
+              run:  cargo test --verbose --all-features --workspace ${{ matrix.extra_args }} --exclude slint-node --exclude pyslint --exclude test-driver-node --exclude slint-node --exclude test-driver-nodejs --exclude test-driver-cpp --exclude mcu-board-support --exclude mcu-embassy --exclude printerdemo_mcu --exclude uefi-demo --exclude slint-cpp --exclude slint-python -- --skip=_qt::t
               env:
                   SLINT_CREATE_SCREENSHOTS: 1
               shell: bash
             - name: Run tests (qt)
-              run: cargo test --verbose --all-features --workspace ${{ matrix.extra_args }} --exclude slint-node --exclude pyslint --exclude test-driver-node --exclude slint-node --exclude test-driver-nodejs --exclude test-driver-cpp --exclude mcu-board-support --exclude printerdemo_mcu --exclude uefi-demo --exclude slint-cpp --exclude slint-python --bin test-driver-rust -- _qt --test-threads=1
+              run: cargo test --verbose --all-features --workspace ${{ matrix.extra_args }} --exclude slint-node --exclude pyslint --exclude test-driver-node --exclude slint-node --exclude test-driver-nodejs --exclude test-driver-cpp --exclude mcu-board-support --exclude mcu-embassy --exclude printerdemo_mcu --exclude uefi-demo --exclude slint-cpp --exclude slint-python --bin test-driver-rust -- _qt --test-threads=1
               shell: bash
             - name: Archive screenshots after failed tests
               if: ${{ failure() }}
@@ -384,6 +384,20 @@ jobs:
             - name: Check
               run: cargo check --target=${{matrix.target}} -p printerdemo_mcu --no-default-features --features=mcu-board-support/${{matrix.feature}} --release
 
+    # test to compile the mcu backend for the arm target (no_std) using embassy
+    mcu-embassy:
+        env:
+            SLINT_FONT_SIZES: 8,11,10,12,13,14,15,16,18,20,22,24,32
+            RUSTFLAGS: --cfg slint_int_coord -D warnings
+            CARGO_PROFILE_DEV_DEBUG: 0
+            CARGO_PROFILE_RELEASE_OPT_LEVEL: s
+        runs-on: ubuntu-22.04
+        steps:
+            - uses: actions/checkout@v4
+            - uses: ./.github/actions/setup-rust
+            - name: Check
+              run: cargo check -p mcu_embassy --bin ui_mcu --target=thumbv8m.main-none-eabihf --no-default-features --features="mcu-embassy/mcu" --release
+
     mcu_esp:
         env:
             RUSTFLAGS: -D warnings

Cargo.toml

@@ -29,6 +29,7 @@ members = [
     'examples/carousel/rust',
     'demos/energy-monitor',
     'demos/home-automation/rust',
+    'examples/mcu-embassy',
     'examples/mcu-board-support',
     'examples/uefi-demo',
     'demos/weather-demo',

examples/mcu-embassy/.cargo/config.toml

@@ -0,0 +1,17 @@
+[target.'cfg(all(target_arch = "arm", target_os = "none"))']
+rustflags = [
+    "-C",
+    "link-arg=--nmagic",
+    "-C",
+    "link-arg=-Tlink.x",
+    "-C",
+    "link-arg=-Tdefmt.x",
+]
+runner = "probe-rs run --chip STM32U5G9ZJTxQ"
+
+[build]
+target = "thumbv8m.main-none-eabihf"
+
+[env]
+DEFMT_LOG = "info"
+RUST_LOG = "info"

examples/mcu-embassy/.vscode/settings.json

@@ -0,0 +1,9 @@
+{
+    // uncomment this to have rust-analyzer work with mcu related code
+    "rust-analyzer.cargo.features": [
+        "mcu",
+        //"simulator",
+    ],
+    "rust-analyzer.check.allTargets": false,
+    "rust-analyzer.showUnlinkedFileNotification": false,
+}

examples/mcu-embassy/Cargo.toml

@@ -0,0 +1,115 @@
+# Copyright © 2025 David Haig
+# SPDX-License-Identifier: MIT
+
+[package]
+name = "mcu-embassy"
+version = "0.1.0"
+edition = "2021"
+authors = ["David Haig <[email protected]>"]
+readme = "README.md"
+license = "MIT"
+resolver = "2"
+publish = false
+repository = "https://github.com/slint-ui/slint"
+homepage = "https://slint.dev"
+
+[dependencies]
+log = "0.4"
+defmt = { version = "0.3", optional = true, features = ["alloc"] }
+defmt-rtt = { version = "0.4", optional = true }
+panic-probe = { version = "0.3", optional = true, features = ["print-defmt"] }
+cortex-m = { version = "0.7.7", optional = true, features = [
+    "inline-asm",
+    "critical-section-single-core",
+] }
+cortex-m-rt = { version = "0.7.3", optional = true }
+slint-generated = { path = "./slint_generated" }
+embedded-alloc = { version = "0.5", optional = true }
+heapless = { version = "0.8", default-features = false, features = [
+    "defmt-03",
+] }
+tinybmp = { version = "0.5" }
+static_cell = { version = "2", optional = true }
+
+#slint = { version = "1.9.1", default-features = false, features = [
+#    "compat-1-2",
+#    "unsafe-single-threaded",
+#    "libm",
+#] }
+
+slint = { path = "../../api/rs/slint", default-features = false, features = [
+    "compat-1-2",
+    "unsafe-single-threaded",
+    "libm",
+] }
+
+embassy-stm32 = { git = "https://github.com/embassy-rs/embassy", rev = "72976fe", optional = true, features = [
+    "stm32u5g9zj",
+    "time-driver-tim2",
+    "exti",
+    "memory-x",
+    "unstable-pac",
+    "chrono",
+    "time",
+    "defmt",
+] }
+embassy-sync = { git = "https://github.com/embassy-rs/embassy", rev = "72976fe" }
+embassy-executor = { git = "https://github.com/embassy-rs/embassy", rev = "72976fe", features = [
+    "task-arena-size-32768",
+    "executor-thread",
+    "integrated-timers",
+] }
+embassy-time = { git = "https://github.com/embassy-rs/embassy", rev = "72976fe" }
+embassy-futures = { git = "https://github.com/embassy-rs/embassy", rev = "72976fe" }
+
+env_logger = { version = "0.9.0", optional = true }
+sdl2 = { git = "https://github.com/Rust-SDL2/rust-sdl2.git", rev = "400e033", optional = true }
+object-pool = { version = "0.6.0", optional = true }
+embedded-hal = { version = "1.0.0", optional = true }
+gt911 = { version = "0.1", features = ["defmt"], optional = true }
+
+[features]
+default = ["mcu"]
+mcu = [
+    "defmt",
+    "defmt-rtt",
+    "panic-probe",
+    "cortex-m",
+    "cortex-m-rt",
+    "embassy-stm32",
+    "embassy-sync/defmt",
+    "embassy-executor/arch-cortex-m",
+    "embassy-executor/executor-interrupt",
+    "embassy-executor/defmt",
+    "embassy-time/tick-hz-32_768",
+    "embassy-time/defmt",
+    "embassy-time/defmt-timestamp-uptime",
+    "embedded-alloc",
+    "embedded-hal",
+    "gt911",
+]
+
+simulator = [
+    "slint/renderer-software",
+    "slint/backend-winit",
+    "slint/std",
+    "embassy-executor/arch-std",
+    "embassy-time/std",
+    "env_logger",
+    "sdl2",
+    "object-pool",
+    "static_cell",
+]
+
+[profile.release]
+debug = true    # required for decent panic messages and log line locations
+opt-level = "s"
+lto = "thin"
+
+[[bin]]
+name = "ui_mcu"
+required-features = ["mcu"]
+
+[[bin]]
+name = "ui_simulator"
+required-features = ["simulator"]

examples/mcu-embassy/README.md

@@ -0,0 +1,88 @@
+# Embassy Slint stm32u5g9j-dk2 Demo
+
+An embedded async Slint GUI demo using Embassy and an stm32u5g9j-dk2 development kit. This demo was written to run on a resource constrained device, not a PC or laptop. 
+The simulator can run on a PC if you do not have the dev kit on hand but it is not meant to be a reference design for an async GUI implementation on a PC.
+
+The stm32u5g9j-dk2 was chosen because of its availability and price point and has enough onboard ram (3MB) and flash (4MB) to run Slint without external psram and flash, reducing setup complexity.
+It comes with a 5" 800x480 IPS touchscreen display. Async is useful for building more complex UIs because you don't have to hand code your own state machines.
+
+Things that are demonstrated here:
+- Sending rendered display buffer to LCD screen asynchronously freeing up the mcu to do other things
+- Responding to hardware events (pressing the USER button on the DK2 changes the colour of the grey circle to blue)
+- Touchscreen actions setting physical hardware (toggling the switch on the touchscreen to turn on the green led on the DK2)
+- Cooperative multitasking (red led continues to flash on a separate task regardless of UI actions)
+- UI animations work
+- The application can be simulated on a PC without having to download to the DK2 every time you want to test something
+
+# Installation instructions
+
+Install the cross compilation target for the mcu:
+
+```bash
+ rustup target add thumbv8m.main-none-eabihf
+```
+
+You need software to be able to flash the firmware to the dev kit. 
+
+```bash
+cargo install --force --locked probe-rs-tools
+```
+
+# Running the application
+
+Plug a usbc cable into the ST-LINK port on the dk2 and run the following:
+
+```bash
+cargo run --bin ui_mcu --release --features=mcu
+```
+
+Troubleshooting:
+
+If you are getting some complication errors from cortex-m like  "error: invalid register `r1`: unknown register" make sure that you are cross compiling for the correct cpu target:
+
+You can specify the target in the cargo run command in the following file:
+
+In `.cargo/Cargo.toml`
+```toml
+[build]
+target = "thumbv8m.main-none-eabihf"
+```
+
+If using vscode then make sure `rust-analyzer.cargo.features` is set to `mcu` in `.vscode/settings.json`
+
+You may be wondering why you get the following message in the logs: `invalid location: defmt frame-index`
+In the Slint workspace `Cargo.toml` file overrides the `Cargo.toml` file in this crate so make sure the release profile is as follows in that workspace file: 
+```toml
+[profile.release]
+debug = true    # required for decent panic messages and log line locations
+opt-level = "s"
+lto = "thin"
+```
+
+# Running the simulator
+
+Of course you can use Slint's vscode plugin to preview slint files but you may want to actually run your application and simulate the hardware interactions.
+The simulator runs Embassy on the host machine (instead of on an mcu) and renders to the screen using the sdl2 library.
+Hardware like leds and buttons are emulated in the hardware module.
+
+To install SDL2 follow the instructions here: https://github.com/Rust-SDL2/rust-sdl2
+
+To run the simulator:
+```bash
+cargo run --bin ui_simulator --release --features=simulator
+```
+
+
+Troubleshooting:
+
+If you are getting some compilation errors from arrayvec like "error: requires `sized` lang_item" make sure you are NOT targeting the mcu when building for your pc.
+
+Set the target correctly in the command line or comment out the following:
+
+In `.cargo/Cargo.toml`
+```toml
+#[build]
+#target = "thumbv8m.main-none-eabihf"
+```
+
+If using vscode then make sure `rust-analyzer.cargo.features` is set to `simulator` in `.vscode/settings.json`

examples/mcu-embassy/slint_generated/Cargo.toml

@@ -0,0 +1,39 @@
+# Copyright © 2025 David Haig
+# SPDX-License-Identifier: MIT
+
+[package]
+name = "slint-generated"
+version = "0.1.0"
+edition = "2021"
+build = "build.rs"
+authors = ["David Haig <[email protected]>"]
+readme = "README.md"
+resolver = "2"
+license = "MIT"
+publish = false
+repository = "https://github.com/slint-ui/slint"
+homepage = "https://slint.dev"
+
+[dependencies]
+slint = { path = "../../../api/rs/slint", default-features = false, features = [
+    "compat-1-2",
+    "unsafe-single-threaded",
+    "libm",
+    "renderer-software",
+] }
+i-slint-core-macros = { path = "../../../internal/core-macros" }
+
+[build-dependencies]
+slint-build = { path = "../../../api/rs/build" }
+
+#[dependencies]
+#slint = { version = "1.9.1", default-features = false, features = [
+#    "compat-1-2",
+#    "unsafe-single-threaded",
+#    "libm",
+#    "renderer-software",
+#] }
+#i-slint-core-macros = { version = "1.9.1" }
+#
+#[build-dependencies]
+#slint-build = { version = "1.9.1" }

examples/mcu-embassy/slint_generated/README.md

@@ -0,0 +1,3 @@
+# Generated
+
+This crate is here to separate the `.slint` file compilation from the main application.

examples/mcu-embassy/slint_generated/build.rs

@@ -0,0 +1,9 @@
+// Copyright © 2025 David Haig
+// SPDX-License-Identifier: MIT
+
+fn main() {
+    let config = slint_build::CompilerConfiguration::new()
+        .embed_resources(slint_build::EmbedResourcesKind::EmbedForSoftwareRenderer);
+    slint_build::compile_with_config("../ui/main.slint", config).unwrap();
+    slint_build::print_rustc_flags().unwrap();
+}

examples/mcu-embassy/slint_generated/src/lib.rs

@@ -0,0 +1,6 @@
+// Copyright © 2025 David Haig
+// SPDX-License-Identifier: MIT
+
+#![no_std]
+
+slint::include_modules!();