5 files changed, 277 insertions, 0 deletions

diff --git a/examples/nrf52840-edf/.cargo/config.toml b/examples/nrf52840-edf/.cargo/config.toml
new file mode 100644
index 000000000..e0b9ce59e
--- /dev/null
+++ b/examples/nrf52840-edf/.cargo/config.toml
@@ -0,0 +1,9 @@
+[target.'cfg(all(target_arch = "arm", target_os = "none"))']
+# replace nRF82840_xxAA with your chip as listed in `probe-rs chip list`
+runner = "probe-rs run --chip nRF52840_xxAA"
+
+[build]
+target = "thumbv7em-none-eabi"
+
+[env]
+DEFMT_LOG = "debug"
diff --git a/examples/nrf52840-edf/Cargo.toml b/examples/nrf52840-edf/Cargo.toml
new file mode 100644
index 000000000..1e8803233
--- /dev/null
+++ b/examples/nrf52840-edf/Cargo.toml
@@ -0,0 +1,27 @@
+[package]
+edition = "2021"
+name = "embassy-nrf52840-edf-examples"
+version = "0.1.0"
+license = "MIT OR Apache-2.0"
+publish = false
+
+[dependencies]
+# NOTE: "scheduler-deadline" and "embassy-time-driver" features are enabled
+embassy-executor = { version = "0.9.0", path = "../../embassy-executor", features = ["arch-cortex-m", "executor-thread", "executor-interrupt", "defmt", "scheduler-deadline", "embassy-time-driver"] }
+embassy-time = { version = "0.5.0", path = "../../embassy-time", features = ["defmt", "defmt-timestamp-uptime"] }
+embassy-nrf = { version = "0.7.0", path = "../../embassy-nrf", features = ["defmt", "nrf52840", "time-driver-rtc1", "gpiote", "unstable-pac", "time"] }
+
+defmt = "1.0.1"
+defmt-rtt = "1.0.0"
+
+cortex-m = { version = "0.7.6", features = ["inline-asm", "critical-section-single-core"] }
+cortex-m-rt = "0.7.0"
+panic-probe = { version = "1.0.0", features = ["print-defmt"] }
+
+[profile.release]
+debug = 2
+
+[package.metadata.embassy]
+build = [
+  { target = "thumbv7em-none-eabi", artifact-dir = "out/examples/nrf52840-edf" }
+]
diff --git a/examples/nrf52840-edf/build.rs b/examples/nrf52840-edf/build.rs
new file mode 100644
index 000000000..30691aa97
--- /dev/null
+++ b/examples/nrf52840-edf/build.rs
@@ -0,0 +1,35 @@
+//! This build script copies the `memory.x` file from the crate root into
+//! a directory where the linker can always find it at build time.
+//! For many projects this is optional, as the linker always searches the
+//! project root directory -- wherever `Cargo.toml` is. However, if you
+//! are using a workspace or have a more complicated build setup, this
+//! build script becomes required. Additionally, by requesting that
+//! Cargo re-run the build script whenever `memory.x` is changed,
+//! updating `memory.x` ensures a rebuild of the application with the
+//! new memory settings.
+
+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=-Tdefmt.x");
+}
diff --git a/examples/nrf52840-edf/memory.x b/examples/nrf52840-edf/memory.x
new file mode 100644
index 000000000..15b492bce
--- /dev/null
+++ b/examples/nrf52840-edf/memory.x
@@ -0,0 +1,12 @@
+MEMORY
+{
+  /* NOTE 1 K = 1 KiBi = 1024 bytes */
+  FLASH : ORIGIN = 0x00000000, LENGTH = 1024K
+  RAM : ORIGIN = 0x20000000, LENGTH = 256K
+
+  /* These values correspond to the NRF52840 with Softdevices S140 7.3.0 */
+  /*
+     FLASH : ORIGIN = 0x00027000, LENGTH = 868K
+     RAM : ORIGIN = 0x20020000, LENGTH = 128K
+  */
+}
diff --git a/examples/nrf52840-edf/src/bin/basic.rs b/examples/nrf52840-edf/src/bin/basic.rs
new file mode 100644
index 000000000..d888e17d1
--- /dev/null
+++ b/examples/nrf52840-edf/src/bin/basic.rs
@@ -0,0 +1,194 @@
+//! Basic side-by-side example of the Earliest Deadline First scheduler
+//!
+//! This test spawns a number of background "ambient system load" workers
+//! that are constantly working, and runs two sets of trials.
+//!
+//! The first trial runs with no deadline set, so our trial task is at the
+//! same prioritization level as the background worker tasks.
+//!
+//! The second trial sets a deadline, meaning that it will be given higher
+//! scheduling priority than background tasks, that have no deadline set
+
+#![no_std]
+#![no_main]
+
+use core::sync::atomic::{compiler_fence, Ordering};
+
+use defmt::unwrap;
+use embassy_executor::Spawner;
+use embassy_time::{Duration, Instant, Timer};
+use {defmt_rtt as _, panic_probe as _};
+
+#[embassy_executor::main]
+async fn main(spawner: Spawner) {
+    embassy_nrf::init(Default::default());
+
+    // Enable flash cache to remove some flash latency jitter
+    compiler_fence(Ordering::SeqCst);
+    embassy_nrf::pac::NVMC.icachecnf().write(|w| {
+        w.set_cacheen(true);
+    });
+    compiler_fence(Ordering::SeqCst);
+
+    //
+    // Baseline system load tunables
+    //
+
+    // how many load tasks? More load tasks means more tasks contending
+    // for the runqueue
+    let tasks = 32;
+    // how long should each task work for? The longer the working time,
+    // the longer the max jitter possible, even when a task is prioritized,
+    // as EDF is still cooperative and not pre-emptive
+    //
+    // 33 ticks ~= 1ms
+    let work_time_ticks = 33;
+    // what fraction, 1/denominator, should the system be busy?
+    // bigger number means **less** busy
+    //
+    // 2  => 50%
+    // 4  => 25%
+    // 10 => 10%
+    let denominator = 2;
+
+    // Total time window, so each worker is working 1/denominator
+    // amount of the total time
+    let time_window = work_time_ticks * u64::from(tasks) * denominator;
+
+    // Spawn all of our load workers!
+    for i in 0..tasks {
+        spawner.spawn(unwrap!(load_task(i, work_time_ticks, time_window)));
+    }
+
+    // Let all the tasks spin up
+    defmt::println!("Spinning up load tasks...");
+    Timer::after_secs(1).await;
+
+    //
+    // Trial task worker tunables
+    //
+
+    // How many steps should the workers under test run?
+    // More steps means more chances to have to wait for other tasks
+    // in line ahead of us.
+    let num_steps = 100;
+
+    // How many ticks should the worker take working on each step?
+    //
+    // 33 ticks ~= 1ms
+    let work_ticks = 33;
+    // How many ticks should the worker wait on each step?
+    //
+    // 66 ticks ~= 2ms
+    let idle_ticks = 66;
+
+    // How many times to repeat each trial?
+    let trials = 3;
+
+    // The total time a trial would take, in a perfect unloaded system
+    let theoretical = (num_steps * work_ticks) + (num_steps * idle_ticks);
+
+    defmt::println!("");
+    defmt::println!("Starting UNPRIORITIZED worker trials");
+    for _ in 0..trials {
+        //
+        // UNPRIORITIZED worker
+        //
+        defmt::println!("");
+        defmt::println!("Starting unprioritized worker");
+        let start = Instant::now();
+        for _ in 0..num_steps {
+            let now = Instant::now();
+            while now.elapsed().as_ticks() < work_ticks {}
+            Timer::after_ticks(idle_ticks).await;
+        }
+        let elapsed = start.elapsed().as_ticks();
+        defmt::println!(
+            "Trial complete, theoretical ticks: {=u64}, actual ticks: {=u64}",
+            theoretical,
+            elapsed
+        );
+        let ratio = ((elapsed as f32) / (theoretical as f32)) * 100.0;
+        defmt::println!("Took {=f32}% of ideal time", ratio);
+        Timer::after_millis(500).await;
+    }
+
+    Timer::after_secs(1).await;
+
+    defmt::println!("");
+    defmt::println!("Starting PRIORITIZED worker trials");
+    for _ in 0..trials {
+        //
+        // PRIORITIZED worker
+        //
+        defmt::println!("");
+        defmt::println!("Starting prioritized worker");
+        let start = Instant::now();
+        // Set the deadline to ~2x the theoretical time. In practice, setting any deadline
+        // here elevates the current task above all other worker tasks.
+        let meta = embassy_executor::Metadata::for_current_task().await;
+        meta.set_deadline_after(theoretical * 2);
+
+        // Perform the trial
+        for _ in 0..num_steps {
+            let now = Instant::now();
+            while now.elapsed().as_ticks() < work_ticks {}
+            Timer::after_ticks(idle_ticks).await;
+        }
+
+        let elapsed = start.elapsed().as_ticks();
+        defmt::println!(
+            "Trial complete, theoretical ticks: {=u64}, actual ticks: {=u64}",
+            theoretical,
+            elapsed
+        );
+        let ratio = ((elapsed as f32) / (theoretical as f32)) * 100.0;
+        defmt::println!("Took {=f32}% of ideal time", ratio);
+
+        // Unset the deadline, deadlines are not automatically cleared, and if our
+        // deadline is in the past, then we get very high priority!
+        meta.unset_deadline();
+
+        Timer::after_millis(500).await;
+    }
+
+    defmt::println!("");
+    defmt::println!("Trials Complete.");
+}
+
+#[embassy_executor::task(pool_size = 32)]
+async fn load_task(id: u32, ticks_on: u64, ttl_ticks: u64) {
+    let mut last_print = Instant::now();
+    let mut last_tick = last_print;
+    let mut variance = 0;
+    let mut max_variance = 0;
+    loop {
+        let tgt = last_tick + Duration::from_ticks(ttl_ticks);
+        assert!(tgt > Instant::now(), "fell too behind!");
+
+        Timer::at(tgt).await;
+        let now = Instant::now();
+        // How late are we from the target?
+        let var = now.duration_since(tgt).as_ticks();
+        max_variance = max_variance.max(var);
+        variance += var;
+
+        // blocking work
+        while now.elapsed().as_ticks() < ticks_on {}
+
+        if last_print.elapsed() >= Duration::from_secs(1) {
+            defmt::trace!(
+                "Task {=u32} variance ticks (1s): {=u64}, max: {=u64}, act: {=u64}",
+                id,
+                variance,
+                max_variance,
+                ticks_on,
+            );
+            max_variance = 0;
+            variance = 0;
+            last_print = Instant::now();
+        }
+
+        last_tick = tgt;
+    }
+}