add defmt-itm

firmware/defmt-itm/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+authors = ["The Knurling-rs developers"]
+categories = ["embedded", "no-std"]
+description = "Transmit defmt log messages over the ITM (Instrumentation Trace Macrocell) stimulus port"
+edition = "2018"
+keywords = ["knurling", "logging", "formatting"]
+license = "MIT OR Apache-2.0"
+name = "defmt-itm"
+readme = "README.md"
+repository = "https://github.com/knurling-rs/defmt"
+version = "0.1.0"
+
+[dependencies]
+cortex-m = "0.6.4"
+defmt = { version = "0.1.2", path = "../.." }

firmware/defmt-itm/README.md

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+# `defmt-itm`
+
+> Transmit [`defmt`] log messages over the ITM (Instrumentation Trace Macrocell) stimulus port 0
+
+[`defmt`]: https://github.com/knurling-rs/defmt
+
+## Support
+
+`defmt-rtt` is part of the [Knurling] project, [Ferrous Systems]' effort at
+improving tooling used to develop for embedded systems.
+
+If you think that our work is useful, consider sponsoring it via [GitHub
+Sponsors].
+
+## License
+
+Licensed under either of
+
+- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
+  http://www.apache.org/licenses/LICENSE-2.0)
+
+- MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
+
+at your option.
+
+### Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
+licensed as above, without any additional terms or conditions.
+
+[Knurling]: https://knurling.ferrous-systems.com/
+[Ferrous Systems]: https://ferrous-systems.com/
+[GitHub Sponsors]: https://github.com/sponsors/knurling-rs

firmware/defmt-itm/src/lib.rs

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+//! [`defmt`](https://github.com/knurling-rs/defmt) global logger over RTT.
+//!
+//! NOTE when using this crate it's not possible to use (link to) the `rtt-target` crate
+//!
+//! To use this crate, link to it by importing it somewhere in your project.
+//!
+//! ```
+//! // src/main.rs or src/bin/my-app.rs
+//! use defmt_rtt as _;
+//! ```
+
+#![no_std]
+
+use core::{
+    ptr::NonNull,
+    sync::atomic::{AtomicBool, Ordering},
+};
+
+use cortex_m::{interrupt, itm, peripheral::ITM, register};
+
+static ENABLED: AtomicBool = AtomicBool::new(false);
+
+/// Enables defmt logging over the ITM stimulus port 0
+pub fn enable(itm: ITM) {
+    // enable stimulus port 0
+    itm.ter[0].write(1);
+    drop(itm);
+    ENABLED.store(true, Ordering::Relaxed);
+}
+
+#[defmt::global_logger]
+struct Logger;
+
+impl defmt::Write for Logger {
+    fn write(&mut self, bytes: &[u8]) {
+        // NOTE(unsafe) this function will be invoked *after* `enable` has run so this crate now has
+        // ownership over the ITM thus it's OK to instantiate the ITM register block here
+        unsafe { itm::write_all(&mut (*ITM::ptr()).stim[0], bytes) }
+    }
+}
+
+static TAKEN: AtomicBool = AtomicBool::new(false);
+static INTERRUPTS_ACTIVE: AtomicBool = AtomicBool::new(false);
+
+unsafe impl defmt::Logger for Logger {
+    fn acquire() -> Option<NonNull<dyn defmt::Write>> {
+        if !ENABLED.load(Ordering::Relaxed) {
+            return None;
+        }
+
+        let primask = register::primask::read();
+        interrupt::disable();
+        if !TAKEN.load(Ordering::Relaxed) {
+            // no need for CAS because interrupts are disabled
+            TAKEN.store(true, Ordering::Relaxed);
+
+            INTERRUPTS_ACTIVE.store(primask.is_active(), Ordering::Relaxed);
+
+            Some(NonNull::from(&Logger as &dyn defmt::Write))
+        } else {
+            if primask.is_active() {
+                // re-enable interrupts
+                unsafe { interrupt::enable() }
+            }
+            None
+        }
+    }
+
+    unsafe fn release(_: NonNull<dyn defmt::Write>) {
+        TAKEN.store(false, Ordering::Relaxed);
+        if INTERRUPTS_ACTIVE.load(Ordering::Relaxed) {
+            // re-enable interrupts
+            interrupt::enable()
+        }
+    }
+}