feat: add display UI with splash screen, dashboard, and RSSI sparkline

Implement full SSD1306 OLED display support:
- Splash screen on boot (1.5s) with project name, version, board
- Dashboard showing radio state, config, counters, RSSI/SNR
- RSSI history sparkline (64-sample ring buffer, 2px-wide bars)
- DisplayOn/DisplayOff host commands routed via dedicated channel
- Pure render functions against generic DrawTarget (no hardware coupling)
- Display on/off control bypasses radio task entirely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/critical-section/src/lib.rs

@@ -0,0 +1,308 @@
+#![cfg_attr(not(feature = "std"), no_std)]
+#![doc = include_str!("../README.md")]
+
+mod mutex;
+#[cfg(feature = "std")]
+mod std;
+
+use core::marker::PhantomData;
+
+pub use self::mutex::Mutex;
+
+/// Critical section token.
+///
+/// An instance of this type indicates that the current thread is executing code within a critical
+/// section.
+#[derive(Clone, Copy, Debug)]
+pub struct CriticalSection<'cs> {
+    _private: PhantomData<&'cs ()>,
+
+    // Prevent CriticalSection from being Send or Sync
+    // https://github.com/rust-embedded/critical-section/issues/55
+    _not_send_sync: PhantomData<*mut ()>,
+}
+
+impl<'cs> CriticalSection<'cs> {
+    /// Creates a critical section token.
+    ///
+    /// This method is meant to be used to create safe abstractions rather than being directly used
+    /// in applications.
+    ///
+    /// # Safety
+    ///
+    /// This must only be called when the current thread is in a critical section. The caller must
+    /// ensure that the returned instance will not live beyond the end of the critical section.
+    ///
+    /// The caller must use adequate fences to prevent the compiler from moving the
+    /// instructions inside the critical section to the outside of it. Sequentially consistent fences are
+    /// suggested immediately after entry and immediately before exit from the critical section.
+    ///
+    /// Note that the lifetime `'cs` of the returned instance is unconstrained. User code must not
+    /// be able to influence the lifetime picked for this type, since that might cause it to be
+    /// inferred to `'static`.
+    #[inline(always)]
+    pub unsafe fn new() -> Self {
+        CriticalSection {
+            _private: PhantomData,
+            _not_send_sync: PhantomData,
+        }
+    }
+}
+
+#[cfg(any(
+    all(feature = "restore-state-none", feature = "restore-state-bool"),
+    all(feature = "restore-state-none", feature = "restore-state-u8"),
+    all(feature = "restore-state-none", feature = "restore-state-u16"),
+    all(feature = "restore-state-none", feature = "restore-state-u32"),
+    all(feature = "restore-state-none", feature = "restore-state-u64"),
+    all(feature = "restore-state-bool", feature = "restore-state-u8"),
+    all(feature = "restore-state-bool", feature = "restore-state-u16"),
+    all(feature = "restore-state-bool", feature = "restore-state-u32"),
+    all(feature = "restore-state-bool", feature = "restore-state-u64"),
+    all(feature = "restore-state-bool", feature = "restore-state-usize"),
+    all(feature = "restore-state-u8", feature = "restore-state-u16"),
+    all(feature = "restore-state-u8", feature = "restore-state-u32"),
+    all(feature = "restore-state-u8", feature = "restore-state-u64"),
+    all(feature = "restore-state-u8", feature = "restore-state-usize"),
+    all(feature = "restore-state-u16", feature = "restore-state-u32"),
+    all(feature = "restore-state-u16", feature = "restore-state-u64"),
+    all(feature = "restore-state-u16", feature = "restore-state-usize"),
+    all(feature = "restore-state-u32", feature = "restore-state-u64"),
+    all(feature = "restore-state-u32", feature = "restore-state-usize"),
+    all(feature = "restore-state-u64", feature = "restore-state-usize"),
+))]
+compile_error!("You must set at most one of these Cargo features: restore-state-none, restore-state-bool, restore-state-u8, restore-state-u16, restore-state-u32, restore-state-u64, restore-state-usize");
+
+#[cfg(not(any(
+    feature = "restore-state-bool",
+    feature = "restore-state-u8",
+    feature = "restore-state-u16",
+    feature = "restore-state-u32",
+    feature = "restore-state-u64",
+    feature = "restore-state-usize"
+)))]
+type RawRestoreStateInner = ();
+
+#[cfg(feature = "restore-state-bool")]
+type RawRestoreStateInner = bool;
+
+#[cfg(feature = "restore-state-u8")]
+type RawRestoreStateInner = u8;
+
+#[cfg(feature = "restore-state-u16")]
+type RawRestoreStateInner = u16;
+
+#[cfg(feature = "restore-state-u32")]
+type RawRestoreStateInner = u32;
+
+#[cfg(feature = "restore-state-u64")]
+type RawRestoreStateInner = u64;
+
+#[cfg(feature = "restore-state-usize")]
+type RawRestoreStateInner = usize;
+
+// We have RawRestoreStateInner and RawRestoreState so that we don't have to copypaste the docs 5 times.
+// In the docs this shows as `pub type RawRestoreState = u8` or whatever the selected type is, because
+// the "inner" type alias is private.
+
+/// Raw, transparent "restore state".
+///
+/// This type changes based on which Cargo feature is selected, out of
+/// - `restore-state-none` (default, makes the type be `()`)
+/// - `restore-state-bool`
+/// - `restore-state-u8`
+/// - `restore-state-u16`
+/// - `restore-state-u32`
+/// - `restore-state-u64`
+/// - `restore-state-usize`
+///
+/// See [`RestoreState`].
+///
+/// User code uses [`RestoreState`] opaquely, critical section implementations
+/// use [`RawRestoreState`] so that they can use the inner value.
+pub type RawRestoreState = RawRestoreStateInner;
+
+/// Opaque "restore state".
+///
+/// Implementations use this to "carry over" information between acquiring and releasing
+/// a critical section. For example, when nesting two critical sections of an
+/// implementation that disables interrupts globally, acquiring the inner one won't disable
+/// the interrupts since they're already disabled. The impl would use the restore state to "tell"
+/// the corresponding release that it does *not* have to reenable interrupts yet, only the
+/// outer release should do so.
+///
+/// User code uses [`RestoreState`] opaquely, critical section implementations
+/// use [`RawRestoreState`] so that they can use the inner value.
+#[derive(Clone, Copy, Debug)]
+pub struct RestoreState(RawRestoreState);
+
+impl RestoreState {
+    /// Create an invalid, dummy  `RestoreState`.
+    ///
+    /// This can be useful to avoid `Option` when storing a `RestoreState` in a
+    /// struct field, or a `static`.
+    ///
+    /// Note that due to the safety contract of [`acquire`]/[`release`], you must not pass
+    /// a `RestoreState` obtained from this method to [`release`].
+    pub const fn invalid() -> Self {
+        #[cfg(not(any(
+            feature = "restore-state-bool",
+            feature = "restore-state-u8",
+            feature = "restore-state-u16",
+            feature = "restore-state-u32",
+            feature = "restore-state-u64",
+            feature = "restore-state-usize"
+        )))]
+        return Self(());
+
+        #[cfg(feature = "restore-state-bool")]
+        return Self(false);
+
+        #[cfg(feature = "restore-state-u8")]
+        return Self(0);
+
+        #[cfg(feature = "restore-state-u16")]
+        return Self(0);
+
+        #[cfg(feature = "restore-state-u32")]
+        return Self(0);
+
+        #[cfg(feature = "restore-state-u64")]
+        return Self(0);
+
+        #[cfg(feature = "restore-state-usize")]
+        return Self(0);
+    }
+}
+
+/// Acquire a critical section in the current thread.
+///
+/// This function is extremely low level. Strongly prefer using [`with`] instead.
+///
+/// Nesting critical sections is allowed. The inner critical sections
+/// are mostly no-ops since they're already protected by the outer one.
+///
+/// # Safety
+///
+/// - Each `acquire` call must be paired with exactly one `release` call in the same thread.
+/// - `acquire` returns a "restore state" that you must pass to the corresponding `release` call.
+/// - `acquire`/`release` pairs must be "properly nested", ie it's not OK to do `a=acquire(); b=acquire(); release(a); release(b);`.
+/// - It is UB to call `release` if the critical section is not acquired in the current thread.
+/// - It is UB to call `release` with a "restore state" that does not come from the corresponding `acquire` call.
+/// - It must provide ordering guarantees at least equivalent to a [`core::sync::atomic::Ordering::Acquire`]
+///   on a memory location shared by all critical sections, on which the `release` call will do a
+///   [`core::sync::atomic::Ordering::Release`] operation.
+#[inline(always)]
+pub unsafe fn acquire() -> RestoreState {
+    extern "Rust" {
+        fn _critical_section_1_0_acquire() -> RawRestoreState;
+    }
+
+    #[allow(clippy::unit_arg)]
+    RestoreState(_critical_section_1_0_acquire())
+}
+
+/// Release the critical section.
+///
+/// This function is extremely low level. Strongly prefer using [`with`] instead.
+///
+/// # Safety
+///
+/// See [`acquire`] for the safety contract description.
+#[inline(always)]
+pub unsafe fn release(restore_state: RestoreState) {
+    extern "Rust" {
+        fn _critical_section_1_0_release(restore_state: RawRestoreState);
+    }
+
+    #[allow(clippy::unit_arg)]
+    _critical_section_1_0_release(restore_state.0)
+}
+
+/// Execute closure `f` in a critical section.
+///
+/// Nesting critical sections is allowed. The inner critical sections
+/// are mostly no-ops since they're already protected by the outer one.
+///
+/// # Panics
+///
+/// This function panics if the given closure `f` panics. In this case
+/// the critical section is released before unwinding.
+#[inline]
+pub fn with<R>(f: impl FnOnce(CriticalSection) -> R) -> R {
+    // Helper for making sure `release` is called even if `f` panics.
+    struct Guard {
+        state: RestoreState,
+    }
+
+    impl Drop for Guard {
+        #[inline(always)]
+        fn drop(&mut self) {
+            unsafe { release(self.state) }
+        }
+    }
+
+    let state = unsafe { acquire() };
+    let _guard = Guard { state };
+
+    unsafe { f(CriticalSection::new()) }
+}
+
+/// Methods required for a critical section implementation.
+///
+/// This trait is not intended to be used except when implementing a critical section.
+///
+/// # Safety
+///
+/// Implementations must uphold the contract specified in [`crate::acquire`] and [`crate::release`].
+pub unsafe trait Impl {
+    /// Acquire the critical section.
+    ///
+    /// # Safety
+    ///
+    /// Callers must uphold the contract specified in [`crate::acquire`] and [`crate::release`].
+    unsafe fn acquire() -> RawRestoreState;
+
+    /// Release the critical section.
+    ///
+    /// # Safety
+    ///
+    /// Callers must uphold the contract specified in [`crate::acquire`] and [`crate::release`].
+    unsafe fn release(restore_state: RawRestoreState);
+}
+
+/// Set the critical section implementation.
+///
+/// # Example
+///
+/// ```
+/// # #[cfg(not(feature = "std"))] // needed for `cargo test --features std`
+/// # mod no_std {
+/// use critical_section::RawRestoreState;
+///
+/// struct MyCriticalSection;
+/// critical_section::set_impl!(MyCriticalSection);
+///
+/// unsafe impl critical_section::Impl for MyCriticalSection {
+///     unsafe fn acquire() -> RawRestoreState {
+///         // ...
+///     }
+///
+///     unsafe fn release(restore_state: RawRestoreState) {
+///         // ...
+///     }
+/// }
+/// # }
+#[macro_export]
+macro_rules! set_impl {
+    ($t: ty) => {
+        #[no_mangle]
+        unsafe fn _critical_section_1_0_acquire() -> $crate::RawRestoreState {
+            <$t as $crate::Impl>::acquire()
+        }
+        #[no_mangle]
+        unsafe fn _critical_section_1_0_release(restore_state: $crate::RawRestoreState) {
+            <$t as $crate::Impl>::release(restore_state)
+        }
+    };
+}

vendor/critical-section/src/mutex.rs

@@ -0,0 +1,208 @@
+use super::CriticalSection;
+use core::cell::{Ref, RefCell, RefMut, UnsafeCell};
+
+/// A mutex based on critical sections.
+///
+/// # Example
+///
+/// ```no_run
+/// # use critical_section::Mutex;
+/// # use std::cell::Cell;
+///
+/// static FOO: Mutex<Cell<i32>> = Mutex::new(Cell::new(42));
+///
+/// fn main() {
+///     critical_section::with(|cs| {
+///         FOO.borrow(cs).set(43);
+///     });
+/// }
+///
+/// fn interrupt_handler() {
+///     let _x = critical_section::with(|cs| FOO.borrow(cs).get());
+/// }
+/// ```
+///
+///
+/// # Design
+///
+/// [`std::sync::Mutex`] has two purposes. It converts types that are [`Send`]
+/// but not [`Sync`] into types that are both; and it provides
+/// [interior mutability]. `critical_section::Mutex`, on the other hand, only adds
+/// `Sync`. It does *not* provide interior mutability.
+///
+/// This was a conscious design choice. It is possible to create multiple
+/// [`CriticalSection`] tokens, either by nesting critical sections or `Copy`ing
+/// an existing token. As a result, it would not be sound for [`Mutex::borrow`]
+/// to return `&mut T`, because there would be nothing to prevent calling
+/// `borrow` multiple times to create aliased `&mut T` references.
+///
+/// The solution is to include a runtime check to ensure that each resource is
+/// borrowed only once. This is what `std::sync::Mutex` does. However, this is
+/// a runtime cost that may not be required in all circumstances. For instance,
+/// `Mutex<Cell<T>>` never needs to create `&mut T` or equivalent.
+///
+/// If `&mut T` is needed, the simplest solution is to use `Mutex<RefCell<T>>`,
+/// which is the closest analogy to `std::sync::Mutex`. [`RefCell`] inserts the
+/// exact runtime check necessary to guarantee that the `&mut T` reference is
+/// unique.
+///
+/// To reduce verbosity when using `Mutex<RefCell<T>>`, we reimplement some of
+/// `RefCell`'s methods on it directly.
+///
+/// ```no_run
+/// # use critical_section::Mutex;
+/// # use std::cell::RefCell;
+///
+/// static FOO: Mutex<RefCell<i32>> = Mutex::new(RefCell::new(42));
+///
+/// fn main() {
+///     critical_section::with(|cs| {
+///         // Instead of calling this
+///         let _ = FOO.borrow(cs).take();
+///         // Call this
+///         let _ = FOO.take(cs);
+///         // `RefCell::borrow` and `RefCell::borrow_mut` are renamed to
+///         // `borrow_ref` and `borrow_ref_mut` to avoid name collisions
+///         let _: &mut i32 = &mut *FOO.borrow_ref_mut(cs);
+///     })
+/// }
+/// ```
+///
+/// [`std::sync::Mutex`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html
+/// [interior mutability]: https://doc.rust-lang.org/reference/interior-mutability.html
+#[derive(Debug)]
+pub struct Mutex<T> {
+    // The `UnsafeCell` is not strictly necessary here: In theory, just using `T` should
+    // be fine.
+    // However, without `UnsafeCell`, the compiler may use niches inside `T`, and may
+    // read the niche value _without locking the mutex_. As we don't provide interior
+    // mutability, this is still not violating any aliasing rules and should be perfectly
+    // fine. But as the cost of adding `UnsafeCell` is very small, we add it out of
+    // cautiousness, just in case the reason `T` is not `Sync` in the first place is
+    // something very obscure we didn't consider.
+    inner: UnsafeCell<T>,
+}
+
+impl<T> Mutex<T> {
+    /// Creates a new mutex.
+    #[inline]
+    pub const fn new(value: T) -> Self {
+        Mutex {
+            inner: UnsafeCell::new(value),
+        }
+    }
+
+    /// Gets a mutable reference to the contained value when the mutex is already uniquely borrowed.
+    ///
+    /// This does not require locking or a critical section since it takes `&mut self`, which
+    /// guarantees unique ownership already. Care must be taken when using this method to
+    /// **unsafely** access `static mut` variables, appropriate fences must be used to prevent
+    /// unwanted optimizations.
+    #[inline]
+    pub fn get_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.inner.get() }
+    }
+
+    /// Unwraps the contained value, consuming the mutex.
+    #[inline]
+    pub fn into_inner(self) -> T {
+        self.inner.into_inner()
+    }
+
+    /// Borrows the data for the duration of the critical section.
+    #[inline]
+    pub fn borrow<'cs>(&'cs self, _cs: CriticalSection<'cs>) -> &'cs T {
+        unsafe { &*self.inner.get() }
+    }
+}
+
+impl<T> Mutex<RefCell<T>> {
+    /// Borrow the data and call [`RefCell::replace`]
+    ///
+    /// This is equivalent to `self.borrow(cs).replace(t)`
+    ///
+    /// # Panics
+    ///
+    /// This call could panic. See the documentation for [`RefCell::replace`]
+    /// for more details.
+    #[inline]
+    #[track_caller]
+    pub fn replace<'cs>(&'cs self, cs: CriticalSection<'cs>, t: T) -> T {
+        self.borrow(cs).replace(t)
+    }
+
+    /// Borrow the data and call [`RefCell::replace_with`]
+    ///
+    /// This is equivalent to `self.borrow(cs).replace_with(f)`
+    ///
+    /// # Panics
+    ///
+    /// This call could panic. See the documentation for
+    /// [`RefCell::replace_with`] for more details.
+    #[inline]
+    #[track_caller]
+    pub fn replace_with<'cs, F>(&'cs self, cs: CriticalSection<'cs>, f: F) -> T
+    where
+        F: FnOnce(&mut T) -> T,
+    {
+        self.borrow(cs).replace_with(f)
+    }
+
+    /// Borrow the data and call [`RefCell::borrow`]
+    ///
+    /// This is equivalent to `self.borrow(cs).borrow()`
+    ///
+    /// # Panics
+    ///
+    /// This call could panic. See the documentation for [`RefCell::borrow`]
+    /// for more details.
+    #[inline]
+    #[track_caller]
+    pub fn borrow_ref<'cs>(&'cs self, cs: CriticalSection<'cs>) -> Ref<'cs, T> {
+        self.borrow(cs).borrow()
+    }
+
+    /// Borrow the data and call [`RefCell::borrow_mut`]
+    ///
+    /// This is equivalent to `self.borrow(cs).borrow_mut()`
+    ///
+    /// # Panics
+    ///
+    /// This call could panic. See the documentation for [`RefCell::borrow_mut`]
+    /// for more details.
+    #[inline]
+    #[track_caller]
+    pub fn borrow_ref_mut<'cs>(&'cs self, cs: CriticalSection<'cs>) -> RefMut<'cs, T> {
+        self.borrow(cs).borrow_mut()
+    }
+}
+
+impl<T: Default> Mutex<RefCell<T>> {
+    /// Borrow the data and call [`RefCell::take`]
+    ///
+    /// This is equivalent to `self.borrow(cs).take()`
+    ///
+    /// # Panics
+    ///
+    /// This call could panic. See the documentation for [`RefCell::take`]
+    /// for more details.
+    #[inline]
+    #[track_caller]
+    pub fn take<'cs>(&'cs self, cs: CriticalSection<'cs>) -> T {
+        self.borrow(cs).take()
+    }
+}
+
+// NOTE A `Mutex` can be used as a channel so the protected data must be `Send`
+// to prevent sending non-Sendable stuff (e.g. access tokens) across different
+// threads.
+unsafe impl<T> Sync for Mutex<T> where T: Send {}
+
+/// ``` compile_fail
+/// fn bad(cs: critical_section::CriticalSection) -> &u32 {
+///     let x = critical_section::Mutex::new(42u32);
+///     x.borrow(cs)
+/// }
+/// ```
+#[cfg(doctest)]
+const BorrowMustNotOutliveMutexTest: () = ();

vendor/critical-section/src/std.rs

@@ -0,0 +1,87 @@
+use std::cell::Cell;
+use std::mem::MaybeUninit;
+use std::sync::{Mutex, MutexGuard};
+
+static GLOBAL_MUTEX: Mutex<()> = Mutex::new(());
+
+// This is initialized if a thread has acquired the CS, uninitialized otherwise.
+static mut GLOBAL_GUARD: MaybeUninit<MutexGuard<'static, ()>> = MaybeUninit::uninit();
+
+std::thread_local!(static IS_LOCKED: Cell<bool> = Cell::new(false));
+
+struct StdCriticalSection;
+crate::set_impl!(StdCriticalSection);
+
+unsafe impl crate::Impl for StdCriticalSection {
+    unsafe fn acquire() -> bool {
+        // Allow reentrancy by checking thread local state
+        IS_LOCKED.with(|l| {
+            if l.get() {
+                // CS already acquired in the current thread.
+                return true;
+            }
+
+            // Note: it is fine to set this flag *before* acquiring the mutex because it's thread local.
+            // No other thread can see its value, there's no potential for races.
+            // This way, we hold the mutex for slightly less time.
+            l.set(true);
+
+            // Not acquired in the current thread, acquire it.
+            let guard = match GLOBAL_MUTEX.lock() {
+                Ok(guard) => guard,
+                Err(err) => {
+                    // Ignore poison on the global mutex in case a panic occurred
+                    // while the mutex was held.
+                    err.into_inner()
+                }
+            };
+            GLOBAL_GUARD.write(guard);
+
+            false
+        })
+    }
+
+    unsafe fn release(nested_cs: bool) {
+        if !nested_cs {
+            // SAFETY: As per the acquire/release safety contract, release can only be called
+            // if the critical section is acquired in the current thread,
+            // in which case we know the GLOBAL_GUARD is initialized.
+            //
+            // We have to `assume_init_read` then drop instead of `assume_init_drop` because:
+            // - drop requires exclusive access (&mut) to the contents
+            // - mutex guard drop first unlocks the mutex, then returns. In between those, there's a brief
+            //   moment where the mutex is unlocked but a `&mut` to the contents exists.
+            // - During this moment, another thread can go and use GLOBAL_GUARD, causing `&mut` aliasing.
+            #[allow(let_underscore_lock)]
+            let _ = GLOBAL_GUARD.assume_init_read();
+
+            // Note: it is fine to clear this flag *after* releasing the mutex because it's thread local.
+            // No other thread can see its value, there's no potential for races.
+            // This way, we hold the mutex for slightly less time.
+            IS_LOCKED.with(|l| l.set(false));
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::thread;
+
+    use crate as critical_section;
+
+    #[cfg(feature = "std")]
+    #[test]
+    #[should_panic(expected = "Not a PoisonError!")]
+    fn reusable_after_panic() {
+        let _ = thread::spawn(|| {
+            critical_section::with(|_| {
+                panic!("Boom!");
+            })
+        })
+        .join();
+
+        critical_section::with(|_| {
+            panic!("Not a PoisonError!");
+        })
+    }
+}