feat: RGB LED support — blinks green on RX, red on TX

- Added RgbLed trait with impl on () for boards without LED
- Added WS2812 driver (driver/ws2812.rs) using ESP32-S3 RMT peripheral
  - 80MHz clock, 12.5ns resolution, 24-bit GRB encoding
  - Zero extra crate dependencies
- Heltec V3/V3-UART/V4: WS2812B on GPIO38 via RMT channel 0
- RAK WisBlock/Wio Tracker: type LedDriver = (), led = None (no-op)
- Display task: green blink on RX packet, red blink on TX packet
- LED auto-off on timer tick (~1s), off when display is off/reset
- LoRaBoard trait gains type LedDriver: RgbLed associated type
- BoardParts gains led: Option<L> field

src/board/heltec_v3.rs

@@ -7,10 +7,13 @@
 //! For stock (unmodified) V3 boards, use the `heltec_v3_uart` feature instead.
 
 use esp_hal::gpio::{Level, Output, OutputConfig};
+use esp_hal::rmt::{Rmt, TxChannelConfig, TxChannelCreator};
+use esp_hal::time::Rate;
 use static_cell::StaticCell;
 
 use super::esp32s3;
 use super::traits::{BoardParts, LoRaBoard};
+use crate::driver::ws2812::Ws2812;
 use crate::hal::esp32s3 as mcu;
 
 pub use super::esp32s3::{
@@ -18,6 +21,7 @@ pub use super::esp32s3::{
 };
 
 pub type UsbDriver = esp_hal::otg_fs::asynch::Driver<'static>;
+pub type LedDriver = Ws2812;
 
 pub struct UsbParts {
     pub driver: UsbDriver,
@@ -35,6 +39,7 @@ impl LoRaBoard for Board {
     type CommParts = UsbParts;
     type DisplayParts = DisplayParts;
     type DisplayDriver = DisplayDriver;
+    type LedDriver = Ws2812;
 
     fn init() -> Self {
         let p = esp_hal::init(esp_hal::Config::default());
@@ -45,7 +50,7 @@ impl LoRaBoard for Board {
         mcu::mac_address()
     }
 
-    fn into_parts(self) -> BoardParts<RadioParts, UsbParts, DisplayParts> {
+    fn into_parts(self) -> BoardParts<RadioParts, UsbParts, DisplayParts, Ws2812> {
         let p = self.p;
 
         mcu::start_timer(p.TIMG0);
@@ -79,10 +84,20 @@ impl LoRaBoard for Board {
         let i2c = mcu::init_i2c(p.I2C0, p.GPIO17, p.GPIO18);
         let display = Some(DisplayParts { i2c });
 
+        // WS2812B RGB LED on GPIO38 via RMT channel 0
+        let rmt = Rmt::new(p.RMT, Rate::from_mhz(80))
+            .expect("RMT init")
+            .into_async();
+        let led_channel = rmt.channel0
+            .configure_tx(p.GPIO38, TxChannelConfig::default().with_clk_divider(1).with_idle_output(true))
+            .expect("RMT TX channel init");
+        let led = Some(Ws2812::new(led_channel));
+
         BoardParts {
             radio,
             host,
             display,
+            led,
             mac: Self::mac_address(),
         }
     }

src/board/heltec_v3_uart.rs

@@ -7,9 +7,12 @@
 //! use the `heltec_v3` feature instead for native USB CDC-ACM support.
 
 use esp_hal::gpio::{Level, Output, OutputConfig};
+use esp_hal::rmt::{Rmt, TxChannelConfig, TxChannelCreator};
+use esp_hal::time::Rate;
 
 use super::esp32s3;
 use super::traits::{BoardParts, LoRaBoard};
+use crate::driver::ws2812::Ws2812;
 use crate::hal::esp32s3 as mcu;
 
 pub use super::esp32s3::{
@@ -17,6 +20,7 @@ pub use super::esp32s3::{
 };
 
 pub type UartDriver = esp_hal::uart::Uart<'static, esp_hal::Async>;
+pub type LedDriver = Ws2812;
 
 pub struct UartParts {
     pub driver: UartDriver,
@@ -34,6 +38,7 @@ impl LoRaBoard for Board {
     type CommParts = UartParts;
     type DisplayParts = DisplayParts;
     type DisplayDriver = DisplayDriver;
+    type LedDriver = Ws2812;
 
     fn init() -> Self {
         let p = esp_hal::init(esp_hal::Config::default());
@@ -44,7 +49,7 @@ impl LoRaBoard for Board {
         mcu::mac_address()
     }
 
-    fn into_parts(self) -> BoardParts<RadioParts, UartParts, DisplayParts> {
+    fn into_parts(self) -> BoardParts<RadioParts, UartParts, DisplayParts, Ws2812> {
         let p = self.p;
 
         mcu::start_timer(p.TIMG0);
@@ -75,10 +80,20 @@ impl LoRaBoard for Board {
         let i2c = mcu::init_i2c(p.I2C0, p.GPIO17, p.GPIO18);
         let display = Some(DisplayParts { i2c });
 
+        // WS2812B RGB LED on GPIO38 via RMT channel 0
+        let rmt = Rmt::new(p.RMT, Rate::from_mhz(80))
+            .expect("RMT init")
+            .into_async();
+        let led_channel = rmt.channel0
+            .configure_tx(p.GPIO38, TxChannelConfig::default().with_clk_divider(1).with_idle_output(true))
+            .expect("RMT TX channel init");
+        let led = Some(Ws2812::new(led_channel));
+
         BoardParts {
             radio,
             host,
             display,
+            led,
             mac: Self::mac_address(),
         }
     }

src/board/heltec_v4.rs

@@ -1,8 +1,11 @@
 use esp_hal::gpio::{Level, Output, OutputConfig};
+use esp_hal::rmt::{Rmt, TxChannelConfig, TxChannelCreator};
+use esp_hal::time::Rate;
 use static_cell::StaticCell;
 
 use super::esp32s3;
 use super::traits::{BoardParts, LoRaBoard};
+use crate::driver::ws2812::Ws2812;
 use crate::hal::esp32s3 as mcu;
 
 pub use super::esp32s3::{
@@ -11,6 +14,8 @@ pub use super::esp32s3::{
 
 pub type UsbDriver = esp_hal::otg_fs::asynch::Driver<'static>;
 
+pub type LedDriver = Ws2812;
+
 pub struct UsbParts {
     pub driver: UsbDriver,
 }
@@ -27,6 +32,7 @@ impl LoRaBoard for Board {
     type CommParts = UsbParts;
     type DisplayParts = DisplayParts;
     type DisplayDriver = DisplayDriver;
+    type LedDriver = Ws2812;
 
     fn init() -> Self {
         let p = esp_hal::init(esp_hal::Config::default());
@@ -37,7 +43,7 @@ impl LoRaBoard for Board {
         mcu::mac_address()
     }
 
-    fn into_parts(self) -> BoardParts<RadioParts, UsbParts, DisplayParts> {
+    fn into_parts(self) -> BoardParts<RadioParts, UsbParts, DisplayParts, Ws2812> {
         let p = self.p;
 
         mcu::start_timer(p.TIMG0);
@@ -71,10 +77,25 @@ impl LoRaBoard for Board {
         let i2c = mcu::init_i2c(p.I2C0, p.GPIO17, p.GPIO18);
         let display = Some(DisplayParts { i2c });
 
+        // WS2812B RGB LED on GPIO38 via RMT channel 0
+        let rmt = Rmt::new(p.RMT, Rate::from_mhz(80))
+            .expect("RMT init")
+            .into_async();
+        let led_channel = rmt.channel0
+            .configure_tx(
+                p.GPIO38,
+                TxChannelConfig::default()
+                    .with_clk_divider(1)
+                    .with_idle_output(true),
+            )
+            .expect("RMT TX channel init");
+        let led = Some(Ws2812::new(led_channel));
+
         BoardParts {
             radio,
             host,
             display,
+            led,
             mac: Self::mac_address(),
         }
     }

src/board/rak_wisblock_4631.rs

@@ -20,6 +20,7 @@ type RadioSpiDevice = SpiDevice<'static, NoopRawMutex, mcu::SpiBus, Nss>;
 pub type RadioDriver = Sx126x<RadioSpiDevice, Iv, Sx1262>;
 pub type UsbDriver = mcu::UsbNrfDriver;
 pub type DisplayI2c = mcu::I2cBus;
+pub type LedDriver = ();
 
 pub type DisplayDriver = ssd1306::Ssd1306Async<
     ssd1306::prelude::I2CInterface<DisplayI2c>,
@@ -77,6 +78,7 @@ impl LoRaBoard for Board {
     type CommParts = UsbParts;
     type DisplayParts = DisplayParts;
     type DisplayDriver = DisplayDriver;
+    type LedDriver = ();
 
     fn init() -> Self {
         let p = embassy_nrf::init(Default::default());
@@ -87,7 +89,7 @@ impl LoRaBoard for Board {
         mcu::mac_address()
     }
 
-    fn into_parts(self) -> BoardParts<RadioParts, UsbParts, DisplayParts> {
+    fn into_parts(self) -> BoardParts<RadioParts, UsbParts, DisplayParts, ()> {
         let p = self.p;
 
         // ── SPI bus for SX1262 ──────────────────────────────────
@@ -135,6 +137,7 @@ impl LoRaBoard for Board {
             radio,
             host,
             display,
+            led: None,
             mac: Self::mac_address(),
         }
     }

src/board/traits.rs

@@ -1,14 +1,23 @@
 //! Board abstraction trait.
 //!
 //! Every board must implement [`LoRaBoard`] with concrete associated types
-//! for its radio, host communication, and display peripherals. The compiler
-//! enforces completeness — missing types or methods are compile errors.
+//! for its radio, host communication, display, and LED peripherals. The
+//! compiler enforces completeness — missing types or methods are compile errors.
 //!
 //! See `src/board/PORTING.md` for a step-by-step guide to adding a new board.
 
 use embedded_graphics::draw_target::DrawTarget;
 use embedded_graphics::pixelcolor::BinaryColor;
 
+/// Async RGB LED control. Boards without an LED use `()` which is a no-op.
+pub trait RgbLed {
+    fn set_rgb(&mut self, r: u8, g: u8, b: u8) -> impl core::future::Future<Output = ()>;
+}
+
+impl RgbLed for () {
+    async fn set_rgb(&mut self, _r: u8, _g: u8, _b: u8) {}
+}
+
 /// Compile-time contract for a DongLoRa board.
 pub trait LoRaBoard: Sized {
     /// Human-readable board name (shown on display splash screen).
@@ -29,6 +38,9 @@ pub trait LoRaBoard: Sized {
     /// Concrete display driver type (must implement DrawTarget for rendering).
     type DisplayDriver: DrawTarget<Color = BinaryColor>;
 
+    /// RGB LED driver. Boards without an LED use `()`.
+    type LedDriver: RgbLed;
+
     /// Initialize the board hardware.
     fn init() -> Self;
 
@@ -36,13 +48,14 @@ pub trait LoRaBoard: Sized {
     fn mac_address() -> [u8; 6];
 
     /// Decompose initialized board into peripheral bundles for each task.
-    fn into_parts(self) -> BoardParts<Self::RadioParts, Self::CommParts, Self::DisplayParts>;
+    fn into_parts(self) -> BoardParts<Self::RadioParts, Self::CommParts, Self::DisplayParts, Self::LedDriver>;
 }
 
 /// Peripheral bundles for each firmware task, produced by [`LoRaBoard::into_parts`].
-pub struct BoardParts<R, C, D> {
+pub struct BoardParts<R, C, D, L> {
     pub radio: R,
     pub host: C,
     pub display: Option<D>,
+    pub led: Option<L>,
     pub mac: [u8; 6],
 }

src/board/wio_tracker_l1.rs

@@ -20,6 +20,7 @@ type RadioSpiDevice = SpiDevice<'static, NoopRawMutex, mcu::SpiBus, Nss>;
 pub type RadioDriver = Sx126x<RadioSpiDevice, Iv, Sx1262>;
 pub type UsbDriver = mcu::UsbNrfDriver;
 pub type DisplayI2c = mcu::I2cBus;
+pub type LedDriver = ();
 
 pub type DisplayDriver = crate::driver::sh1106::Sh1106<DisplayI2c>;
 
@@ -66,6 +67,7 @@ impl LoRaBoard for Board {
     type CommParts = UsbParts;
     type DisplayParts = DisplayParts;
     type DisplayDriver = DisplayDriver;
+    type LedDriver = ();
 
     fn init() -> Self {
         let mut config = embassy_nrf::config::Config::default();
@@ -79,7 +81,7 @@ impl LoRaBoard for Board {
         mcu::mac_address()
     }
 
-    fn into_parts(self) -> BoardParts<RadioParts, UsbParts, DisplayParts> {
+    fn into_parts(self) -> BoardParts<RadioParts, UsbParts, DisplayParts, ()> {
         let p = self.p;
 
         // ── SPI bus for SX1262 ──────────────────────────────────
@@ -133,6 +135,7 @@ impl LoRaBoard for Board {
             radio,
             host,
             display,
+            led: None,
             mac: Self::mac_address(),
         }
     }