feat(t114): add Heltec Mesh Node T114 board support

Adds nRF52840 + SX1262 + 1.14" 240×135 ST7789 color TFT support. First
color display board in the project; introduces a BoardDisplay trait so
each board renders to its native pixel format and resolution without
aliasing or color-quantization round-trips.

Architecture:
- New BoardDisplay trait (src/display.rs) bundles render_*, present(),
  set_bright/set_dim. Replaces the old DrawTarget<Color=BinaryColor>
  + DisplayBrightness combo as the LoRaBoard::DisplayDriver bound.
- Mono OLED drivers (Sh1106, Ssd1306Async) get adapter impls that
  delegate to the existing display::render module — no behavior change
  for any existing board.
- T114 ST7789 driver (src/driver/st7789.rs) wraps lcd-async (async fork
  of mipidsi) with a 64,800-byte raw byte framebuffer in .bss. Renders
  via lcd_async::raw_framebuf::RawFrameBuf<Rgb565, _>, presents via a
  single async DMA blit (panel.show_raw_data(...).await) — the await
  yields the executor for the ~65 ms SPI transfer so the radio task
  isn't starved during repaints.
- PWM backlight on PWM0 / P0.15 (active-LOW, inverted polarity) for
  smooth dim/bright transitions instead of GPIO toggle.
- Native 240×135 Rgb565 renderer (src/display/render_color.rs) with
  splash + dashboard + sparkline.
- Shared QR-code blit (src/display/qr.rs), generic over PixelColor,
  re-centers the 64×64 bitmap which has cells in cols 0..50 and ~14 px
  of right-side padding — both mono and color splash now show the QR
  with 7 px quiet zones on all four sides (was visibly left-shifted).
- Shared content types (BoardInfo, DashboardCtx) decouple what to draw
  from how each board renders it.
- create_display() now takes the board's full DisplayParts bundle
  (was just the I2C bus) so non-I2C displays can carry SPI + control
  pins through.

Hardware:
- VEXT_ENABLE on P0.21 driven HIGH at boot — powers the SX1262 + TFT
  rail. Without this, lora-phy init succeeds at the SPI level but
  TX_DONE never fires.
- VTFT_CTRL on P0.03, active LOW; backlight on P0.15, active LOW.
- TFT SPI2 (SCK P1.08 / MOSI P1.09) at 8 MHz over EasyDMA. Async
  ExclusiveDevice from embedded-hal-bus (with the 'async' feature).
- lcd-async builder at display_size(135, 240), display_offset(52, 40),
  Deg90 rotation, ColorInversion::Inverted — standard 1.14" ST7789
  die mapping.
- Linker: shared ld/nrf52840-memory.x (S140 SoftDevice preserved at
  0x01000-0x26000 per project policy).

src/board/PORTING.md

@@ -70,8 +70,10 @@ impl LoRaBoard for Board {
 ### 5. Add display init
 
 ```rust
-pub async fn create_display(i2c: DisplayI2c) -> Option<DisplayDriver> {
-    // Construct and initialize your display driver (SSD1306, SH1106, etc.)
+pub async fn create_display(parts: DisplayParts) -> Option<DisplayDriver> {
+    // Construct and initialize your display driver (SSD1306, SH1106,
+    // ST7789, etc.) using whatever pins/buses you bundled into
+    // DisplayParts in `into_parts()`.
 }
 ```
 

src/board/elecrow_thinknode_m2.rs

@@ -48,8 +48,8 @@ pub struct DisplayParts {
 
 // ── Display init ────────────────────────────────────────────────────
 
-pub async fn create_display(i2c: DisplayI2c) -> Option<DisplayDriver> {
-    let mut display = Sh1106::new(i2c, 0x3C);
+pub async fn create_display(parts: DisplayParts) -> Option<DisplayDriver> {
+    let mut display = Sh1106::new(parts.i2c, 0x3C);
 
     embassy_time::Timer::after_millis(100).await;
     if display.init().await.is_err() {

src/board/esp32.rs

@@ -47,13 +47,13 @@ pub type DisplayDriver = ssd1306::Ssd1306Async<
 >;
 
 /// Construct and initialize an SSD1306 display from raw I²C.
-pub async fn create_display(i2c: DisplayI2c) -> Option<DisplayDriver> {
+pub async fn create_display(parts: DisplayParts) -> Option<DisplayDriver> {
     use ssd1306::mode::DisplayConfigAsync;
     use ssd1306::prelude::{Brightness, DisplayRotation};
     use ssd1306::size::DisplaySize128x64;
     use ssd1306::{I2CDisplayInterface, Ssd1306Async};
 
-    let interface = I2CDisplayInterface::new(i2c);
+    let interface = I2CDisplayInterface::new(parts.i2c);
     let mut display = Ssd1306Async::new(interface, DisplaySize128x64, DisplayRotation::Rotate0)
         .into_buffered_graphics_mode();
 

src/board/esp32s3.rs

@@ -63,13 +63,13 @@ pub type DisplayDriver = ssd1306::Ssd1306Async<
     feature = "heltec_v3_uart",
     feature = "heltec_v4"
 ))]
-pub async fn create_display(i2c: DisplayI2c) -> Option<DisplayDriver> {
+pub async fn create_display(parts: DisplayParts) -> Option<DisplayDriver> {
     use ssd1306::mode::DisplayConfigAsync;
     use ssd1306::prelude::{Brightness, DisplayRotation};
     use ssd1306::size::DisplaySize128x64;
     use ssd1306::{I2CDisplayInterface, Ssd1306Async};
 
-    let interface = I2CDisplayInterface::new(i2c);
+    let interface = I2CDisplayInterface::new(parts.i2c);
     let mut display = Ssd1306Async::new(interface, DisplaySize128x64, DisplayRotation::Rotate0)
         .into_buffered_graphics_mode();
 

src/board/heltec_mesh_node_t114.rs

@@ -0,0 +1,285 @@
+//! Heltec Mesh Node T114 (nRF52840 + SX1262 + 1.14" ST7789 TFT).
+//!
+//! Hardware reference: cross-verified across MeshCore, Meshtastic, and
+//! RNode firmwares. Pin maps quoted from
+//! `meshcore-spec/references/MeshCore/variants/heltec_t114/variant.h` and
+//! `meshtastic/firmware/variants/nrf52840/heltec_mesh_node_t114/variant.h`.
+//!
+//! Stage 2: panel comes up with static colors via the `St7789Color`
+//! driver. Stage 3 swaps in the proper color renderer module.
+
+use embassy_embedded_hal::shared_bus::asynch::spi::SpiDevice;
+use embassy_nrf::gpio::{Input, Level, Output, OutputDrive, Pull};
+use embassy_nrf::pwm::{Prescaler, SimpleConfig, SimplePwm};
+use embassy_nrf::spim::{self, Spim};
+use embassy_nrf::usb::Driver;
+use embassy_sync::blocking_mutex::raw::NoopRawMutex;
+use embassy_time::{Delay, Timer};
+
+use embedded_hal_bus::spi::ExclusiveDevice;
+use lcd_async::interface::SpiInterface;
+use lcd_async::models::ST7789;
+use lcd_async::options::{ColorInversion, Orientation, Rotation};
+use lora_phy::iv::GenericSx126xInterfaceVariant;
+use lora_phy::sx126x::{self, Sx1262, Sx126x};
+use static_cell::ConstStaticCell;
+
+use super::traits::{BoardParts, LoRaBoard};
+use crate::driver::inverted_pin::InvertedPin;
+use crate::driver::simple_led::SimpleLed;
+use crate::driver::st7789::{St7789Color, FB_BYTES};
+use crate::hal::nrf52840 as mcu;
+
+// ── Concrete peripheral types ───────────────────────────────────────
+
+type Nss = Output<'static>;
+type Iv = GenericSx126xInterfaceVariant<Output<'static>, Input<'static>>;
+type RadioSpiDevice = SpiDevice<'static, NoopRawMutex, mcu::SpiBus, Nss>;
+pub type RadioDriver = Sx126x<RadioSpiDevice, Iv, Sx1262>;
+pub type UsbDriver = mcu::UsbNrfDriver;
+// Green LED on P1.03, active LOW.
+pub type LedDriver = SimpleLed<InvertedPin<Output<'static>>>;
+
+// ── TFT bus and driver type aliases ─────────────────────────────────
+
+type TftSpim = Spim<'static>;
+type TftSpiDevice = ExclusiveDevice<TftSpim, Output<'static>, Delay>;
+type TftInterface = SpiInterface<TftSpiDevice, Output<'static>>;
+pub type DisplayDriver = St7789Color<TftInterface, Output<'static>>;
+
+// ── Peripheral bundles ──────────────────────────────────────────────
+
+pub struct RadioParts {
+    pub driver: RadioDriver,
+    pub delay: Delay,
+}
+
+pub struct UsbParts {
+    pub driver: UsbDriver,
+}
+
+/// Assembled-but-not-yet-initialized TFT plumbing. Real initialization
+/// (power gate, RST cycle, mipidsi init) happens in `create_display`.
+pub struct DisplayParts {
+    interface: TftInterface,
+    rst_pin: Output<'static>,
+    vdd_en: Output<'static>,
+    backlight: SimplePwm<'static>,
+}
+
+// ── Display init ────────────────────────────────────────────────────
+
+pub async fn create_display(parts: DisplayParts) -> Option<DisplayDriver> {
+    let DisplayParts {
+        interface,
+        rst_pin,
+        mut vdd_en,
+        mut backlight,
+    } = parts;
+
+    // 1. Drive TFT VDD enable LOW (active LOW per Meshtastic) and let
+    //    the rail settle. Heltec's schematic has the panel power gated
+    //    by P0.03 — touching SPI before VDD is stable produces snow.
+    vdd_en.set_low();
+    Timer::after_millis(50).await;
+
+    // 2. Build the lcd-async display.
+    //    The T114 panel is wired natively portrait (135w × 240h) at
+    //    chip framebuffer offset (52, 40) — the standard 1.14" 135×240
+    //    ST7789 die mapping. Deg90 rotation rotates the user-facing
+    //    surface to landscape (240w × 135h). Meshtastic's variant.h
+    //    sets TFT_OFFSET_X=0/Y=0 because their fork of TFT_eSPI applies
+    //    these offsets internally; lcd-async expects them in display_offset.
+    //    If the image comes up mirrored or upside-down, swap
+    //    Deg90 ↔ Deg270 or set `mirrored = true`.
+    let mut delay = Delay;
+    let panel = match lcd_async::Builder::new(ST7789, interface)
+        .reset_pin(rst_pin)
+        .display_size(135, 240)
+        .display_offset(52, 40)
+        .orientation(Orientation::new().rotate(Rotation::Deg90))
+        .invert_colors(ColorInversion::Inverted)
+        .init(&mut delay)
+        .await
+    {
+        Ok(p) => p,
+        Err(_) => {
+            defmt::error!("ST7789 init failed");
+            return None;
+        }
+    };
+    defmt::info!("ST7789 init OK");
+
+    // 3. Bring the backlight up at full brightness. Stage 2 uses the
+    //    full-on duty; the splash dimming logic handled by the display
+    //    statechart will hand off to set_dim/set_bright shortly.
+    backlight.set_duty(0, embassy_nrf::pwm::DutyCycle::inverted(0));
+
+    // Forget vdd_en so it stays driven for the lifetime of the program.
+    // We took it by move so we could call set_low() during init.
+    core::mem::forget(vdd_en);
+
+    // Take the static framebuffer (240×135 × 2 bytes Rgb565 BE
+    // = 64,800 bytes zero-initialized in .bss). Stored as raw bytes
+    // so present() can DMA-blit the slice straight to the panel
+    // without an iterator-conversion pass — the lcd-async
+    // `RawFrameBuf<Rgb565, _>` wrapper handles BE byte packing on
+    // each pixel write.
+    static FRAMEBUFFER: ConstStaticCell<[u8; FB_BYTES]> =
+        ConstStaticCell::new([0u8; FB_BYTES]);
+    let fb = FRAMEBUFFER.take();
+
+    Some(St7789Color::new(panel, backlight, fb))
+}
+
+// ── Board init ──────────────────────────────────────────────────────
+
+pub struct Board {
+    p: embassy_nrf::Peripherals,
+}
+
+impl LoRaBoard for Board {
+    const NAME: &'static str = "Heltec Mesh Node T114";
+    const TX_POWER_RANGE: (i8, i8) = (-9, 22);
+
+    type RadioParts = RadioParts;
+    type CommParts = UsbParts;
+    type DisplayParts = DisplayParts;
+    type DisplayDriver = DisplayDriver;
+    type LedDriver = LedDriver;
+
+    fn init() -> Self {
+        // USB requires the 32 MHz HFXO (±50 ppm); the RC oscillator is out of spec.
+        let mut config = embassy_nrf::config::Config::default();
+        config.hfclk_source = embassy_nrf::config::HfclkSource::ExternalXtal;
+        config.lfclk_source = embassy_nrf::config::LfclkSource::ExternalXtal;
+        let p = embassy_nrf::init(config);
+        Self { p }
+    }
+
+    fn mac_address() -> [u8; 6] {
+        mcu::mac_address()
+    }
+
+    fn into_parts(self) -> BoardParts<RadioParts, UsbParts, DisplayParts, LedDriver> {
+        let p = self.p;
+
+        // ── VEXT_ENABLE (P0.21, active HIGH) ────────────────────
+        // Powers the SX1262 *and* the TFT/peripheral 3V3 rail. Must be
+        // driven HIGH before any SPI traffic to the radio or panel —
+        // without this, lora-phy init can succeed (SPI bus works
+        // electrically) but TX_DONE never fires because the PA is
+        // unpowered. Held forever via core::mem::forget. Mirrors
+        // Meshtastic's `VEXT_ENABLE = P0.21, VEXT_ON_VALUE = HIGH`.
+        let vext_en = Output::new(p.P0_21, Level::High, OutputDrive::Standard);
+        core::mem::forget(vext_en);
+
+        // ── SPI3 bus for SX1262 ─────────────────────────────────
+        // Per Heltec T114 schematic + Meshtastic variant.h:
+        //   SCK=P0.19, MOSI=P0.22, MISO=P0.23
+        //   NSS=P0.24, RST=P0.25, BUSY=P0.17, DIO1=P0.20
+        // No external RXEN/TXEN — antenna switch is driven internally
+        // by SX1262 DIO2. TCXO is on DIO3 at 1.8 V.
+        let mut spi_cfg = spim::Config::default();
+        spi_cfg.frequency = spim::Frequency::M1;
+        let spi = Spim::new(p.SPI3, mcu::Irqs, p.P0_19, p.P0_23, p.P0_22, spi_cfg);
+        let spi_bus = mcu::share_spi_bus(spi);
+
+        let nss = Output::new(p.P0_24, Level::High, OutputDrive::Standard);
+        let spi_device = SpiDevice::new(spi_bus, nss);
+
+        let reset = Output::new(p.P0_25, Level::High, OutputDrive::Standard);
+        let dio1 = Input::new(p.P0_20, Pull::Down);
+        // BUSY has an internal 20 kΩ pull-up on the SX1262 die (datasheet
+        // p. 53); an MCU-side Pull fights it. See lora-rs/lora-rs#260.
+        let busy = Input::new(p.P0_17, Pull::None);
+
+        let iv = GenericSx126xInterfaceVariant::new(reset, dio1, busy, None, None)
+            .expect("SX1262 interface init");
+
+        let sx_config = sx126x::Config {
+            chip: Sx1262,
+            tcxo_ctrl: Some(sx126x::TcxoCtrlVoltage::Ctrl1V8),
+            use_dcdc: true,
+            rx_boost: false,
+        };
+
+        let radio = RadioParts {
+            driver: Sx126x::new(spi_device, iv, sx_config),
+            delay: Delay,
+        };
+
+        // ── USB ─────────────────────────────────────────────────
+        let vbus = mcu::alloc_vbus_detect(true, true);
+        let host = UsbParts {
+            driver: Driver::new(p.USBD, mcu::Irqs, vbus),
+        };
+
+        // Battery divider control (P0.06) LOW disables the divider —
+        // saves a few tens of µA. Battery sense (P0.04 / AIN2) deferred
+        // until the protocol gets a battery field.
+        let bat_ctl = Output::new(p.P0_06, Level::Low, OutputDrive::Standard);
+        core::mem::forget(bat_ctl);
+
+        // ── SPI2 bus for ST7789 TFT ─────────────────────────────
+        // Per Meshtastic variant.h:
+        //   SCK=P1.08, MOSI=P1.09, CS=P0.11, DC=P0.12, RST=P0.02
+        //   VDD enable=P0.03 (active HIGH), Backlight=P0.15 (active LOW PWM)
+        // Write-only bus — embassy_nrf::Spim still requires a MISO slot,
+        // so we wire a free unused pin (P1.06) as a no-op input.
+        let mut tft_spi_cfg = spim::Config::default();
+        // 8 MHz lets us repaint the 240×135 panel comfortably. Higher
+        // rates work with mipidsi but are platform-dependent (board
+        // routing, pull strengths). 8 MHz is the safe default.
+        tft_spi_cfg.frequency = spim::Frequency::M8;
+        let tft_spi = Spim::new(p.SPI2, mcu::Irqs, p.P1_08, p.P1_06, p.P1_09, tft_spi_cfg);
+
+        let tft_cs = Output::new(p.P0_11, Level::High, OutputDrive::Standard);
+        let tft_dc = Output::new(p.P0_12, Level::Low, OutputDrive::Standard);
+        let tft_rst = Output::new(p.P0_02, Level::High, OutputDrive::Standard);
+        // VTFT_CTRL is active LOW per Meshtastic
+        // (`#define TFT_BACKLIGHT_ON LOW`, `digitalWrite(VTFT_CTRL, LOW)`
+        // at boot). Start HIGH (panel rail off); create_display drives
+        // LOW to enable the panel.
+        let tft_vdd = Output::new(p.P0_03, Level::High, OutputDrive::Standard);
+
+        let tft_spi_device = ExclusiveDevice::new(tft_spi, tft_cs, Delay)
+            .expect("TFT ExclusiveDevice init");
+
+        // lcd-async's SpiInterface streams pixel data directly from
+        // the caller's slice — no scratch buffer required (mipidsi's
+        // sync version needed one for batching).
+        let tft_interface = SpiInterface::new(tft_spi_device, tft_dc);
+
+        // ── PWM backlight (active-LOW on P0.15) ─────────────────
+        // Default SimpleConfig is fine — countertop=1000 → ~1 kHz
+        // (well above flicker threshold), prescaler default. Channel 0
+        // idle level matches the active-LOW wiring.
+        let mut bl_cfg = SimpleConfig::default();
+        bl_cfg.max_duty = crate::driver::st7789::BL_MAX;
+        bl_cfg.prescaler = Prescaler::Div128;
+        bl_cfg.ch0_idle_level = Level::High;
+        let backlight = SimplePwm::new_1ch(p.PWM0, p.P0_15, &bl_cfg);
+
+        let display_parts = DisplayParts {
+            interface: tft_interface,
+            rst_pin: tft_rst,
+            vdd_en: tft_vdd,
+            backlight,
+        };
+
+        // ── Green LED (P1.03, active LOW) ───────────────────────
+        // Idle level HIGH = LED off. InvertedPin flips polarity so
+        // SimpleLed can use normal "set_high = on" semantics.
+        let led_pin = Output::new(p.P1_03, Level::High, OutputDrive::Standard);
+        let led = SimpleLed(InvertedPin(led_pin));
+
+        BoardParts {
+            radio,
+            host,
+            display: Some(display_parts),
+            led,
+            mac: Self::mac_address(),
+        }
+    }
+}

src/board/lilygo_tbeam_supreme.rs

@@ -50,8 +50,8 @@ pub struct DisplayParts {
 
 // ── Display init ────────────────────────────────────────────────────
 
-pub async fn create_display(i2c: DisplayI2c) -> Option<DisplayDriver> {
-    let mut display = Sh1106::new(i2c, 0x3C);
+pub async fn create_display(parts: DisplayParts) -> Option<DisplayDriver> {
+    let mut display = Sh1106::new(parts.i2c, 0x3C);
 
     embassy_time::Timer::after_millis(100).await;
     if display.init().await.is_err() {

src/board/rak_wisblock_4631.rs

@@ -52,8 +52,8 @@ pub struct DisplayParts {
 
 // ── Display init ────────────────────────────────────────────────────
 
-pub async fn create_display(i2c: DisplayI2c) -> Option<DisplayDriver> {
-    let mut display = crate::driver::sh1106::Sh1106::new(i2c, 0x3C);
+pub async fn create_display(parts: DisplayParts) -> Option<DisplayDriver> {
+    let mut display = crate::driver::sh1106::Sh1106::new(parts.i2c, 0x3C);
 
     // Retry 3× with 100ms backoff. The SH1106's first transaction
     // after power-on can return Err if the chip's internal voltage

src/board/traits.rs

@@ -6,10 +6,7 @@
 //!
 //! 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;
-
-use crate::driver::DisplayBrightness;
+use crate::display::BoardDisplay;
 
 /// Async RGB LED control. Boards without an LED use `()` which is a no-op.
 pub trait RgbLed {
@@ -37,9 +34,10 @@ pub trait LoRaBoard: Sized {
     /// Display peripheral bundle (I2C bus for display init).
     type DisplayParts;
 
-    /// Concrete display driver type (must implement DrawTarget for rendering
-    /// and DisplayBrightness for the two-level dim control).
-    type DisplayDriver: DrawTarget<Color = BinaryColor> + DisplayBrightness;
+    /// Concrete display driver type. Each board's driver implements
+    /// [`BoardDisplay`] to render the splash + dashboard content into its
+    /// native pixel format and resolution and to flush / dim the panel.
+    type DisplayDriver: BoardDisplay;
 
     /// RGB LED driver. Boards without an LED use `()`.
     type LedDriver: RgbLed;

src/board/waveshare_rp2040_lora.rs

@@ -41,12 +41,16 @@ pub struct UsbParts {
 }
 
 pub struct DisplayParts {
+    // No display on this board, but the trait still wants concrete
+    // peripheral types. The i2c bus type is reserved for the future
+    // possibility of an external OLED add-on.
+    #[allow(dead_code)]
     pub i2c: DisplayI2c,
 }
 
 // ── Display init ───────────────────────────────────────────────────
 
-pub async fn create_display(_i2c: DisplayI2c) -> Option<DisplayDriver> {
+pub async fn create_display(_parts: DisplayParts) -> Option<DisplayDriver> {
     None
 }
 

src/board/wio_tracker_l1.rs

@@ -42,8 +42,8 @@ pub struct DisplayParts {
 
 // ── Display init ────────────────────────────────────────────────────
 
-pub async fn create_display(i2c: DisplayI2c) -> Option<DisplayDriver> {
-    let mut display = crate::driver::sh1106::Sh1106::new(i2c, 0x3D);
+pub async fn create_display(parts: DisplayParts) -> Option<DisplayDriver> {
+    let mut display = crate::driver::sh1106::Sh1106::new(parts.i2c, 0x3D);
 
     embassy_time::Timer::after_millis(100).await;
     if display.init().await.is_err() {