feat(boards): LilyGo T-Beam (classic) support

First classic-ESP32 (non-S3) board in the firmware, and first SX127x
radio. ESP32 + SX1276 + SSD1306 OLED + AXP192 PMIC, CP2102 USB-UART
bridge. Pin map verified from MeshCore variants/lilygo_tbeam_SX1276.

The AXP192 gates power to the LoRa chip and OLED. Its I²C bus is
shared with the display, so the firmware builds I²C0 in blocking mode
first for the PMIC init, then converts the same handle to async and
hands it to the display task — avoids double-consuming the peripheral.

Lora-phy's Sx127x support drives DIO0 as the sole IRQ (SX127x has no
BUSY line); the chip runs from a crystal, tx_boost routes +20 dBm
through PA_BOOST.

The `esp-hal` / `esp-rtos` / `esp-backtrace` / `esp-println` deps have
been restructured so the chip flavour (esp32 vs esp32s3) is selected
at the per-board feature level instead of baked into the dep lines.
This keeps the existing S3 boards building on esp32s3 while the new
T-Beam feature selects classic esp32 via the same dependency set.

LoRaBoard gains supported_sf_bitmap() / supported_bw_bitmap() methods
(with SX126x defaults) so the T-Beam can report SF6–SF12 via GET_INFO
— the SX1276 has no SF5. radio_chip_id() reports 0x0011 per
donglora-protocol RadioChipId::Sx1276. freq_range_hz widens to the
SX1276 datasheet span of 137 MHz–1020 MHz.

New modules:
- src/hal/esp32.rs           — classic-ESP32 MCU primitives
- src/board/esp32.rs         — Sx127x radio + SSD1306 display pipe
- src/board/lilygo_tbeam.rs  — the board file
- src/driver/axp.rs          — AXP192 init added alongside AXP2101

src/board/esp32.rs

@@ -0,0 +1,103 @@
+//! Shared types and peripheral wiring for classic-ESP32 SX1276 boards.
+//!
+//! Counterpart to `board::esp32s3` for the SX126x line. Builds an
+//! `Sx127x<Sx1276>` driver from an already-initialized SPI bus plus the
+//! board's reset and DIO0 pins. SX127x has no `BUSY` line — DIO0 carries
+//! every IRQ (TX done, RX done, header valid, …) and lora-phy's
+//! `GenericSx127xInterfaceVariant` waits on it directly.
+
+use embassy_embedded_hal::shared_bus::asynch::spi::SpiDevice;
+use embassy_sync::blocking_mutex::raw::NoopRawMutex;
+use embassy_time::Delay;
+use esp_hal::gpio::{Input, InputConfig, InputPin, Level, Output, OutputConfig, OutputPin, Pull};
+
+use lora_phy::iv::GenericSx127xInterfaceVariant;
+use lora_phy::sx127x::{self, Sx127x};
+
+use crate::hal::esp32 as mcu;
+
+// ── Re-export MCU types ─────────────────────────────────────────────
+
+pub use mcu::{I2cBus as DisplayI2c, SpiBus};
+
+// ── Concrete peripheral types ───────────────────────────────────────
+
+type Nss = Output<'static>;
+type Iv = GenericSx127xInterfaceVariant<Output<'static>, Input<'static>>;
+type RadioSpiDevice = SpiDevice<'static, NoopRawMutex, SpiBus, Nss>;
+pub type RadioDriver = Sx127x<RadioSpiDevice, Iv, sx127x::Sx1276>;
+
+// ── Peripheral bundles ──────────────────────────────────────────────
+
+pub struct RadioParts {
+    pub driver: RadioDriver,
+    pub delay: Delay,
+}
+
+pub struct DisplayParts {
+    pub i2c: DisplayI2c,
+}
+
+// ── Display driver ──────────────────────────────────────────────────
+
+pub type DisplayDriver = ssd1306::Ssd1306Async<
+    ssd1306::prelude::I2CInterface<DisplayI2c>,
+    ssd1306::size::DisplaySize128x64,
+    ssd1306::mode::BufferedGraphicsModeAsync<ssd1306::size::DisplaySize128x64>,
+>;
+
+/// Construct and initialize an SSD1306 display from raw I²C.
+pub async fn create_display(i2c: DisplayI2c) -> 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 mut display = Ssd1306Async::new(interface, DisplaySize128x64, DisplayRotation::Rotate0)
+        .into_buffered_graphics_mode();
+
+    embassy_time::Timer::after_millis(100).await;
+    if display.init().await.is_err() {
+        defmt::error!("SSD1306 display init failed");
+        return None;
+    }
+    let _ = display.set_brightness(Brightness::BRIGHTEST).await;
+    Some(display)
+}
+
+// ── Shared peripheral init helpers ──────────────────────────────────
+
+/// Construct an SX1276 radio from an initialized SPI bus.
+///
+/// `dio0` is the primary IRQ (TX/RX done). The SX1276 module on the T-Beam
+/// runs from a crystal oscillator, not a TCXO, and power comes from the
+/// AXP192's PA_BOOST rail — `tx_boost = true` routes TX through the PA
+/// output for +20 dBm.
+pub fn init_radio(
+    spi_bus: &'static embassy_sync::mutex::Mutex<NoopRawMutex, SpiBus>,
+    nss_pin: impl OutputPin + 'static,
+    reset_pin: impl OutputPin + 'static,
+    dio0_pin: impl InputPin + 'static,
+) -> RadioParts {
+    let nss = Output::new(nss_pin, Level::High, OutputConfig::default());
+    let spi_device = SpiDevice::new(spi_bus, nss);
+
+    let reset = Output::new(reset_pin, Level::High, OutputConfig::default());
+    let dio0 = Input::new(dio0_pin, InputConfig::default().with_pull(Pull::Down));
+
+    let iv = GenericSx127xInterfaceVariant::new(reset, dio0, None, None)
+        .expect("SX1276 interface init");
+
+    let sx_config = sx127x::Config {
+        chip: sx127x::Sx1276,
+        tcxo_used: false,
+        tx_boost: true,
+        rx_boost: false,
+    };
+
+    RadioParts {
+        driver: Sx127x::new(spi_device, iv, sx_config),
+        delay: Delay,
+    }
+}

src/board/lilygo_tbeam.rs

@@ -0,0 +1,137 @@
+//! LilyGo T-Beam (classic) — ESP32 + SX1276 + SSD1306 OLED + AXP192 PMIC.
+//!
+//! First-generation T-Beam. ESP32 (dual-core Xtensa LX6, no native USB),
+//! SX1276 module with XTAL (no TCXO), 128×64 SSD1306 OLED, AXP192 PMIC
+//! gating the LoRa and OLED rails, CP2102 USB-UART bridge for host I/O.
+//!
+//! The AXP192 shares an I²C bus with the OLED (SDA=21, SCL=22). PMIC init
+//! runs blocking on that bus first, then the same pins are re-initialized
+//! in async mode for the display task.
+//!
+//! Pin map (verified from MeshCore variants/lilygo_tbeam_SX1276/):
+//!   LoRa SPI:  SCK=5, MOSI=27, MISO=19, CS=18
+//!   LoRa ctl:  RESET=23, DIO0=26 (primary IRQ — SX127x has no BUSY)
+//!   OLED I²C:  SDA=21, SCL=22, SSD1306 @ 0x3C (shared with AXP192 @ 0x34)
+//!   UART host: TX=1, RX=3 via CP2102 bridge (USB 10c4:ea60)
+//!   LED:       GPIO4 (active HIGH — reuses MeshCore's P_LORA_TX_LED)
+//!
+//! GPS / battery / IMU / PCF8563 RTC are populated on the board but unused
+//! by this firmware.
+
+use esp_hal::gpio::{Level, Output, OutputConfig};
+use esp_hal::i2c::master::{Config as I2cConfig, I2c};
+
+use super::esp32;
+use super::traits::{BoardParts, LoRaBoard};
+use crate::driver::axp;
+use crate::driver::simple_led::SimpleLed;
+use crate::hal::esp32 as mcu;
+use crate::protocol::RadioChipId;
+
+pub use super::esp32::{create_display, DisplayDriver, DisplayParts, RadioDriver, RadioParts};
+
+// ── Concrete peripheral types ───────────────────────────────────────
+
+pub type UartDriver = esp_hal::uart::Uart<'static, esp_hal::Async>;
+pub type LedDriver = SimpleLed<Output<'static>>;
+
+// ── Peripheral bundles ──────────────────────────────────────────────
+
+pub struct UartParts {
+    pub driver: UartDriver,
+}
+
+// ── Board init ──────────────────────────────────────────────────────
+
+pub struct Board {
+    p: esp_hal::peripherals::Peripherals,
+}
+
+impl LoRaBoard for Board {
+    const NAME: &'static str = "LilyGo T-Beam";
+    // SX1276 PA_BOOST range per the datasheet: +2 dBm min, +20 dBm max.
+    const TX_POWER_RANGE: (i8, i8) = (2, 20);
+
+    type RadioParts = RadioParts;
+    type CommParts = UartParts;
+    type DisplayParts = DisplayParts;
+    type DisplayDriver = DisplayDriver;
+    type LedDriver = LedDriver;
+
+    fn init() -> Self {
+        let p = esp_hal::init(esp_hal::Config::default());
+        Self { p }
+    }
+
+    fn mac_address() -> [u8; 6] {
+        mcu::mac_address()
+    }
+
+    fn radio_chip_id() -> u16 {
+        RadioChipId::Sx1276.as_u16()
+    }
+
+    fn freq_range_hz() -> (u32, u32) {
+        // SX1276 tuning window per datasheet (LF + HF bands combined).
+        (137_000_000, 1_020_000_000)
+    }
+
+    fn supported_sf_bitmap() -> u16 {
+        // SX127x supports SF6–SF12 (no SF5 like the SX126x).
+        0x1FC0
+    }
+
+    fn into_parts(self) -> BoardParts<RadioParts, UartParts, DisplayParts, LedDriver> {
+        let p = self.p;
+
+        mcu::start_timer(p.TIMG0, p.SW_INTERRUPT);
+
+        // AXP192 and SSD1306 share I²C0 (SDA=21, SCL=22). Build the bus
+        // once as blocking, drive the PMIC init, then convert to async for
+        // the display task — avoids re-consuming the I²C0 peripheral.
+        // PMIC failure isn't fatal to boot: log and proceed so the rest of
+        // the firmware can still emit diagnostics.
+        let mut i2c_blocking = I2c::new(p.I2C0, I2cConfig::default())
+            .expect("I2C0 init")
+            .with_sda(p.GPIO21)
+            .with_scl(p.GPIO22);
+        if let Err(_e) = axp::axp192_init_lora_oled(&mut i2c_blocking) {
+            defmt::error!("AXP192 init failed — LoRa rail may be dead");
+        }
+        // Let DCDC1 / LDO2 settle before SPI or display traffic.
+        esp_hal::delay::Delay::new().delay_millis(20);
+
+        // SPI2 for SX1276: SCK=5, MOSI=27, MISO=19
+        let spi_bus = mcu::init_spi(p.SPI2, p.DMA_SPI2, p.GPIO5, p.GPIO27, p.GPIO19);
+
+        // SX1276: CS=18, RESET=23, DIO0=26 (primary IRQ)
+        let radio = esp32::init_radio(spi_bus, p.GPIO18, p.GPIO23, p.GPIO26);
+
+        // UART0 via CP2102 bridge: TX=1, RX=3 (ESP32 default console)
+        use esp_hal::uart::{Config as UartConfig, Uart};
+        let host = UartParts {
+            driver: Uart::new(p.UART0, UartConfig::default())
+                .expect("UART init")
+                .with_tx(p.GPIO1)
+                .with_rx(p.GPIO3)
+                .into_async(),
+        };
+
+        // Hand the (now async) I²C bus to the SSD1306 display task.
+        let display = Some(DisplayParts {
+            i2c: i2c_blocking.into_async(),
+        });
+
+        // TX activity LED on GPIO4 (active HIGH).
+        let led_pin = Output::new(p.GPIO4, Level::Low, OutputConfig::default());
+        let led = SimpleLed(led_pin);
+
+        BoardParts {
+            radio,
+            host,
+            display,
+            led,
+            mac: Self::mac_address(),
+        }
+    }
+}

src/board/mod.rs.j2

@@ -3,7 +3,11 @@ pub mod traits;
 pub use traits::*;
 
 {% for helper, helper_features in helpers|items -%}
+{% if helper_features|length == 1 -%}
+#[cfg(feature = "{{ helper_features[0] }}")]
+{% else -%}
 #[cfg(any({% for f in helper_features %}feature = "{{ f }}"{% if not loop.last %}, {% endif %}{% endfor %}))]
+{% endif -%}
 mod {{ helper }};
 {% endfor %}
 cfg_if::cfg_if! {

src/board/traits.rs

@@ -65,6 +65,21 @@ pub trait LoRaBoard: Sized {
         (150_000_000, 960_000_000)
     }
 
+    /// Bitmap of supported LoRa spreading factors — bit N = SF N. Defaults
+    /// to SX126x's SF5–SF12 (`0x1FE0`). SX127x boards must override to
+    /// `0x1FC0` (SF6–SF12); LLCC68 boards to `0x0FE0` (SF5–SF11).
+    fn supported_sf_bitmap() -> u16 {
+        0x1FE0
+    }
+
+    /// Bitmap of supported LoRa bandwidths. Bit positions match
+    /// `LoRaBandwidth::as_u8()` (sub-GHz BW enum values 0..9). Defaults
+    /// to all sub-GHz BWs (`0x03FF`). SX128x boards flip the 2.4 GHz
+    /// bits when we add them.
+    fn supported_bw_bitmap() -> u16 {
+        0x03FF
+    }
+
     /// Decompose initialized board into peripheral bundles for each task.
     fn into_parts(
         self,