refactor: build system auto-discovery, updated docs

- build.rs discovers boards by content (implements LoRaBoard), not exclusion lists
- build.rs auto-discovers helper modules by scanning board files for use super::<helper>
- Jinja template dynamically generates cfg gates for helpers
- Updated PORTING.md for new architecture (hal/, driver/, BoardParts, associated types)
- Zero manual template editing needed when adding boards to existing MCU families

build.rs

@@ -1,32 +1,48 @@
 use minijinja::{context, Environment};
 use owo_colors::OwoColorize;
+use std::collections::HashMap;
 use std::fs;
 
 fn main() {
-    // Protocol tests run on the host without a board feature. Cargo doesn't
-    // expose `cfg(test)` to build scripts, so we rely on an env var set by
-    // the justfile `test` recipe. See: `just test`
+    // Protocol tests run on the host without a board feature.
     if std::env::var_os("DONGLORA_HOST_TEST").is_some() {
         return;
     }
 
     let board_dir = "src/board";
-    let boards: Vec<String> = fs::read_dir(board_dir)
-        .expect("failed to read src/board directory")
-        .filter_map(|e| {
-            let p = e.ok()?.path();
-            let stem = p.file_stem()?.to_str()?;
-            // Exclude non-board files: mod.rs, traits.rs, and platform helpers (esp32s3.rs).
-            if p.is_file()
-                && p.extension()? == "rs"
-                && !matches!(stem, "mod" | "traits" | "esp32s3")
-            {
-                return Some(p.file_stem()?.to_str()?.to_string());
-            }
-            None
-        })
-        .collect();
 
+    // ── Discover boards vs helpers by content ───────────────────────
+    //
+    // A .rs file in src/board/ that implements LoRaBoard is a board.
+    // Everything else (traits.rs, esp32s3.rs, etc.) is a helper module.
+    // No exclusion lists — detection is based on what the file contains.
+    let mut boards: Vec<String> = Vec::new();
+
+    for entry in fs::read_dir(board_dir).expect("failed to read src/board directory") {
+        let p = match entry {
+            Ok(e) => e.path(),
+            Err(_) => continue,
+        };
+        if !p.is_file() || p.extension().and_then(|e| e.to_str()) != Some("rs") {
+            continue;
+        }
+        let stem = match p.file_stem().and_then(|s| s.to_str()) {
+            Some("mod") => continue, // Skip generated file
+            Some(s) => s.to_string(),
+            None => continue,
+        };
+        let content = match fs::read_to_string(&p) {
+            Ok(c) => c,
+            Err(_) => continue,
+        };
+        if content.contains("LoRaBoard for Board") {
+            boards.push(stem);
+        }
+    }
+
+    boards.sort(); // Deterministic ordering
+
+    // ── Validate exactly one board feature is enabled ───────────────
     let enabled: Vec<_> = std::env::vars()
         .filter(|(k, _)| k.starts_with("CARGO_FEATURE_"))
         .map(|(k, _)| k.replace("CARGO_FEATURE_", "").to_lowercase())
@@ -49,6 +65,35 @@ fn main() {
         ),
     }
 
+    // ── Auto-discover helper modules used by board files ────────────
+    //
+    // Scan each board file for `use super::<name>` to find which helper
+    // modules they depend on. Generate cfg gates so helpers compile only
+    // when a dependent board is selected.
+    let mut helper_boards: HashMap<String, Vec<String>> = HashMap::new();
+
+    for board in &boards {
+        let path = format!("{}/{}.rs", board_dir, board);
+        if let Ok(content) = fs::read_to_string(&path) {
+            for line in content.lines() {
+                let trimmed = line.trim();
+                if let Some(rest) = trimmed.strip_prefix("use super::") {
+                    let helper = rest
+                        .split(|c: char| !c.is_alphanumeric() && c != '_')
+                        .next()
+                        .unwrap_or("");
+                    if !helper.is_empty() && helper != "traits" {
+                        helper_boards
+                            .entry(helper.to_string())
+                            .or_default()
+                            .push(board.clone());
+                    }
+                }
+            }
+        }
+    }
+
+    // ── Render board module template ────────────────────────────────
     let mut env = Environment::new();
     let template = fs::read_to_string("src/board/mod.rs.j2").expect("missing src/board/mod.rs.j2");
     env.add_template("mod", &template)
@@ -56,7 +101,7 @@ fn main() {
     let rendered = env
         .get_template("mod")
         .expect("template not found")
-        .render(context!(boards => boards))
+        .render(context!(boards => boards, helpers => helper_boards))
         .expect("failed to render board module");
     fs::write("src/board/mod.rs", rendered).expect("failed to write src/board/mod.rs");
 
@@ -64,9 +109,7 @@ fn main() {
     println!("cargo:rerun-if-changed={}", board_dir);
 
     // cortex-m-rt's link.x does `INCLUDE memory.x`. Copy our nRF layout into
-    // OUT_DIR (which cortex-m-rt already adds to the linker search path) so it's
-    // only visible to ARM builds. Keeping it out of the project root prevents
-    // the linker from shadowing esp-hal's generated memory.x on Xtensa builds.
+    // OUT_DIR so it's only visible to ARM builds.
     let target = std::env::var("TARGET").unwrap_or_default();
     if !target.starts_with("xtensa") {
         let out_dir = std::env::var("OUT_DIR").unwrap();

src/board/PORTING.md

@@ -5,14 +5,14 @@
 ### 1. Create the board file
 
 Create `src/board/your_board.rs`. Use an existing board as a template:
-- ESP32-S3 boards: copy `heltec_v4.rs` (uses shared helpers from `esp32s3.rs`)
-- nRF52840 boards: copy `rak_wisblock_4631.rs`
+- ESP32-S3 boards: copy `heltec_v4.rs` (uses shared helpers from `board/esp32s3.rs` and `hal/esp32s3.rs`)
+- nRF52840 boards: copy `rak_wisblock_4631.rs` (uses shared helpers from `hal/nrf52840.rs`)
+- New MCU family: create a new `hal/<mcu>.rs` with MCU primitives first
 
-ESP32-S3 boards share common type aliases, peripheral bundles, and init helpers
-via `src/board/esp32s3.rs`. Your board file only needs the trait impl and
-board-specific init (Vext GPIO, display reset). If you add a new ESP32-S3 board,
-add its feature to the `#[cfg(any(...))]` gate on `mod esp32s3` in
-`src/board/mod.rs.j2`.
+`build.rs` auto-discovers your board file — any `.rs` file in `src/board/` that
+implements `LoRaBoard for Board` is automatically detected as a board. Helper
+modules (like `esp32s3.rs`) are auto-discovered via `use super::<helper>` imports
+in board files. No template editing or exclusion lists needed.
 
 ### 2. Define concrete types
 
@@ -21,7 +21,9 @@ Your board must export these type aliases:
 ```rust
 pub type RadioDriver = ...; // Must work with lora_phy::LoRa<RadioDriver, Delay>
 pub type UsbDriver = ...;   // Must implement embassy_usb_driver::Driver<'static>
+                             // (or UartDriver for UART boards)
 pub type DisplayI2c = ...;  // Must implement embedded_hal_async::i2c::I2c
+pub type DisplayDriver = ...; // Must implement DrawTarget<Color = BinaryColor>
 ```
 
 ### 3. Define peripheral bundles
@@ -32,39 +34,43 @@ pub struct RadioParts {
     pub delay: embassy_time::Delay,
 }
 
-pub struct UsbParts {
+pub struct UsbParts {  // or UartParts for UART boards
     pub driver: UsbDriver,
 }
 
 pub struct DisplayParts {
     pub i2c: DisplayI2c,
-    pub mac: [u8; 6],
 }
 ```
 
 ### 4. Implement the LoRaBoard trait
 
 ```rust
-use super::traits::LoRaBoard;
+use super::traits::{BoardParts, LoRaBoard};
 
 impl LoRaBoard for Board {
     const NAME: &'static str = "Your Board Name";
     const TX_POWER_RANGE: (i8, i8) = (-9, 22); // check your radio + PA
+
+    type RadioParts = RadioParts;
+    type CommParts = UsbParts;       // or UartParts
+    type DisplayParts = DisplayParts;
+    type DisplayDriver = DisplayDriver;
+
     fn init() -> Self { ... }
     fn mac_address() -> [u8; 6] { ... } // read from efuse, FICR, etc.
+    fn into_parts(self) -> BoardParts<RadioParts, UsbParts, DisplayParts> {
+        // Initialize buses via hal::, construct drivers, return BoardParts
+        BoardParts { radio, host, display: Some(display_parts), mac: Self::mac_address() }
+    }
 }
 ```
 
-The compiler will refuse to build if any of these are missing.
-
-### 5. Implement `Board::into_parts()`
+### 5. Add display init
 
 ```rust
-impl Board {
-    pub fn into_parts(self) -> (RadioParts, UsbParts, Option<DisplayParts>) {
-        // Initialize SPI, DMA, radio, USB, I2C
-        // Return peripheral bundles
-    }
+pub async fn create_display(i2c: DisplayI2c) -> Option<DisplayDriver> {
+    // Construct and initialize your display driver (SSD1306, SH1106, etc.)
 }
 ```
 
@@ -79,7 +85,7 @@ your_board = ["dep:your-hal", ...]
 
 ### 7. Add to justfile
 
-Add your board's feature/target/chip to the `boards` list at the top of `justfile`.
+Add your board's feature/target/chip to the board definitions at the top of `justfile`.
 
 ### 8. Build and test
 
@@ -88,5 +94,3 @@ just check your_board    # Must compile
 just clippy your_board   # Must be clean
 just build your_board    # Produces firmware
 ```
-
-`build.rs` auto-discovers your `.rs` file — no template editing needed.

src/board/mod.rs.j2

@@ -2,9 +2,10 @@
 pub mod traits;
 pub use traits::*;
 
-#[cfg(any(feature = "heltec_v3", feature = "heltec_v4"))]
-mod esp32s3;
-
+{% for helper, helper_features in helpers|items -%}
+#[cfg(any({% for f in helper_features %}feature = "{{ f }}"{% if not loop.last %}, {% endif %}{% endfor %}))]
+mod {{ helper }};
+{% endfor %}
 cfg_if::cfg_if! {
     {%- for board in boards %}
     {% if loop.first %}if{% else %}else if{% endif %} #[cfg(feature = "{{ board }}")] {