initial commit

.cargo/config.toml

@@ -0,0 +1,17 @@
+[target.riscv32imac-unknown-none-elf]
+runner = "espflash flash --monitor --chip esp32c5"
+
+[env]
+ESP_LOG="info"
+
+[build]
+rustflags = [
+  # Required to obtain backtraces (e.g. when using the "esp-backtrace" crate.)
+  # NOTE: May negatively impact performance of produced code
+  "-C", "force-frame-pointers",
+]
+
+target = "riscv32imac-unknown-none-elf"
+
+[unstable]
+build-std = ["alloc", "core"]

.clippy.toml

@@ -0,0 +1,2 @@
+stack-size-threshold = 1024
+doc-valid-idents = ["WiFi", "GeoNetworking", "QoS", ".."]

.gitignore

@@ -0,0 +1,29 @@
+# will have compiled files and executables
+debug/
+target/
+
+# Editor configuration
+.vscode/
+.zed/
+.helix/
+.nvim.lua
+
+# These are backup files generated by rustfmt
+**/*.rs.bk
+
+# MSVC Windows builds of rustc generate these, which store debugging information
+*.pdb
+
+# RustRover
+#  JetBrains specific template is maintained in a separate JetBrains.gitignore that can
+#  be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
+#  and can be added to the global gitignore or merged into this file.  For a more nuclear
+#  option (not recommended) you can uncomment the following to ignore the entire idea folder.
+#.idea/
+
+
+# Ignore .DS_Store file in mac
+**/.DS_Store
+
+# additional files
+/Cargo.lock

Cargo.toml

@@ -0,0 +1,39 @@
+[package]
+edition      = "2024"
+name         = "esp32-cits-core"
+rust-version = "1.88"
+version      = "0.1.0"
+
+[features]
+default = ["esp32c5"]
+
+esp32c5 = ["dep:esp-radio", "dep:esp-hal"]
+std     = ["c-its-parser/std"]
+# Enable logging output using version 0.4 of the log crate.
+log-04  = ["esp-radio/log-04", "esp-hal/log-04"]
+# Enable logging output using defmt and implement `defmt::Format` on certain types.
+defmt   = ["esp-radio/defmt", "esp-hal/defmt"]
+
+
+[dependencies]
+c-its-parser = { version = "2.4.1", default-features = false, features = [
+  "time",
+  "geo",
+  "libm",
+  "transport",
+  "extensions",
+] }
+chrono = { version = "0.4.44", default-features = false, features = ["alloc"] }
+esp-hal = { version = "~1.1.0", optional = true, features = ["esp32c5", "unstable"] }
+esp-radio = { version = "0.18.0", optional = true, features = [
+  "esp-alloc",
+  "esp32c5",
+  "unstable",
+  "wifi",
+  "sniffer",
+] }
+geo-types = { version = "0.7.19", default-features = false }
+
+[dev-dependencies]
+assert_float_eq = "1.2.0"
+env_logger = "0.11.10"

Readme.md

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+# ESP32-C5 C-ITS Core
+
+Common data structures and helper functions to receive and send C-ITS (V2X) data on an ESP32-C5.
+
+## Usage
+
+### Communicate with C-ITS Devices
+Setup the connection like this in your `main` function:
+```rust
+// Setup WiFi
+// sadly, it doesn't work any more when we move `esp_radio::wifi::new` to `setup_wifi_sniffer`
+let (mut wifi_controller, interfaces) = esp_radio::wifi::new(
+    peripherals.WIFI,
+    esp_radio::wifi::ControllerConfig::default(),
+)
+.expect("Failed to initialize Wi-Fi controller");
+
+if let Err(err) = wifi_controller.set_band_mode(esp_radio::wifi::BandMode::_5G) {
+    println!("Failed to set WiFi to 5GHz only: {err}");
+}
+if let Err(err) = wifi_controller.set_max_tx_power(WIFI_TXPOWER * 4) {
+    println!("Failed to set WiFi TX power: {err}");
+}
+
+critical_section::with(|cs| {
+    WIFI_RX_QUEUE.borrow(cs).replace(Some(ArrayQueue::new(2)));
+});
+let mut wlan_iface = interfaces.sniffer;
+radio::setup_wifi_sniffer(WIFI_CHANNEL, &mut wlan_iface, handle_frame)
+    .expect("Fatal error initializing 802.11p sniffer");
+
+println!("WiFi promiscuous mode on channel {WIFI_CHANNEL} running");
+
+let mac = esp_hal::efuse::base_mac_address();
+println!("WiFi MAC: {mac}");
+```
+
+With a frame handler like this:
+```rust
+fn handle_frame(frame: esp_radio::wifi::sniffer::PromiscuousPkt<'_>) {
+  match esp32_cits_core::rx::is_broadcast_frame(&frame) {
+    Err(err) => {
+        warn!("{err}");
+        return;
+    }
+    Ok(false) => {
+        // drop frame
+        return;
+    }
+    Ok(true) => {
+        // continue
+    }
+}
+
+  println!("Received frame with {} bytes", frame.len);
+
+  // parse message
+  match c_its_parser::de::decode(frame.data, c_its_parser::Headers::IEEE802LlcGnBtp) {
+      Ok(its_message) => {
+          println!("New message: {its_message:?}");
+
+          // do something with the data
+      },
+      Err(err) => println!("Failed to parse ITS message: {err}"),
+  }
+}
+```
+
+### Sending
+Implement `tx::GnItsPayload` and then call `encode_packet()`.
+Then send frame with `radio::send_80211_bcast_frame()`.
+
+
+### Run Unit Tests on Host
+The unit tests in this project are meant to be run on the host:
+
+```
+cargo test --target host-tuple --no-default-features -F std
+```

rustfmt.toml

@@ -0,0 +1,6 @@
+unstable_features = true
+format_code_in_doc_comments = true
+
+group_imports = "StdExternalCrate"
+imports_granularity = "Module"
+imports_layout = "HorizontalVertical"

src/lib.rs

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+//! Common ESP32 C-ITS Utilities
+
+#![cfg_attr(not(test), no_std)]
+#![cfg_attr(docsrs, feature(doc_cfg))]
+
+extern crate alloc;
+
+/// Position and Velocity Vector
+#[allow(unused)]
+#[derive(Debug, Default, Clone, PartialEq)]
+pub struct PosVel {
+    pub position: geo_types::Point,
+    pub heading_deg: Option<f32>,
+    pub speed_mps: Option<f32>,
+}
+
+pub mod radio;
+pub mod rx;
+pub mod tx;

src/radio.rs

@@ -0,0 +1,294 @@
+//! IEEE 802.11p C-ITS Capture with ESP32-C5
+#![allow(unused)]
+
+// -----------------------------
+// missing interface definitions
+// -----------------------------
+
+pub type Channel = core::ffi::c_int;
+
+unsafe extern "C" {
+    /// Changes the 802.11 PHY channel
+    ///
+    /// C function signature: `void phy_change_channel(int,int,int,int)`
+    ///
+    /// Options:
+    /// - `primary`: Channel frequency in MHz
+    /// - `ignored1`: Ignored (set to 1)
+    /// - `ignored2`: Ignored (set to 0)
+    /// - `ht_mode`: Probably HT mode
+    unsafe fn phy_change_channel(
+        primary: Channel,
+        ignored1: core::ffi::c_int,
+        ignored2: core::ffi::c_int,
+        ht_mode: core::ffi::c_int,
+    ) -> core::ffi::c_int;
+
+    /// Enables 802.11p mode on the ESP32-C5
+    ///
+    /// C function signature: `void phy_11p_set(int,int)`
+    ///
+    /// Options:
+    /// - `enable`: Boolean option to enable 802.11p mode
+    /// - `half_rate`: 5 MHz mode
+    unsafe fn phy_11p_set(enable: u8, half_rate: u8);
+
+}
+
+/// Enum values for `wifi_promiscuous_pkt_type_t` used in `esp_radio::wifi::sniffer::PromiscuousPkt::frame_type`
+///
+/// Original value is actually `core::ffi::c_uint`, but that can't be used in `#[repr()]` attributes,
+/// so we're using `u8` as the smallest suitable type here that can be casted to a bigger type.
+#[repr(u8)]
+#[derive(Debug, Clone, Copy)]
+#[allow(dead_code)]
+pub enum PromiscuousPktType {
+    /// Management frame, indicates 'buf' argument is `wifi_promiscuous_pkt_t`
+    Mgmt = 0,
+    /// Control frame, indicates 'buf' argument is `wifi_promiscuous_pkt_t`
+    Ctrl = 1,
+    /// Data frame, indicates 'buf' argument is `wifi_promiscuous_pkt_t`
+    Data = 2,
+    /// Other type, such as MIMO etc. 'buf' argument is `wifi_promiscuous_pkt_t` but the payload is zero length.
+    Misc = 3,
+}
+
+impl PromiscuousPktType {
+    #[allow(dead_code)]
+    #[must_use]
+    pub fn as_repr(self) -> u8 {
+        self as u8
+    }
+
+    /// Converts to underlying type of `wifi_promiscuous_pkt_type_t` (used by `esp_radio::wifi::sniffer::PromiscuousPkt::frame_type`)
+    #[must_use]
+    pub fn as_frame_type(self) -> core::ffi::c_uint {
+        core::ffi::c_uint::from(self.as_repr())
+    }
+
+    /// Determines if we are the same frame type as `esp_radio::wifi::sniffer::PromiscuousPkt::frame_type`
+    #[must_use]
+    pub fn matches(self, frame_type: core::ffi::c_uint) -> bool {
+        self.as_frame_type() == frame_type
+    }
+}
+
+#[cfg(feature = "esp32c5")]
+/// Configure WiFi Sniffer to a certain 802.11p channel
+///
+/// # Errors
+/// Returns a human-readable error description if setup failed
+pub fn setup_wifi_sniffer(
+    channel: Channel,
+    sniffer: &mut esp_radio::wifi::sniffer::Sniffer,
+    callback: fn(esp_radio::wifi::sniffer::PromiscuousPkt<'_>),
+) -> Result<(), alloc::string::String> {
+    sniffer
+        .set_promiscuous_mode(true)
+        .map_err(|err| alloc::format!("Failed to enable promiscuous mode: {err:?}"))?;
+
+    sniffer.set_receive_cb(callback);
+
+    // convert channel number to frequency in MHz
+    let primary = 5000 + (channel * 5);
+
+    unsafe {
+        phy_11p_set(1, 0);
+        match phy_change_channel(primary, 1, 0, 0) {
+            0 => Ok(()),
+            ret => Err(alloc::format!("Failed to change channel: {ret}")),
+        }
+    }
+}
+
+#[cfg(feature = "esp32c5")]
+/// Sends 802.11p broadcast frame
+///
+/// Expects `data` to contain GN header (BTP header and ITS payload) to be a valid C-ITS/ ITS-G5 packet/ frame.
+///
+/// # Errors
+/// Fails when MAC is not the right size or returns frame send error
+pub fn send_80211_bcast_frame(
+    sniffer: &mut esp_radio::wifi::sniffer::Sniffer,
+    mac_addr: &[u8],
+    data: &[u8],
+) -> Result<(), alloc::string::String> {
+    const HEADER_SIZE: usize = 24 + 8;
+
+    let mac = mac_addr
+        .try_into()
+        .map_err(|err| alloc::format!("Unexpected MAC address size: {err}"))?;
+
+    // assemble frame
+    let mut frame_buf = alloc::vec::Vec::with_capacity(HEADER_SIZE + data.len());
+    frame_buf.extend_from_slice(&DataFrameHeader::new_80211p(mac).to_binary());
+    frame_buf.extend_from_slice(&LlcHeader::new_80211p().to_binary());
+    frame_buf.extend_from_slice(data);
+
+    // send
+    sniffer
+        .send_raw_frame(true, &frame_buf, true)
+        .map_err(|err| alloc::format!("Failed to send 802.11p frame: {err:?}"))
+}
+
+/// IEEE 802.11p frame header
+#[derive(Debug, Default)]
+struct DataFrameHeader {
+    /// byte 0: subtype in upper nibble, type in lower nibble
+    /// "normal" data frame: 0x08, QoS data frame: 0x88
+    pub type_and_subtype: u8,
+    /// byte 1: frame contol field, 0x00 for 802.11p
+    pub fcf_flags: u8,
+    /// byte 2..3: duration in micros, usually 0x0000 for 802.11p (toDS = 0, fromDS = 0)
+    pub duration: u16,
+    /// byte 4..9: receiver/ destination for 802.11p
+    pub address_1: [u8; 6],
+    /// byte 10..15: transmitter/ source for 802.11p
+    pub address_2: [u8; 6],
+    /// byte 16..21: BSSID for 802.11p
+    pub address_3: [u8; 6],
+    /// byte 22..24: upper 12 bits: seq. no, lower 4 bits: fragment no
+    pub sequence_control: u16,
+    // Note: address 4 is not used in 802.11p
+    // pub qos: Option<[u8; 2]>, // QoS frames are supported by radio library
+    // Note: 802.11p does not use HT mode(s)
+}
+
+impl DataFrameHeader {
+    const BCAST_MAC: [u8; 6] = [0xFF; 6];
+
+    /// Create an 802.11p (non-QoS) data frame header with a source MAC address
+    pub(crate) fn new_80211p(source_mac: &[u8; 6]) -> Self {
+        Self {
+            type_and_subtype: 0x08,
+            address_1: Self::BCAST_MAC,
+            address_2: *source_mac,
+            address_3: Self::BCAST_MAC,
+            ..Default::default()
+        }
+    }
+
+    pub(crate) fn to_binary(&self) -> [u8; 24] {
+        let mut buf = [0u8; 24];
+
+        buf[0] = self.type_and_subtype;
+
+        buf[1] = self.fcf_flags;
+
+        Self::write_u16(&mut buf, 2, self.duration);
+        Self::write_mac_addr(&mut buf, 4, &self.address_1);
+        Self::write_mac_addr(&mut buf, 10, &self.address_2);
+        Self::write_mac_addr(&mut buf, 16, &self.address_3);
+        Self::write_u16(&mut buf, 22, self.sequence_control);
+
+        buf
+    }
+
+    fn write_u16(buf: &mut [u8; 24], offset: usize, data: u16) {
+        for (idx, byte) in data.to_be_bytes().iter().enumerate() {
+            buf[idx + offset] = *byte;
+        }
+    }
+
+    fn write_mac_addr(buf: &mut [u8; 24], offset: usize, data: &[u8; 6]) {
+        for (idx, byte) in data.iter().enumerate() {
+            buf[idx + offset] = *byte;
+        }
+    }
+}
+
+/// IEEE 802.11p LLC header
+#[derive(Debug, Default)]
+struct LlcHeader {
+    /// byte 0: SNAP (0xaa) in 802.11p
+    pub dsap: u8, // SNAP in
+    /// byte 1: SNAP (0xaa) in 802.11p
+    pub lsap: u8, // SNAP in
+    /// byte 2: SNAP (0xaa) in 802.11p
+    pub control_1: u8, // 0x03
+    // Note: optional second control byte not used in 802.11p
+
+    // SNAP fields
+    /// set to 0 since ethertype is used for protocol ID in 802.11p
+    pub oui: [u8; 3],
+    /// ethertype GeoNetworking (0x8947) in 802.11p
+    pub protocol_id: u16,
+}
+
+impl LlcHeader {
+    pub(crate) fn new_80211p() -> Self {
+        Self {
+            dsap: 0xaa,
+            lsap: 0xaa,
+            control_1: 0x03,
+            oui: [0; 3],
+            protocol_id: 0x8947,
+        }
+    }
+
+    pub(crate) fn to_binary(&self) -> [u8; 8] {
+        let mut buf: [u8; 8] = [
+            self.dsap,
+            self.lsap,
+            self.control_1,
+            0x00,
+            0x00,
+            0x00,
+            0x00,
+            0x00,
+        ];
+
+        buf[3] = self.oui[0];
+        buf[4] = self.oui[1];
+        buf[5] = self.oui[2];
+
+        buf[6] = self.protocol_id.to_be_bytes()[0];
+        buf[7] = self.protocol_id.to_be_bytes()[1];
+
+        buf
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use super::*;
+
+    #[test]
+    fn data_frame_test() {
+        // build a typical IEEE 802.11p frame
+        const OWN_MAC: [u8; 6] = [0x12, 0x34, 0x56, 0x78, 0xab, 0xcd];
+        const REF_HEADER: [u8; 24] = [
+            0x08, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x12, 0x34, 0x56, 0x78,
+            0xab, 0xcd, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x00, 0x00,
+        ];
+
+        let frame = DataFrameHeader::new_80211p(&OWN_MAC);
+
+        assert_eq!(0x08, frame.type_and_subtype); // data frame, subtype 0
+        assert_eq!(0x0000, frame.fcf_flags);
+        assert_eq!(0x0000, frame.duration);
+        assert_eq!([0xFF; 6], frame.address_1);
+        assert_eq!(OWN_MAC, frame.address_2);
+        assert_eq!([0xFF; 6], frame.address_3);
+        assert_eq!(0x0000, frame.sequence_control);
+
+        assert_eq!(REF_HEADER, frame.to_binary());
+    }
+
+    #[test]
+    fn llc_test() {
+        // build a typical IEEE 802.11p LLC header
+        const REF_HEADER: [u8; 8] = [0xaa, 0xaa, 0x03, 0x00, 0x00, 0x00, 0x89, 0x47];
+
+        let llc = LlcHeader::new_80211p();
+
+        assert_eq!(0xaa, llc.dsap);
+        assert_eq!(0xaa, llc.lsap);
+        assert_eq!(0x03, llc.control_1);
+        assert_eq!([0x00; 3], llc.oui);
+        assert_eq!(0x8947, llc.protocol_id);
+
+        assert_eq!(REF_HEADER, llc.to_binary());
+    }
+}

src/rx/mod.rs

@@ -0,0 +1,36 @@
+//! V2X Reception Utilities
+
+/// Determines if the WiFi packet is a broadcast data frame
+///
+/// # Errors
+/// Returns a human-readable string, if data contains unexpected values
+pub fn is_broadcast_frame(
+    frame: &esp_radio::wifi::sniffer::PromiscuousPkt<'_>,
+) -> Result<bool, alloc::string::String> {
+    // Ignore frames with errors and non-data frames
+    if frame.rx_cntl.rx_state != 0 {
+        return Err(alloc::format!(
+            "Received frame has RX error: {}",
+            frame.rx_cntl.rx_state
+        ));
+    }
+    if !crate::radio::PromiscuousPktType::Data.matches(frame.frame_type) {
+        return Ok(false);
+    }
+
+    // Ignore non-broadcast frames
+    if frame.len < (4 + 6) {
+        return Err(alloc::format!(
+            "Received frame too small to be a valid broadcast frame: {} bytes",
+            frame.len
+        ));
+    }
+    let dest_mac = &frame.data[4..10];
+    if dest_mac != [0xff; 6] {
+        Err(alloc::format!(
+            "Received frame is not broadcast frame: Dest MAC {dest_mac:02x?}"
+        ))
+    } else {
+        Ok(true)
+    }
+}

src/tx/gn.rs

@@ -0,0 +1,111 @@
+//! Geonetworking utilities
+
+use c_its_parser::gn as geonetworking;
+
+#[allow(unused)]
+/// Creates a Single-Hop Broadcast (SHB) Extended Header from parts
+///
+/// # Errors
+/// Returns a human-readable error description if values are out of range
+pub fn make_shb_eh(
+    address: [u8; 6],
+    station_type: geonetworking::en302636_4_1::StationType,
+    own_position: &crate::PosVel,
+    time: chrono::DateTime<chrono::Utc>,
+) -> Result<geonetworking::en302636_4_1::ExtendedHeader, alloc::string::String> {
+    let source_position_vector = make_lpv(address, station_type, own_position, time)?;
+
+    Ok(geonetworking::en302636_4_1::ExtendedHeader::SHB(
+        geonetworking::en302636_4_1::SingleHopBroadcast {
+            source_position_vector,
+            media_dependent_data: [0; 4],
+        },
+    ))
+}
+
+#[allow(unused)]
+/// Creates a Topo-Scoped Broadcast (TSB) Extended Header from parts
+///
+/// # Errors
+/// Returns a human-readable error description if values are out of range
+pub fn make_tsb_eh(
+    address: [u8; 6],
+    station_type: geonetworking::en302636_4_1::StationType,
+    own_position: &crate::PosVel,
+    time: chrono::DateTime<chrono::Utc>,
+    sequence_number: u16,
+) -> Result<geonetworking::en302636_4_1::ExtendedHeader, alloc::string::String> {
+    let source_position_vector = make_lpv(address, station_type, own_position, time)?;
+
+    Ok(geonetworking::en302636_4_1::ExtendedHeader::TSB(
+        geonetworking::en302636_4_1::TopologicallyScopedBroadcast::new(
+            sequence_number,
+            source_position_vector,
+        ),
+    ))
+}
+
+// #[allow(unused)]
+// /// Creates a Geo-Broadcast Extended Header
+// ///
+// /// # Panics
+// /// Can't panic in practice b/c angle is zero
+// #[must_use]
+// pub fn make_gbc_eh(
+//     address: [u8; 6],
+//     station_type: geonetworking::en302636_4_1::StationType,
+//     own_position: &crate::PosVel,
+//     time: chrono::DateTime<chrono::Utc>,
+//     target_pos: geo_types::Point,
+//     radius_m: u16,
+//     sequence_number: u16,
+// ) -> geonetworking::en302636_4_1::ExtendedHeader {
+//     let source_position_vector = make_lpv(address, station_type, own_position, time);
+//     #[allow(clippy::cast_possible_truncation)]
+//     let latitude_deg = target_pos.x() as f32;
+//     #[allow(clippy::cast_possible_truncation)]
+//     let longitude_deg = target_pos.y() as f32;
+
+//     geonetworking::en302636_4_1::ExtendedHeader::GBC(
+//         geonetworking::en302636_4_1::GeoBroadcast::try_from_values(
+//             sequence_number,
+//             source_position_vector,
+//             latitude_deg,
+//             longitude_deg,
+//             radius_m,
+//             0,
+//             0,
+//         )
+//         .expect("Failed to create circular GBC"),
+//     )
+// }
+
+/// Creates a Long Position Vector from parts
+///
+/// # Errors
+/// Returns a human-readable error description if values are out of range
+pub fn make_lpv(
+    address: [u8; 6],
+    station_type: geonetworking::en302636_4_1::StationType,
+    own_position: &crate::PosVel,
+    time: chrono::DateTime<chrono::Utc>,
+) -> Result<geonetworking::en302636_4_1::LongPositionVector, alloc::string::String> {
+    let timestamp_its = c_its_parser::time_utils::TimestampIts::from(time);
+    #[allow(clippy::cast_possible_truncation)]
+    let latitude_deg = own_position.position.y() as f32;
+    #[allow(clippy::cast_possible_truncation)]
+    let longitude_deg = own_position.position.x() as f32;
+    let speed_mps = own_position.speed_mps.unwrap_or_default();
+    let heading_deg = own_position.heading_deg.unwrap_or_default();
+
+    geonetworking::en302636_4_1::LongPositionVector::try_from_values(
+        geonetworking::en302636_4_1::Address::new(false, station_type, address),
+        timestamp_its.0,
+        latitude_deg,
+        longitude_deg,
+        true,
+        speed_mps,
+        heading_deg,
+    )
+    .map_err(|err| alloc::format!("LPV invalid input: {err}"))
+}

src/tx/mod.rs

@@ -0,0 +1,164 @@
+//! V2X Transmission Utilities
+
+use alloc::vec::Vec;
+
+use c_its_parser::gn as geonetworking;
+
+pub mod gn;
+
+/// Interface for ITS Payloads inside a Geonetworking header
+pub trait GnItsPayload {
+    // common GN parameters
+    const LIFETIME_MILLIS: u32 = 60_000; // itsGnDefaultPacketLifetime is 60 seconds according to ETSI EN 302 636-4-1 V1.4.1
+
+    // ---------------------------------------------
+    // methods to build a GN packet with ITS payload
+    // ---------------------------------------------
+
+    /// Builds the [`geonetworking::en302636_4_1::ExtendedHeader`] and additional information for the ITS message
+    ///
+    /// Output:
+    /// - Extended header
+    /// - Area type (when using GAC or GBC)
+    /// - hop limit
+    ///
+    /// Note: Make sure to increase the sequence number on multi-hop packets.
+    ///
+    /// # Errors
+    /// Returns a human-readable error description if values are out of range
+    fn make_eh(
+        &self,
+        address: [u8; 6],
+        own_position: &crate::PosVel,
+        time: chrono::DateTime<chrono::Utc>,
+        seq_no: &mut u16,
+    ) -> Result<
+        (
+            geonetworking::en302636_4_1::ExtendedHeader,
+            Option<geonetworking::en302636_4_1::AreaType>,
+            u8,
+        ),
+        alloc::string::String,
+    >;
+
+    /// Creates the ITS payload (without BTP header)
+    ///
+    /// # Errors
+    /// Returns a human-readable error description if values are out of range
+    fn make_payload(
+        &self,
+    ) -> Result<(Vec<u8>, c_its_parser::standards::extensions::ItsMessageId), alloc::string::String>;
+
+    // ---------------------------------------------
+    // common methods (with implementation)
+    // ---------------------------------------------
+
+    /// Encodes the GN packet
+    ///
+    /// # Errors
+    /// Returns a human-readable error description if values are out of range
+    fn encode_packet(
+        &self,
+        address: [u8; 6],
+        own_position: &crate::PosVel,
+        time: chrono::DateTime<chrono::Utc>,
+        is_mobile: bool,
+        seq_no: &mut u16,
+    ) -> Result<Vec<u8>, alloc::string::String> {
+        use geonetworking::Encode as _;
+
+        // Build payload (including BTP header)
+        let (mut its_payload, msg_type) = self.make_payload()?;
+        let mut payload = make_btp_b(msg_type).encode()?;
+
+        payload.append(&mut its_payload);
+
+        #[allow(clippy::cast_possible_truncation)]
+        let payload_length = (payload.len()) as u16;
+
+        // get extended header (depending on message type and sometimes content as well)
+        let (eh, area_type, maximum_hop_limit) =
+            self.make_eh(address, own_position, time, seq_no)?;
+
+        // Build GN headers
+        let traffic_class = geonetworking::en302636_4_1::TrafficClass::try_new(
+            false,
+            false,
+            make_traffic_class(msg_type),
+        )
+        .map_err(|err| alloc::format!("Failed to create TrafficClass: {err:?}"))?;
+        let common = geonetworking::en302636_4_1::CommonHeader::from_values(
+            geonetworking::en302636_4_1::NextAfterCommon::BTPB,
+            geonetworking::en302636_4_1::HeaderType::new_from(&eh, area_type)?,
+            traffic_class,
+            is_mobile,
+            payload_length,
+            maximum_hop_limit,
+        );
+
+        let remaining_hop_limit = maximum_hop_limit;
+        let basic = geonetworking::en302636_4_1::BasicHeader::try_new(
+            1,
+            geonetworking::en302636_4_1::NextAfterBasic::CommonHeader,
+            geonetworking::en302636_4_1::Lifetime::from_milliseconds(Self::LIFETIME_MILLIS),
+            remaining_hop_limit,
+        )
+        .map_err(|err| alloc::format!("Failed to create BasicHeader: {err}"))?;
+
+        // Assemble and encode packet
+        let packet = geonetworking::Packet::Unsecured {
+            basic,
+            common,
+            extended: Some(eh),
+            payload: &payload,
+        };
+
+        packet
+            .encode_to_vec()
+            .map_err(|err| alloc::format!("Failed to encode GN packet: {err:?}"))
+    }
+}
+
+/// Creates a BTP-B header based on the ITS message ID (message type)
+///
+/// Port numbers and destination port info according to ETSI TS 103 248
+fn make_btp_b(
+    msg_type: c_its_parser::standards::extensions::ItsMessageId,
+) -> c_its_parser::transport::TransportHeader {
+    let (destination_port, destination_port_info) = match msg_type {
+        c_its_parser::standards::extensions::ItsMessageId::Denm => (2002, 0),
+        c_its_parser::standards::extensions::ItsMessageId::Cam => (2001, 0),
+        c_its_parser::standards::extensions::ItsMessageId::Mapem => (2003, 0),
+        c_its_parser::standards::extensions::ItsMessageId::Spatem => (2004, 0),
+        c_its_parser::standards::extensions::ItsMessageId::Saem => (2005, 0),
+        c_its_parser::standards::extensions::ItsMessageId::Ivim => (2006, 0),
+        c_its_parser::standards::extensions::ItsMessageId::Srem => (2007, 0),
+        c_its_parser::standards::extensions::ItsMessageId::Ssem => (2008, 0),
+        c_its_parser::standards::extensions::ItsMessageId::Cpm => (2009, 0),
+        c_its_parser::standards::extensions::ItsMessageId::Poi => (2010, 0),
+        c_its_parser::standards::extensions::ItsMessageId::EvRsr => (2012, 0),
+        c_its_parser::standards::extensions::ItsMessageId::Rtcmem => (2013, 0),
+        _ => (0, 0), // no information found for the subsequent types
+    };
+
+    c_its_parser::transport::TransportHeader::BtpB(c_its_parser::transport::BasicTransportBHeader {
+        destination_port,
+        destination_port_info,
+    })
+}
+
+/// Creates a traffic class ID based on the ITS message ID (message type)
+fn make_traffic_class(msg_type: c_its_parser::standards::extensions::ItsMessageId) -> u8 {
+    #[allow(clippy::match_same_arms)]
+    match msg_type {
+        c_its_parser::standards::extensions::ItsMessageId::Denm => 1,
+        c_its_parser::standards::extensions::ItsMessageId::Cam => 2,
+        c_its_parser::standards::extensions::ItsMessageId::Mapem => 3, // from C-Roads RS_RSP_063(1)
+        c_its_parser::standards::extensions::ItsMessageId::Spatem => 3, // from C-Roads RS_RSP_063(1)
+        c_its_parser::standards::extensions::ItsMessageId::Ivim => 3, // from C-Roads RS_RSP_063(1)
+        c_its_parser::standards::extensions::ItsMessageId::Srem => 2, // from C-Roads RS_RSP_063(1)
+        c_its_parser::standards::extensions::ItsMessageId::Ssem => 2, // from C-Roads RS_RSP_063(1)
+        c_its_parser::standards::extensions::ItsMessageId::Rtcmem => 3, // CSP_MaxPrio=252 -> 3
+        _ => 3, // fall-back to lowest priority
+    }
+}