canopen_rs/

nmt.rs

//! Network Management (NMT) — the node state machine (CiA 301 §7.3).
//!
//! NMT governs a node's lifecycle. A node powers up in *Initialisation*,
//! emits its boot-up message, and autonomously enters *Pre-operational*.
//! From there an NMT master moves it between *Operational* and *Stopped* with
//! node-control commands broadcast on COB-ID `0x000`. Each node reports its
//! current state to the network through the error-control (heartbeat)
//! producer on `0x700 + node`.
//!
//! ```text
//!                    ┌──────────────── reset ◄────────────┐
//!                    ▼                                     │
//!            ┌───────────────┐  boot   ┌──────────────────┴─┐
//!            │ Initialising  ├────────►│  Pre-operational   │
//!            └───────────────┘         └──┬──────────────▲──┘
//!                              start(0x01)│              │enter-preop(0x80)
//!                                         ▼              │
//!                                   ┌─────┴──────────────┴──┐
//!                       ┌──────────►│     Operational       │
//!            start(0x01)│           └─────────┬─────────────┘
//!                       │              stop(0x02)
//!                 ┌─────┴─────┐               ▼
//!                 │  Stopped  │◄──────────────┘
//!                 └───────────┘
//! ```
//!
//! Like the SDO codec, the functions here encode and decode raw CAN *data
//! fields* only; selecting the COB-ID and moving the frame is the transport's
//! job. [`NmtStateMachine`] is the node-side state logic, with no I/O.
//!
//! ```
//! use canopen_rs::nmt::encode_command;
//! use canopen_rs::{NmtCommand, NmtState, NmtStateMachine, NodeId};
//!
//! // Master side: command node 5 to start (enter operational).
//! let frame = encode_command(NmtCommand::StartRemoteNode, NodeId::new(5).unwrap());
//! assert_eq!(frame, [0x01, 0x05]); // [command specifier, target node]
//!
//! // Node side: the guarded state machine.
//! let mut sm = NmtStateMachine::new();
//! assert_eq!(sm.state(), NmtState::Initialising);
//! sm.boot(); // -> pre-operational
//! assert_eq!(sm.apply(NmtCommand::StartRemoteNode), NmtState::Operational);
//! assert_eq!(sm.apply(NmtCommand::ResetNode), NmtState::Initialising);
//! ```

use crate::types::NodeId;
use crate::{Error, Result};

/// COB-ID of the NMT node-control channel (master → nodes): `0x000`.
///
/// This is the highest-priority id on the bus; a single frame can address one
/// node or, with target `0`, every node at once.
pub const NMT_COMMAND_COB_ID: u16 = 0x000;

/// COB-ID base for the error-control (heartbeat / boot-up) channel:
/// `0x700 + node`.
pub const HEARTBEAT_COB_BASE: u16 = 0x700;

/// The COB-ID of a node's heartbeat / boot-up producer channel.
pub const fn heartbeat_cob_id(node: NodeId) -> u16 {
    HEARTBEAT_COB_BASE + node.raw() as u16
}

/// A node's NMT state.
///
/// The discriminant is the value carried in a heartbeat frame (CiA 301
/// §7.2.8.3). [`NmtState::Initialising`] is reported as `0` — the value of a
/// boot-up message, sent once as the node leaves initialisation.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum NmtState {
    /// Initialising (boot-up); reported as `0`.
    Initialising = 0x00,
    /// Stopped: only NMT and error-control are active.
    Stopped = 0x04,
    /// Operational: all communication objects (incl. PDOs) are active.
    Operational = 0x05,
    /// Pre-operational: SDOs active, PDOs inactive.
    PreOperational = 0x7F,
}

impl NmtState {
    /// Decode a heartbeat state byte, ignoring the reserved toggle bit (7).
    ///
    /// Returns [`Error::UnknownState`] for an unrecognised value.
    pub const fn from_wire(byte: u8) -> Result<Self> {
        Ok(match byte & 0x7F {
            0x00 => NmtState::Initialising,
            0x04 => NmtState::Stopped,
            0x05 => NmtState::Operational,
            0x7F => NmtState::PreOperational,
            _ => return Err(Error::UnknownState),
        })
    }
}

/// An NMT node-control command from the master (CiA 301 §7.2.8.2).
///
/// The discriminant is the command specifier carried in byte 0 of an
/// `0x000` frame.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum NmtCommand {
    /// Start remote node → *Operational*.
    StartRemoteNode = 0x01,
    /// Stop remote node → *Stopped*.
    StopRemoteNode = 0x02,
    /// Enter pre-operational → *Pre-operational*.
    EnterPreOperational = 0x80,
    /// Reset node → re-enter *Initialising* (application + communication).
    ResetNode = 0x81,
    /// Reset communication → re-enter *Initialising* (communication only).
    ResetCommunication = 0x82,
}

impl NmtCommand {
    /// Decode a command specifier byte.
    ///
    /// Returns [`Error::UnexpectedCommand`] for an unrecognised specifier.
    pub const fn from_byte(byte: u8) -> Result<Self> {
        Ok(match byte {
            0x01 => NmtCommand::StartRemoteNode,
            0x02 => NmtCommand::StopRemoteNode,
            0x80 => NmtCommand::EnterPreOperational,
            0x81 => NmtCommand::ResetNode,
            0x82 => NmtCommand::ResetCommunication,
            _ => return Err(Error::UnexpectedCommand),
        })
    }
}

/// The 2-byte data field of an NMT node-control frame.
pub type NmtCommandFrame = [u8; 2];

/// The 1-byte data field of a heartbeat / boot-up frame.
pub type HeartbeatFrame = [u8; 1];

/// The boot-up message data field (`0x00`), emitted once when a node leaves
/// initialisation and enters pre-operational.
pub const BOOTUP_FRAME: HeartbeatFrame = [0x00];

/// Encode an NMT node-control frame for `target`.
///
/// Pass [`NodeId::BROADCAST`] to address every node on the bus at once.
pub fn encode_command(command: NmtCommand, target: NodeId) -> NmtCommandFrame {
    [command as u8, target.raw()]
}

/// Decode an NMT node-control frame into `(command, target)`.
///
/// A target byte of `0` decodes to [`NodeId::BROADCAST`]; any other value is a
/// checked device id (`1..=127`), else [`Error::InvalidNodeId`].
pub fn decode_command(frame: &NmtCommandFrame) -> Result<(NmtCommand, NodeId)> {
    let command = NmtCommand::from_byte(frame[0])?;
    let target = if frame[1] == 0 {
        NodeId::BROADCAST
    } else {
        NodeId::new(frame[1])?
    };
    Ok((command, target))
}

/// Encode a heartbeat frame reporting `state`.
pub fn encode_heartbeat(state: NmtState) -> HeartbeatFrame {
    [state as u8]
}

/// Decode a heartbeat frame into the reported [`NmtState`].
pub fn decode_heartbeat(frame: &HeartbeatFrame) -> Result<NmtState> {
    NmtState::from_wire(frame[0])
}

/// The node-side NMT state machine (CiA 301 §7.3.2).
///
/// Holds only the current state and applies the guarded transitions of the
/// diagram above. It performs no I/O: feed it decoded [`NmtCommand`]s and read
/// back the resulting [`NmtState`] to drive heartbeat production and to gate
/// which services (e.g. PDOs) are active.
#[derive(Debug)]
pub struct NmtStateMachine {
    state: NmtState,
}

impl Default for NmtStateMachine {
    fn default() -> Self {
        Self::new()
    }
}

impl NmtStateMachine {
    /// A freshly powered node, in [`NmtState::Initialising`].
    pub const fn new() -> Self {
        Self {
            state: NmtState::Initialising,
        }
    }

    /// The current state.
    pub const fn state(&self) -> NmtState {
        self.state
    }

    /// Complete initialisation: the node enters pre-operational (CiA 301
    /// §7.3.2.1). The caller emits [`BOOTUP_FRAME`] alongside this transition.
    ///
    /// A no-op unless currently initialising.
    pub fn boot(&mut self) -> NmtState {
        if let NmtState::Initialising = self.state {
            self.state = NmtState::PreOperational;
        }
        self.state
    }

    /// Apply an NMT master command, returning the resulting state.
    ///
    /// Transitions are guarded: a reset returns to *Initialising* from any
    /// state, while start/stop/enter-pre-operational are ignored during
    /// initialisation (the node is not yet a network participant) and
    /// otherwise move between the operational states. Repeating a command that
    /// matches the current state is a harmless no-op.
    pub fn apply(&mut self, command: NmtCommand) -> NmtState {
        self.state = match (self.state, command) {
            // Reset re-enters initialisation from any state.
            (_, NmtCommand::ResetNode | NmtCommand::ResetCommunication) => NmtState::Initialising,
            // During initialisation the node ignores operational commands; it
            // leaves this state only via `boot`.
            (NmtState::Initialising, _) => NmtState::Initialising,
            (_, NmtCommand::StartRemoteNode) => NmtState::Operational,
            (_, NmtCommand::StopRemoteNode) => NmtState::Stopped,
            (_, NmtCommand::EnterPreOperational) => NmtState::PreOperational,
        };
        self.state
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    // --- COB-IDs -----------------------------------------------------------
    #[test]
    fn heartbeat_cob_id_follows_convention() {
        assert_eq!(heartbeat_cob_id(NodeId::new(0x05).unwrap()), 0x705);
        assert_eq!(NMT_COMMAND_COB_ID, 0x000);
    }

    // --- Command codec: known-good frames ----------------------------------
    // NMT frames are [command specifier, target node]. Target 0 = all nodes.
    #[test]
    fn start_broadcast_matches_known_frame() {
        assert_eq!(
            encode_command(NmtCommand::StartRemoteNode, NodeId::BROADCAST),
            [0x01, 0x00]
        );
    }

    #[test]
    fn start_single_node_matches_known_frame() {
        let f = encode_command(NmtCommand::StartRemoteNode, NodeId::new(5).unwrap());
        assert_eq!(f, [0x01, 0x05]);
    }

    #[test]
    fn stop_single_node_matches_known_frame() {
        let f = encode_command(NmtCommand::StopRemoteNode, NodeId::new(5).unwrap());
        assert_eq!(f, [0x02, 0x05]);
    }

    #[test]
    fn reset_commands_match_known_frames() {
        let node = NodeId::new(0x7F).unwrap();
        assert_eq!(
            encode_command(NmtCommand::EnterPreOperational, node),
            [0x80, 0x7F]
        );
        assert_eq!(encode_command(NmtCommand::ResetNode, node), [0x81, 0x7F]);
        assert_eq!(
            encode_command(NmtCommand::ResetCommunication, node),
            [0x82, 0x7F]
        );
    }

    #[test]
    fn command_frame_roundtrips() {
        let (cmd, target) = decode_command(&[0x01, 0x05]).unwrap();
        assert_eq!(cmd, NmtCommand::StartRemoteNode);
        assert_eq!(target, NodeId::new(5).unwrap());

        let (cmd, target) = decode_command(&[0x82, 0x00]).unwrap();
        assert_eq!(cmd, NmtCommand::ResetCommunication);
        assert_eq!(target, NodeId::BROADCAST);
    }

    #[test]
    fn decode_rejects_unknown_command() {
        assert_eq!(decode_command(&[0x7E, 0x05]), Err(Error::UnexpectedCommand));
    }

    // --- Heartbeat / boot-up codec: known-good frames ----------------------
    #[test]
    fn heartbeat_states_match_known_frames() {
        assert_eq!(encode_heartbeat(NmtState::Operational), [0x05]);
        assert_eq!(encode_heartbeat(NmtState::Stopped), [0x04]);
        assert_eq!(encode_heartbeat(NmtState::PreOperational), [0x7F]);
        assert_eq!(BOOTUP_FRAME, [0x00]);
    }

    #[test]
    fn heartbeat_decode_ignores_toggle_bit() {
        // Bit 7 is reserved (toggle in node guarding); decoding must mask it.
        assert_eq!(decode_heartbeat(&[0x05]).unwrap(), NmtState::Operational);
        assert_eq!(decode_heartbeat(&[0x85]).unwrap(), NmtState::Operational);
    }

    #[test]
    fn heartbeat_decode_rejects_unknown_state() {
        assert_eq!(decode_heartbeat(&[0x42]), Err(Error::UnknownState));
    }

    // --- State machine -----------------------------------------------------
    #[test]
    fn boots_from_init_to_preoperational() {
        let mut sm = NmtStateMachine::new();
        assert_eq!(sm.state(), NmtState::Initialising);
        assert_eq!(sm.boot(), NmtState::PreOperational);
    }

    #[test]
    fn ignores_operational_commands_while_initialising() {
        let mut sm = NmtStateMachine::new();
        assert_eq!(
            sm.apply(NmtCommand::StartRemoteNode),
            NmtState::Initialising
        );
    }

    #[test]
    fn full_operational_lifecycle() {
        let mut sm = NmtStateMachine::new();
        sm.boot();
        assert_eq!(sm.apply(NmtCommand::StartRemoteNode), NmtState::Operational);
        assert_eq!(
            sm.apply(NmtCommand::EnterPreOperational),
            NmtState::PreOperational
        );
        assert_eq!(sm.apply(NmtCommand::StopRemoteNode), NmtState::Stopped);
        assert_eq!(sm.apply(NmtCommand::StartRemoteNode), NmtState::Operational);
    }

    #[test]
    fn reset_returns_to_initialising_from_any_state() {
        let mut sm = NmtStateMachine::new();
        sm.boot();
        sm.apply(NmtCommand::StartRemoteNode);
        assert_eq!(sm.apply(NmtCommand::ResetNode), NmtState::Initialising);
        // And a fresh boot works again.
        assert_eq!(sm.boot(), NmtState::PreOperational);

        sm.apply(NmtCommand::StartRemoteNode);
        assert_eq!(
            sm.apply(NmtCommand::ResetCommunication),
            NmtState::Initialising
        );
    }

    #[test]
    fn repeated_command_is_idempotent() {
        let mut sm = NmtStateMachine::new();
        sm.boot();
        sm.apply(NmtCommand::StartRemoteNode);
        assert_eq!(sm.apply(NmtCommand::StartRemoteNode), NmtState::Operational);
    }
}