lin-bus 0.4.0

//! LIN bus frame definitions

use crate::ldf::NodeAttributes;
use bitfield::BitRange;
use byteorder::{ByteOrder, LittleEndian};
use core::mem::size_of;
use num_traits::{PrimInt, Unsigned};

/// Protected ID which is a 6 bit ID with two parity bits
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
#[repr(transparent)]
pub struct PID(u8);

impl PID {
    /// Creates a new PID object with given PID
    pub const fn new(pid: u8) -> PID {
        // check that the given PID has valid parity bits
        let correct_pid = PID::from_id(pid & 0b0011_1111);
        assert!(correct_pid.0 == pid, "Invalid PID");
        correct_pid
    }

    /// Calculate the PID from an ID.
    /// P0 = ID0 ⊕ ID1 ⊕ ID2 ⊕ ID4
    /// P1 = ¬(ID1 ⊕ ID3 ⊕ ID4 ⊕ ID5)
    pub const fn from_id(id: u8) -> PID {
        assert!(id < 64, "ID must be less than 64");
        // count parity bits and check if they are even odd
        let p0 = (id & 0b1_0111).count_ones() as u8 & 0b1;
        let p1 = ((id & 0b11_1010).count_ones() as u8 + 1) & 0b1;
        PID(id | (p0 << 6u8) | (p1 << 7u8))
    }

    /// Return the contained PID
    pub const fn get(self) -> u8 {
        self.0
    }

    /// Return the contained ID
    pub const fn get_id(self) -> u8 {
        self.0 & 0b0011_1111
    }

    /// Return if the associated frame uses the classic checksum (diagnostic IDs 60 and 61 or
    /// special use IDs 62, 63)
    pub const fn uses_classic_checksum(self) -> bool {
        self.get_id() >= 60
    }
}

/// Calculate the LIN V2.1 "enhanced" checksum. It is defined as "The inverted eight bit sum with
/// carry. Eight bit sum with carry is equivalent to sum all values and subtract 255 every time the
/// sum is greater or equal to 256"
pub fn checksum(pid: PID, data: &[u8]) -> u8 {
    let sum = data.iter().fold(u16::from(pid.0), |sum, v| {
        let sum = sum + u16::from(*v);
        if sum >= 256 {
            sum - 255
        } else {
            sum
        }
    });
    !(sum as u8)
}

/// Calculate the LIN V1.3 "classic" checksum. It is defined as "Checksum calculation over the data
/// bytes only"
pub fn classic_checksum(data: &[u8]) -> u8 {
    checksum(PID(0u8), data)
}

#[derive(Debug, Eq, PartialEq)]
pub struct Frame {
    pub(crate) pid: PID,
    pub(crate) buffer: [u8; 9],
    pub(crate) data_length: usize,
}

impl Frame {
    /// Creates a LIN frame from the PID and data. Calculates and adds checksum accordingly
    pub fn from_data(pid: PID, data: &[u8]) -> Frame {
        assert!(data.len() <= 8, "Maximum data is 8 bytes");
        let mut buffer = [0u8; 9];
        buffer[0..data.len()].clone_from_slice(data);
        buffer[data.len()] = {
            if pid.uses_classic_checksum() {
                classic_checksum(&buffer[0..data.len()])
            } else {
                checksum(pid, &buffer[0..data.len()])
            }
        };
        Frame {
            pid,
            buffer,
            data_length: data.len(),
        }
    }

    /// Access the data from the frame
    pub fn get_data(&self) -> &[u8] {
        &self.buffer[0..self.data_length]
    }

    /// Decode frame data
    pub fn decode<T>(&self, offset: usize, length: usize) -> T
    where
        T: PrimInt + Unsigned,
        u64: BitRange<T>,
    {
        assert!(
            (offset + length) <= self.data_length * 8,
            "Not enough data available"
        );
        assert!(length <= size_of::<T>() * 8, "Output type not big enough");

        let num = LittleEndian::read_u64(&self.buffer[0..8]);
        num.bit_range(offset + length - 1, offset)
    }

    /// Get the checksum from the frame
    pub fn get_checksum(&self) -> u8 {
        self.buffer[self.data_length]
    }

    /// Get the PID from the frame
    pub fn get_pid(&self) -> PID {
        self.pid
    }

    /// Get the serialized bytes to write to the driver
    pub fn get_data_with_checksum(&self) -> &[u8] {
        &self.buffer[0..=self.data_length]
    }
}

/// Implements the transport layer of LIN. The units that are transported in a transport layer
/// frame are called PDU (Packet Data Unit)
pub mod transport {
    use super::{Frame, PID};

    /// NAD is the address of the slave node being addressed in a request, i.e. only slave nodes
    /// have an address. NAD is also used to indicate the source of a response.
    #[derive(Copy, Clone, Debug, PartialEq, Eq)]
    #[repr(transparent)]
    pub struct NAD(pub u8);

    /// The PCI (Protocol Control Information) contains the transport layer flow control
    /// information.
    #[derive(Copy, Clone, Debug, PartialEq, Eq)]
    #[repr(transparent)]
    pub struct PCI(u8);

    /// Type of the `PCI` byte
    #[derive(Copy, Clone, Debug, PartialEq, Eq)]
    pub enum PCIType {
        /// Single Frame
        SF = 0,
        /// First Frame. Start of a multi frame message.
        FF = 1,
        /// Consecutive Frame.
        CF = 2,
        /// Invalid PCIType
        Invalid,
    }

    impl PCI {
        /// Create a `PCI` with type `PCIType::SF` and the given length
        pub const fn new_sf(length: u8) -> PCI {
            assert!(length <= 6, "Maximum length for single frame is 6");
            PCI(length)
        }

        /// Get the `PCIType` of the PCI
        pub const fn get_type(self) -> PCIType {
            match self.0 >> 4 {
                0 => PCIType::SF,
                1 => PCIType::FF,
                2 => PCIType::CF,
                _ => PCIType::Invalid,
            }
        }

        /// Get the length field of the `PCI`
        pub const fn get_length(self) -> u8 {
            self.0 & 0x0F
        }
    }

    /// The Service Identifier (SID) specifies the request that shall be performed by the slave
    /// node addressed.
    #[derive(Copy, Clone, Debug, PartialEq, Eq)]
    #[repr(transparent)]
    pub struct SID(pub u8);

    /// The Response Service Identifier (RSID) specifies the contents of the response.
    #[derive(Copy, Clone, Debug, PartialEq, Eq)]
    #[repr(transparent)]
    pub struct RSID(pub u8);

    /// Create a single frame (CF) PDU
    pub fn create_single_frame(pid: PID, nad: NAD, sid: SID, data: &[u8]) -> Frame {
        assert!(
            !data.is_empty() && data.len() <= 5,
            "A single frame must contain between 0 and 5 bytes"
        );
        // If a PDU is not completely filled the unused bytes shall be filled with 0xFF.
        let mut frame_data = [0xFFu8; 8];
        frame_data[0] = nad.0;
        frame_data[1] = PCI::new_sf(data.len() as u8 + 1).0;
        frame_data[2] = sid.0;
        frame_data[3..data.len() + 3].clone_from_slice(data);
        Frame::from_data(pid, &frame_data)
    }
}

/// Implements the LIN diagnostics methods.
pub mod diagnostic {
    use super::transport::{create_single_frame, NAD, SID};
    use super::{ByteOrder, Frame, LittleEndian, PID};

    pub const MASTER_REQUEST_FRAME_ID: u8 = 0x3C;
    pub const SLAVE_RESPONSE_FRAME_ID: u8 = 0x3D;

    pub const MASTER_REQUEST_FRAME_PID: PID = PID::from_id(0x3C);
    pub const SLAVE_RESPONSE_FRAME_PID: PID = PID::from_id(0x3D);

    pub const READ_BY_IDENTIFIER_SID: SID = SID(0xB2);

    #[repr(u8)]
    /// Identifiers used for the Read by identifer
    pub enum Identifier {
        /// See also `ProductId`
        LINProductIdentification,
        /// See also `SerialNumber`
        SerialNumber,
        /// User defined range 32..=63
        UserDefined(u8),
        /// Reserved range 2..=31 and 64..=255
        Reserved(u8),
    }

    impl From<u8> for Identifier {
        fn from(byte: u8) -> Identifier {
            match byte {
                0 => Identifier::LINProductIdentification,
                1 => Identifier::SerialNumber,
                b @ 32..=63 => Identifier::UserDefined(b),
                b => Identifier::Reserved(b),
            }
        }
    }

    impl From<Identifier> for u8 {
        fn from(identifier: Identifier) -> u8 {
            match identifier {
                Identifier::LINProductIdentification => 0,
                Identifier::SerialNumber => 1,
                Identifier::UserDefined(b) => b,
                Identifier::Reserved(b) => b,
            }
        }
    }

    /// Holds the LIN slave node product identification
    #[derive(Copy, Clone, Debug, PartialEq, Eq)]
    pub struct ProductId {
        pub supplier_id: u16,
        pub function_id: u16,
        pub variant: u8,
    }

    impl From<&[u8]> for ProductId {
        fn from(data: &[u8]) -> ProductId {
            assert!(data.len() >= 5, "We require at least 4 data bytes");
            ProductId {
                supplier_id: LittleEndian::read_u16(&data[0..2]),
                function_id: LittleEndian::read_u16(&data[2..4]),
                variant: data[4],
            }
        }
    }

    #[derive(Copy, Clone, Debug, PartialEq, Eq)]
    #[repr(transparent)]
    pub struct SerialNumber(pub u32);

    impl From<&[u8]> for SerialNumber {
        fn from(data: &[u8]) -> SerialNumber {
            assert!(data.len() >= 4, "We require at least 4 data bytes");
            SerialNumber(LittleEndian::read_u32(data))
        }
    }

    /// Create a read by identifier `Frame` from `NodeAttributes`
    pub fn create_read_by_identifier_frame_from_node_attributes(
        node_attributes: super::NodeAttributes,
        identifier: Identifier,
    ) -> Frame {
        create_read_by_identifier_frame(
            node_attributes.initial_nad,
            identifier,
            node_attributes.product_id.supplier_id,
            node_attributes.product_id.function_id,
        )
    }

    /// Create a read by identifier frame
    pub fn create_read_by_identifier_frame(
        nad: NAD,
        identifier: Identifier,
        supplier_id: u16,
        function_id: u16,
    ) -> Frame {
        create_single_frame(
            MASTER_REQUEST_FRAME_PID,
            nad,
            READ_BY_IDENTIFIER_SID,
            &[
                identifier.into(),
                (supplier_id & 0xFF) as u8,
                (supplier_id >> 8) as u8,
                (function_id & 0xFF) as u8,
                (function_id >> 8) as u8,
            ],
        )
    }

    pub fn create_read_lin_product_identification_frame(
        node_attributes: super::NodeAttributes,
    ) -> Frame {
        create_read_by_identifier_frame_from_node_attributes(
            node_attributes,
            Identifier::LINProductIdentification,
        )
    }

    pub fn create_read_serial_number_frame(node_attributes: super::NodeAttributes) -> Frame {
        create_read_by_identifier_frame_from_node_attributes(
            node_attributes,
            Identifier::SerialNumber,
        )
    }
}

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

    struct CheckSumTestData<'a> {
        pid: PID,
        data: &'a [u8],
        checksum: u8,
    }

    #[test]
    fn test_enhanced_checksum() {
        let test_data = [
            CheckSumTestData {
                pid: PID(0xDD),
                data: &[0x01],
                checksum: 0x21,
            },
            CheckSumTestData {
                pid: PID(0x4A),
                data: &[0x55, 0x93, 0xE5],
                checksum: 0xE6,
            },
            CheckSumTestData {
                pid: PID(0xBF),
                data: &[0x40, 0xFF],
                checksum: 0x00,
            },
        ];
        for d in &test_data {
            assert_eq!(d.checksum, checksum(d.pid, d.data));
        }
    }

    #[test]
    fn test_classic_checksum() {
        let test_data = [
            CheckSumTestData {
                pid: PID::from_id(0x3C),
                data: &[0x01],
                checksum: 0xFE,
            },
            CheckSumTestData {
                pid: PID::from_id(0x3D),
                data: &[0x01],
                checksum: 0xFE,
            },
            CheckSumTestData {
                pid: PID::from_id(0x3d),
                data: &[0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08],
                checksum: 0xDB,
            },
        ];
        for d in &test_data {
            assert_eq!(d.checksum, classic_checksum(d.data));
        }
    }

    #[test]
    fn test_pid_new() {
        let test_data = [
            (0x64, PID::new(0x64)),
            (0xCA, PID::new(0xCA)),
            (0x80, PID::new(0x80)),
            (0xC1, PID::new(0xC1)),
            (0x47, PID::new(0x47)),
            (0x61, PID::new(0x61)),
        ];

        for d in &test_data {
            assert_eq!(d.0, d.1.get());
        }
    }

    #[test]
    #[should_panic]
    fn test_invalid_pid_new() {
        PID::new(0x07);
    }

    #[test]
    fn test_pid_from_id() {
        let test_data = [
            (0, PID(0x80)),
            (1, PID(0xC1)),
            (2, PID(0x42)),
            (25, PID(0x99)),
            (27, PID(0x5B)),
            (29, PID(0xDD)),
        ];

        for d in &test_data {
            let pid = PID::from_id(d.0);
            assert_eq!(pid, d.1);
            assert_eq!(pid.get_id(), d.0);
        }
    }

    #[test]
    fn test_id_uses_classic_checksum() {
        let test_ids: &[u8] = &[0, 1, 59, 60, 63];

        for i in test_ids {
            assert_eq!(PID::from_id(*i).uses_classic_checksum(), *i >= 60);
        }
    }

    #[test]
    #[should_panic]
    fn test_pid_from_id_panic() {
        PID::from_id(64);
    }

    #[test]
    fn test_pci() {
        let pci = PCI::new_sf(5);
        assert_eq!(pci.get_type(), PCIType::SF);
        assert_eq!(pci.get_length(), 5);
    }

    #[test]
    fn test_transport_frame() {
        struct TestData {
            pid: PID,
            nad: transport::NAD,
            sid: transport::SID,
            data: &'static [u8],
            frame_data: [u8; 8],
        }
        let test_data = [
            TestData {
                pid: diagnostic::MASTER_REQUEST_FRAME_PID,
                nad: transport::NAD(0x10),
                sid: transport::SID(0xB2),
                data: &[0x01, 0xB3, 0x00, 0x01, 0x10],
                frame_data: [0x10, 0x06, 0xB2, 0x01, 0xB3, 0x00, 0x01, 0x10],
            },
            TestData {
                pid: diagnostic::SLAVE_RESPONSE_FRAME_PID,
                nad: transport::NAD(0x10),
                sid: transport::SID(0xB2),
                data: &[0x01],
                frame_data: [0x10, 0x02, 0xB2, 0x01, 0xFF, 0xFF, 0xFF, 0xFF],
            },
        ];

        for d in &test_data {
            let frame = transport::create_single_frame(d.pid, d.nad, d.sid, d.data);
            assert_eq!(frame.get_pid(), d.pid);
            assert_eq!(frame.get_data(), d.frame_data);
            assert_eq!(frame.data_length, 8);
        }
    }

    #[test]
    #[should_panic]
    fn test_transport_frame_without_data() {
        transport::create_single_frame(
            PID::from_id(0x1),
            transport::NAD(0x2),
            transport::SID(0x03),
            &[],
        );
    }

    #[test]
    #[should_panic]
    fn test_transport_frame_with_too_much_data() {
        transport::create_single_frame(
            PID::from_id(0x1),
            transport::NAD(0x2),
            transport::SID(0x03),
            &[1, 2, 3, 4, 5, 6],
        );
    }

    #[test]
    fn test_create_read_by_identifier_frame() {
        const LIN_ID_SERIAL_REQ_PAYLOAD: &[u8] = &[0x10, 0x06, 0xB2, 0x01, 0xB3, 0x00, 0x01, 0x10];

        let frame = diagnostic::create_read_by_identifier_frame(
            transport::NAD(0x10),
            diagnostic::Identifier::SerialNumber,
            0x00B3,
            0x1001,
        );

        assert_eq!(frame.get_pid(), diagnostic::MASTER_REQUEST_FRAME_PID);
        assert_eq!(frame.get_data(), LIN_ID_SERIAL_REQ_PAYLOAD);
        assert_eq!(frame.data_length, 8);
    }

    #[test]
    fn test_create_read_by_identifier_frame_from_node_attributes() {
        const LIN_ID_SERIAL_REQ_PAYLOAD: &[u8] = &[0x10, 0x06, 0xB2, 0x01, 0xB3, 0x00, 0x01, 0x10];
        let node_attributes = NodeAttributes::with_default_timing(
            transport::NAD(0x10),
            transport::NAD(0x10),
            diagnostic::ProductId {
                supplier_id: 0x00B3,
                function_id: 0x1001,
                variant: 0x00,
            },
        );

        let frame = diagnostic::create_read_by_identifier_frame_from_node_attributes(
            node_attributes,
            diagnostic::Identifier::SerialNumber,
        );
        assert_eq!(frame.get_pid(), diagnostic::MASTER_REQUEST_FRAME_PID);
        assert_eq!(frame.get_data(), LIN_ID_SERIAL_REQ_PAYLOAD);
        assert_eq!(frame.data_length, 8);
    }

    #[test]
    fn test_decode_product_id() {
        let product_id = ProductId {
            supplier_id: 0x00B3,
            function_id: 0x1001,
            variant: 0x01,
        };
        let data = [0xB3, 0x00, 0x01, 0x10, 0x01];

        assert_eq!(product_id, ProductId::from(&data[..]));
    }

    #[test]
    fn test_decode_serial_number() {
        let serial_number = SerialNumber(190200009);
        let data = [0xC9, 0x38, 0x56, 0x0B];
        assert_eq!(serial_number, SerialNumber::from(&data[..]));
    }
}