hid_io_protocol/

lib.rs

/* Copyright (C) 2017-2023 by Jacob Alexander
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

// ----- Modules -----

#![no_std]
#![feature(associated_type_defaults)]

pub mod buffer;
pub mod commands;
pub mod test;

// ----- Crates -----

use core::convert::TryFrom;
use core::fmt;
use heapless::Vec;
use num_enum::{IntoPrimitive, TryFromPrimitive};

#[cfg(feature = "defmt")]
use defmt::{error, trace, warn};
#[cfg(not(feature = "defmt"))]
use log::{error, trace, warn};

// ----- Macros -----

#[cfg(not(feature = "server"))]
macro_rules! warn {
    (target: $target:expr, $($arg:tt)+) => {};
    ($($arg:tt)+) => {};
}

#[cfg(not(feature = "server"))]
macro_rules! error {
    (target: $target:expr, $($arg:tt)+) => {};
    ($($arg:tt)+) => {};
}

// ----- Enumerations -----

/// HID-IO Packet Types
///
/// # Remarks
/// Must not be larger than 0x7, 7 is reserved.
#[derive(PartialEq, Eq, Clone, Copy, Debug)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub enum HidIoPacketType {
    /// Data packet
    Data = 0,
    /// Ack packet
    Ack = 1,
    /// Nak packet
    Nak = 2,
    /// Sync packet
    Sync = 3,
    /// Continued packet
    Continued = 4,
    /// No acknowledgement data packet
    NaData = 5,
    /// No acknowledgement continued packet
    NaContinued = 6,
}

#[repr(u32)]
#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Debug, IntoPrimitive, TryFromPrimitive)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
/// Requests for to perform a specific action
pub enum HidIoCommandId {
    SupportedIds = 0x00,
    GetInfo = 0x01,
    TestPacket = 0x02,
    ResetHidIo = 0x03,
    Reserved = 0x04, // ... 0x0F

    GetProperties = 0x10,
    KeyState = 0x11,
    KeyboardLayout = 0x12,
    KeyLayout = 0x13,
    KeyShapes = 0x14,
    LedLayout = 0x15,
    FlashMode = 0x16,
    UnicodeText = 0x17,
    UnicodeState = 0x18,
    HostMacro = 0x19,
    SleepMode = 0x1A,

    KllState = 0x20,
    PixelSetting = 0x21,
    PixelSet1c8b = 0x22,
    PixelSet3c8b = 0x23,
    PixelSet1c16b = 0x24,
    PixelSet3c16b = 0x25,
    DirectSet = 0x26,

    OpenUrl = 0x30,
    TerminalCmd = 0x31,
    GetInputLayout = 0x32,
    SetInputLayout = 0x33,
    TerminalOut = 0x34,

    HidKeyboard = 0x40,
    HidKeyboardLed = 0x41,
    HidMouse = 0x42,
    HidJoystick = 0x43,
    HidSystemCtrl = 0x44,
    HidConsumerCtrl = 0x45,

    ManufacturingTest = 0x50,
    ManufacturingResult = 0x51,

    Unused = 0xFFFF,
}

/// HID-IO Parse Error
///
/// # Remarks
/// thrown when there's an issue processing byte stream.
#[derive(Debug)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub enum HidIoParseError {
    BufferNotReady,
    BufferDataTooSmall(usize),
    InvalidContinuedIdByte(u8),
    InvalidHidIoCommandId(u32),
    InvalidPacketIdWidth(u8),
    InvalidPacketType(u8),
    MissingContinuedIdByte,
    MissingPacketIdWidthByte,
    MissingPacketTypeByte,
    MissingPayloadLengthByte,
    NotEnoughActualBytesPacketId { len: usize, id_width: usize },
    NotEnoughPossibleBytesPacketId { len: u32, id_width: usize },
    PayloadAddFailed(usize),
    SerializationError,
    SerializationFailedResultTooSmall(usize),
    VecAddFailed,
    VecResizeFailed,
}

// ----- Structs -----

/// HID-IO Packet Buffer Struct
///
/// # Remarks
/// Used to store HID-IO data chunks. Will be chunked into individual packets on transmission.
#[repr(C)]
#[derive(PartialEq, Eq, Clone, Debug)]
#[cfg_attr(feature = "defmt", derive(defmt::Format))]
pub struct HidIoPacketBuffer<const H: usize> {
    /// Type of packet (Continued is automatically set if needed)
    pub ptype: HidIoPacketType,
    /// Packet Id
    pub id: HidIoCommandId,
    /// Packet length for serialization (in bytes)
    pub max_len: u32,
    /// Payload data, chunking is done automatically by serializer
    pub data: Vec<u8, H>,
    /// Set False if buffer is not complete, True if it is
    pub done: bool,
}

// ----- Utility Functions -----

/// Determines the packet type from a byte stream
///
/// # Arguments
/// * `packet_data` - Vector of bytes
///
/// # Remarks
/// Uses a packet byte stream to determine the packet type.
/// First three bits of data stream are used (from C-Struct):
///
/// ```c
/// struct HidIo_Packet {
///    HidIo_Packet_Type type:3;
///    ...
/// };
/// ```
pub fn packet_type(packet_data: &[u8]) -> Result<HidIoPacketType, HidIoParseError> {
    let packet_data_len = packet_data.len();

    // Check if the byte stream is large enough
    if packet_data_len < 1 {
        return Err(HidIoParseError::MissingPacketTypeByte);
    }

    // Extract first 3 bits from first byte
    let ptype: u8 = (packet_data[0] & 0xE0) >> 5;

    // Convert to HidIoPacketType enum
    match ptype {
        0 => Ok(HidIoPacketType::Data),
        1 => Ok(HidIoPacketType::Ack),
        2 => Ok(HidIoPacketType::Nak),
        3 => Ok(HidIoPacketType::Sync),
        4 => Ok(HidIoPacketType::Continued),
        5 => Ok(HidIoPacketType::NaData),
        6 => Ok(HidIoPacketType::NaContinued),
        _ => Err(HidIoParseError::InvalidPacketType(ptype)),
    }
}

/// Determines payload of packet from a byte stream
///
/// # Arguments
/// * `packet_data` - Vector of bytes
///
/// # Remarks
/// Uses a packet byte stream to determine payload length.
/// This length does not include the first 2 packet bytes in the overall packet length.
/// The length does include the bytes used for the packet Id.
///
/// ```c
/// struct HidIo_Packet {
///    ... (6 bits)
///    uint8_t           upper_len:2; // Upper 2 bits of length field (generally unused)
///    uint8_t           len;         // Lower 8 bits of length field
///    ...
/// };
/// ```
pub fn payload_len(packet_data: &[u8]) -> Result<u32, HidIoParseError> {
    let packet_data_len = packet_data.len();

    // Check if the byte stream is large enough
    if packet_data_len < 2 {
        return Err(HidIoParseError::MissingPayloadLengthByte);
    }

    // Extract upper_len and len
    let upper_len = u32::from(packet_data[0] & 0x3);
    let len = u32::from(packet_data[1]);

    // Merge
    let payload_len: u32 = (upper_len << 8) | len;

    Ok(payload_len)
}

/// Determines id_width from a byte stream
///
/// # Arguments
/// * `packet_data` - Vector of bytes
///
/// # Remarks
/// Uses a packet byte stream to determine packet id_width.
///
/// ```c
/// struct HidIo_Packet {
///    ... (4 bits)
///    uint8_t           id_width:1;  // 0 - 16bits, 1 - 32bits
///    ...
/// };
/// ```
pub fn packet_id_width(packet_data: &[u8]) -> Result<usize, HidIoParseError> {
    let packet_data_len = packet_data.len();

    // Check if the byte stream is large enough
    if packet_data_len < 2 {
        return Err(HidIoParseError::MissingPacketIdWidthByte);
    }

    // Extract id_width
    match packet_data[0] & 0x08 {
        0x00 => Ok(2), // 16 bit
        0x08 => Ok(4), // 32 bit
        _ => Err(HidIoParseError::InvalidPacketIdWidth(packet_data[0])),
    }
}

/// Determines packet id from a byte stream
///
/// # Arguments
/// * `packet_data` - Vector of bytes
///
/// # Remarks
/// Uses a packet byte stream to determine packet Id.
///
/// ```c
/// struct HidIo_Packet {
///    ... (4 bits)
///    uint8_t           id_width:1;  // 0 - 16bits, 1 - 32bits
///    ... (11 bits)
///    uint16_t/uint32_t id;          // Id field (check id_width to see which struct to use)
///    ...
/// };
/// ```
pub fn packet_id(packet_data: &[u8]) -> Result<u32, HidIoParseError> {
    let packet_data_len = packet_data.len();

    // Extract id_width
    let id_width = packet_id_width(packet_data)?;

    // Make sure there are enough possible bytes
    if payload_len(packet_data)? < id_width as u32 {
        return Err(HidIoParseError::NotEnoughPossibleBytesPacketId {
            len: payload_len(packet_data)?,
            id_width,
        });
    }

    // Make sure there enough actual bytes
    if packet_data_len < id_width + 2 {
        return Err(HidIoParseError::NotEnoughActualBytesPacketId {
            len: packet_data_len,
            id_width,
        });
    }

    // Iterate over bytes, constructing Id of either 16 or 32 bit width
    let mut id: u32 = 0;
    let offset = 2;
    for idx in 0..id_width {
        id |= u32::from(packet_data[offset + idx]) << (idx * 8);
    }

    Ok(id)
}

/// Determines whether there are following continued packets
///
/// # Arguments
/// * `packet_data` - Vector of bytes
///
/// # Remarks
/// Uses a packet byte stream to determine cont field.
///
/// ```c
/// struct HidIo_Packet {
///    ... (3 bits)
///    uint8_t           cont:1;      // 0 - Only packet, 1 continued packet following
///    ...
/// };
/// ```
pub fn continued_packet(packet_data: &[u8]) -> Result<bool, HidIoParseError> {
    let packet_data_len = packet_data.len() as u32;

    // Check if the byte stream is large enough
    if packet_data_len < 1 {
        return Err(HidIoParseError::MissingContinuedIdByte);
    }

    // Extract cont field
    // Determine value
    match packet_data[0] & 0x10 {
        0x10 => Ok(true),
        0x00 => Ok(false),
        _ => Err(HidIoParseError::InvalidContinuedIdByte(packet_data[0])),
    }
}

/// Determines the starting position of the payload data
///
/// # Arguments
/// * `packet_data` - Vector of bytes
///
/// # Remarks
/// Uses a packet byte stream to find payload start.
/// Please note that there may be no payload, or Id.
/// In this case the starting position will be index 2.
pub fn payload_start(packet_data: &[u8]) -> Result<usize, HidIoParseError> {
    // Retrieve id_width
    let id_width = packet_id_width(packet_data)?;

    // Retrieve payload_len, if 0, then return 2 (minimum packet size)
    if payload_len(packet_data)? == 0 {
        return Ok(2);
    }

    // Determine starting position
    Ok(2 + id_width)
}

// ----- Command Utility Functions -----

/// Converts a HID bitmask into an array of byte codes
///
/// # Arguments
/// * `bitmask` - Vector of bytes (each byte is an 8 bit bitmask)
///
/// # Remarks
/// The very first byte in the bitmask represents 0->7 and the final byte ends at 255
/// Opposite of keyboard_vec2bitmask.
/// NOTE: The vector is currently restricted to 32 byte codes
///       technically this could be a maximum of 256, but that
///       is both impractical and unlikely. i.e. we only have 10
///       fingers.
pub fn hid_bitmask2vec(bitmask: &[u8]) -> Result<Vec<u8, 32>, HidIoParseError> {
    let mut data: Vec<u8, 32> = Vec::new();

    // Iterate over each byte of the bitmask adding a code for each found bit
    for (byte_pos, byte) in bitmask.iter().enumerate() {
        // Iterate over each of the bits
        for b in 0..=7 {
            // Check if bit is active, if so use the b position, then add byte_pos
            let active = ((byte >> b) & 0x01) == 0x01;
            if active {
                let code = b + byte_pos * 8;
                if data.push(code as u8).is_err() {
                    return Err(HidIoParseError::VecAddFailed);
                }
            }
        }
    }
    Ok(data)
}

/// Converts a HID byte code array into a bitmask
///
/// # Arguments
/// * `codes` - Vector of bytes (e.g. each byte is a HID keyboard code)
///
/// # Remarks
/// Opposite of keyboard_bitmask2vec.
pub fn hid_vec2bitmask(codes: &[u8]) -> Result<Vec<u8, 32>, HidIoParseError> {
    let mut data: Vec<u8, 32> = Vec::new(); // Maximum of 32 bytes when dealing with 8 bit codes
    if data.resize_default(32).is_err() {
        return Err(HidIoParseError::VecResizeFailed);
    }

    // Iterate through codes and set each bit accordingly
    for code in codes {
        let byte_pos = code / 8; // Determine which byte
        let bit_mask = 1 << (code - 8 * byte_pos); // Determine which bit
        data[byte_pos as usize] |= bit_mask;
    }
    Ok(data)
}

// ----- Implementations -----

impl<const H: usize> Default for HidIoPacketBuffer<H> {
    fn default() -> Self {
        HidIoPacketBuffer {
            ptype: HidIoPacketType::Data,
            id: HidIoCommandId::try_from(0).unwrap(),
            max_len: 64, // Default size
            data: Vec::new(),
            done: false,
        }
    }
}

impl<const H: usize> HidIoPacketBuffer<H> {
    /// Constructor for HidIoPacketBuffer
    ///
    /// # Remarks
    /// Initialize as blank
    pub fn new() -> HidIoPacketBuffer<H> {
        HidIoPacketBuffer {
            ..Default::default()
        }
    }

    /// Clear Data
    /// Sets done to false and resizes payload to 0
    pub fn clear(&mut self) {
        self.done = false;
        self.data.resize_default(0).unwrap();
    }

    /// Set Data
    pub fn set(&mut self, buf: HidIoPacketBuffer<H>) {
        self.ptype = buf.ptype;
        self.id = buf.id;
        self.max_len = buf.max_len;
        self.data = buf.data;
        self.done = buf.done;
    }

    /// Determine id_width
    fn id_width(&self) -> u8 {
        match self.id as u32 {
            0x00..=0xFFFF => 0,           // 16 bit Id
            0x01_0000..=0xFFFF_FFFF => 1, // 32 bit Id
        }
    }

    /// Determine id_width_len
    fn id_width_len(&self) -> u8 {
        match self.id_width() {
            0 => 2, // 2 bytes - 16 bit Id
            1 => 4, // 4 bytes - 32 bit Id
            _ => 0,
        }
    }

    /// Determine total header length, initial and continued packets (always 2 bytes)
    /// 1 byte for header, 1 byte for len, id_width_len for Id
    fn hdr_len(&self) -> u8 {
        2 + self.id_width_len()
    }

    /// Determine payload max length, initial and continued packets
    fn payload_len(&self) -> u32 {
        self.max_len - u32::from(self.hdr_len())
    }

    /// Serialized length of buffer
    /// Returns the currently computed serialized length of the
    /// buffer. Can change based on the struct fields.
    pub fn serialized_len(&self) -> u32 {
        // Sync packets have a serialized length of 1
        if self.ptype == HidIoPacketType::Sync {
            return 1;
        }

        let hdr_len = self.hdr_len();
        let data_len = self.data.len() as u32;
        let payload_len = self.payload_len();

        let fullpackets = (data_len / payload_len) * (payload_len + u32::from(hdr_len));
        let partialpacket = if data_len % payload_len > 0 || data_len == 0 {
            data_len % payload_len + u32::from(hdr_len)
        } else {
            0
        };

        fullpackets + partialpacket
    }

    /// Append payload data
    ///
    /// # Arguments
    /// * `new_data` - Vector of bytes
    ///
    /// # Remarks
    /// Appends payload to HidIoPacketBuffer.
    pub fn append_payload(&mut self, new_data: &[u8]) -> bool {
        // Check if buffer was already finished
        if self.done {
            warn!("HidIoPacketBuffer is already 'done'");
            return false;
        }

        self.data.extend_from_slice(new_data).is_ok()
    }

    /// Append packet stream
    /// Returns the number of bytes used.
    ///
    /// # Arguments
    /// * `packet_data` - Vector of bytes of packet data
    ///
    /// # Remarks
    /// Does packet decoding on the fly.
    /// Will set done parameter if this is the last packet.
    pub fn decode_packet(&mut self, packet_data: &[u8]) -> Result<u32, HidIoParseError> {
        // Check if buffer was already finished
        if self.done {
            warn!("HidIoPacketBuffer is already 'done'");
            return Ok(0);
        }

        let packet_data_len = packet_data.len() as u32;

        // Get packet type
        let ptype = packet_type(packet_data)?;

        // Check if this a sync packet
        if ptype == HidIoPacketType::Sync {
            self.ptype = ptype;
            self.done = true;
            return Ok(1);
        }

        // Get payload_len
        let payload_len = payload_len(packet_data)?;
        let packet_len = payload_len + 2;

        // Make sure there's actually payload_len available
        trace!(
            "decode_packet: {:?} - ptype({:?}) payload_len({:?}) packet_len({:?})",
            packet_data,
            ptype,
            payload_len,
            packet_len
        );
        if packet_data_len - 2 < payload_len {
            warn!(
                "Dropping. Not enough bytes available in packet stream. got:{}, expected:{}",
                packet_data_len - 2,
                payload_len
            );
            return Ok(packet_data_len);
        }

        // Get packet Id
        let id_num = packet_id(packet_data)?;
        let id = match HidIoCommandId::try_from(id_num) {
            Ok(id) => id,
            Err(_) => {
                error!("Failed to convert {} to HidIoCommandId", id_num);
                return Err(HidIoParseError::InvalidHidIoCommandId(id_num));
            }
        };

        // Is this a new packet?
        // More information to set, if initializing buffer
        if self.data.is_empty()
            && (ptype != HidIoPacketType::Continued && ptype != HidIoPacketType::NaContinued)
        {
            // Set packet type
            self.ptype = ptype;

            // Set packet id
            self.id = id;

        // Make sure the current buffer matches what we're expecting
        } else {
            // Check for invalid packet type
            if self.data.is_empty() && ptype == HidIoPacketType::Continued {
                warn!("Dropping. Invalid packet type when initializing buffer, HidIoPacketType::Continued");
                return Ok(packet_len);
            }
            if self.data.is_empty() && ptype == HidIoPacketType::NaContinued {
                warn!("Dropping. Invalid packet type when initializing buffer, HidIoPacketType::NaContinued");
                return Ok(packet_len);
            }

            // Check if not a continued packet, and we have a payload
            if !self.data.is_empty() {
                match ptype {
                    HidIoPacketType::Continued | HidIoPacketType::NaContinued => {}
                    _ => {
                        warn!("Dropping buffer. Invalid packet type (non-HidIoPacketType::Continued) on a already initialized buffer: {} {}", ptype, self.data.is_empty());
                        self.clear();
                        return self.decode_packet(packet_data);
                    }
                }
            }

            // Validate that we're looking at the same Id
            if self.id != id {
                warn!(
                    "Dropping. Invalid incoming id:{:?}, expected:{:?}",
                    id, self.id
                );
                return Ok(packet_len);
            }
        }

        // Payload start
        let payload_start = payload_start(packet_data)?;

        // Get id_width_len
        let id_width_len = packet_id_width(packet_data)?;

        // Check if this buffer will be completed
        self.done = !continued_packet(packet_data)?;

        // Add payload
        let slice =
            &packet_data[payload_start..payload_start + payload_len as usize - id_width_len];
        match self.data.extend_from_slice(slice) {
            Ok(_) => {}
            Err(_) => {
                return Err(HidIoParseError::PayloadAddFailed(slice.len()));
            }
        }

        // Finished
        Ok(packet_len)
    }

    /// Serialize HidIoPacketBuffer
    ///
    /// # Remarks
    /// Determine cont, width, upper_len and len fields
    /// According to this C-Struct:
    ///
    /// ```c
    /// struct HidIo_Packet {
    ///    HidIo_Packet_Type type:3;
    ///    uint8_t           cont:1;      // 0 - Only packet, 1 continued packet following
    ///    uint8_t           id_width:1;  // 0 - 16bits, 1 - 32bits
    ///    uint8_t           reserved:1;  // Reserved
    ///    uint8_t           upper_len:2; // Upper 2 bits of length field (generally unused)
    ///    uint8_t           len;         // Lower 8 bits of length field
    ///    uint8_t           data[0];     // Start of data payload (may start with Id)
    /// };
    /// ```
    pub fn serialize_buffer<'a>(&self, data: &'a mut [u8]) -> Result<&'a [u8], HidIoParseError> {
        // Check if buffer is ready to serialize
        if !self.done {
            return Err(HidIoParseError::BufferNotReady);
        }

        // --- First Packet ---

        // Keep track of the serialization buffer position
        let mut pos = 0;

        // Determine id_width
        let id_width = self.id_width();

        // Determine id_width_len
        let id_width_len = self.id_width_len();

        // Determine payload max length, initial and continued packets
        let payload_len = self.payload_len();

        // Data length
        let data_len = self.data.len() as u32;

        // Determine if a continued packet construct
        let mut cont: bool = data_len > payload_len;

        // Determine packet len
        let packet_len: u16 = if cont {
            // Full payload length
            payload_len as u16 + u16::from(id_width_len)
        } else {
            // Calculate payload length with what's left
            data_len as u16 + u16::from(id_width_len)
        };

        // Determine upper_len and len fields
        let upper_len: u8 = (packet_len >> 8) as u8;
        let len: u8 = packet_len as u8;

        // Determine ptype
        let ptype: u8 = match self.ptype {
            HidIoPacketType::Data => 0,
            HidIoPacketType::Ack => 1,
            HidIoPacketType::Nak => 2,
            HidIoPacketType::Sync => 3,
            HidIoPacketType::Continued => 4,
            HidIoPacketType::NaData => 5,
            HidIoPacketType::NaContinued => 6,
        };

        // Convert Id into bytes
        let mut id_vec: Vec<u8, 4> = Vec::new();
        for idx in 0..id_width_len {
            let id = (self.id as u32 >> (idx * 8)) as u8;
            if id_vec.push(id).is_err() {
                return Err(HidIoParseError::VecAddFailed);
            }
        }

        // Construct header byte
        let hdr_byte: u8 =
            // type - 3 bits
            (ptype << 5) |
            // cont - 1 bit
            (u8::from(cont) << 4) |
            // id_width - 1 bit
            (id_width << 3) |
            // reserved - 1 bit
            // (0 << 2) |
            // upper_len - 2 bits
            (upper_len & 0x3);

        // Header byte is always serialized
        pos = serialize_byte(data, hdr_byte, pos)?;

        // Determine if this is a sync packet (much simpler serialization)
        if self.ptype == HidIoPacketType::Sync {
            return Ok(data);
        }

        // Serialize length
        pos = serialize_byte(data, len, pos)?;

        // Serialize id
        pos = serialize_bytes(data, &id_vec[..id_width_len as usize], pos)?;

        // Serialize payload data
        // We can't just serialize directly (extra info is included), serialize each element of vector separately
        let slice = if cont {
            // Full payload length
            &self.data[0..payload_len as usize]
        } else {
            // Payload that's available
            &self.data[0..data_len as usize]
        };
        pos = serialize_bytes(data, slice, pos)?;

        // Finish serialization if no more payload left
        if !cont {
            return Ok(data);
        }

        // Determine how much payload is left
        let mut payload_left = self.data.len() as u32 - payload_len;
        let mut last_slice_index = payload_len as usize;

        // --- Additional Packets ---

        while cont {
            // Determine if continued packet construct
            cont = payload_left > payload_len;

            // Continued Packet
            let ptype = match self.ptype {
                HidIoPacketType::Ack | HidIoPacketType::Nak | HidIoPacketType::Data => {
                    HidIoPacketType::Continued as u8
                }
                HidIoPacketType::NaData => HidIoPacketType::NaContinued as u8,
                _ => {
                    warn!("Dropping. Invalid continued packet type: {:?}", self.ptype);
                    break;
                }
            };

            // Determine packet len
            let packet_len: u16 = if cont {
                // Full payload length
                payload_len as u16 + u16::from(id_width_len)
            } else {
                // Calculate payload length with what's left
                payload_left as u16 + u16::from(id_width_len)
            };

            // Determine upper_len and len fields
            let upper_len: u8 = (packet_len >> 8) as u8;
            let len: u8 = packet_len as u8;

            // Construct header byte
            let hdr_byte: u8 =
                // type - 3 bits
                (ptype << 5) |
                // cont - 1 bit
                (u8::from(cont) << 4) |
                // id_width - 1 bit
                (id_width << 3) |
                // reserved - 1 bit
                // (0 << 2) |
                // upper_len - 2 bits
                (upper_len & 0x3);

            // Serialize header
            pos = serialize_byte(data, hdr_byte, pos)?;

            // Serialize length
            pos = serialize_byte(data, len, pos)?;

            // Serialize id
            pos = serialize_bytes(data, &id_vec[..id_width_len as usize], pos)?;

            // Serialize payload data
            // We can't just serialize directly (extra info is included), serialize each element of vector separately
            let slice_end = if cont {
                // Full payload length
                last_slice_index + payload_len as usize
            } else {
                // Payload that's available
                data_len as usize
            };
            let slice = &self.data[last_slice_index..slice_end];
            pos = serialize_bytes(data, slice, pos)?;

            // Recalculate how much payload is left
            payload_left -= (slice_end - last_slice_index) as u32;
            last_slice_index += payload_len as usize;
        }

        // --- Finish serialization ---
        Ok(data)
    }
}

/// Very simple error checking function for byte serialization
/// Returns the new serialization index pointer
fn serialize_byte(data: &mut [u8], byte: u8, pos: usize) -> Result<usize, HidIoParseError> {
    // Make sure buffer is large enough
    if pos >= data.len() {
        return Err(HidIoParseError::BufferDataTooSmall(pos - 1));
    }

    data[pos] = byte;
    Ok(pos + 1)
}

/// Very simple error checking function for byte array serialization
/// Returns the new serialization index pointer
fn serialize_bytes(data: &mut [u8], bytes: &[u8], pos: usize) -> Result<usize, HidIoParseError> {
    // Make sure buffer is large enough
    if pos + bytes.len() > data.len() && !bytes.is_empty() {
        return Err(HidIoParseError::BufferDataTooSmall(pos - 1));
    }

    for (i, byte) in bytes.iter().enumerate() {
        data[pos + i] = *byte;
    }
    Ok(pos + bytes.len())
}

impl fmt::Display for HidIoPacketType {
    /// Display formatter for HidIoPacketType
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let ptype_name = match *self {
            HidIoPacketType::Data => "HidIoPacketBuffer::Data",
            HidIoPacketType::Ack => "HidIoPacketBuffer::Ack",
            HidIoPacketType::Nak => "HidIoPacketBuffer::Nak",
            HidIoPacketType::Sync => "HidIoPacketBuffer::Sync",
            HidIoPacketType::Continued => "HidIoPacketBuffer::Continued",
            HidIoPacketType::NaData => "HidIoPacketBuffer::NaData",
            HidIoPacketType::NaContinued => "HidIoPacketBuffer::NaContinued",
        };
        write!(f, "{ptype_name}")
    }
}

impl<const H: usize> fmt::Display for HidIoPacketBuffer<H> {
    /// Display formatter for HidIoPacketBuffer
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "\n{{\n    ptype: {}\n    id: {:?}\n    max_len: {}\n    done: {}\n    data: {:#?}\n}}",
            self.ptype, self.id, self.max_len, self.done, self.data,
        )
    }
}