HDLCStream Class Reference

High-Level Data Link Control (HDLC) is a bit-oriented code-transparent synchronous data link layer protocol for reliable, framed, and error-checked communication. More...

#include <HDLCStream.h>

Inheritance diagram for HDLCStream:

Public Member Functions
	HDLCStream (Print &stream, size_t maxFrameSize)
	Construct a new HDLCStream object using a Print for output only.
	HDLCStream (Stream &stream, size_t maxFrameSize)
	Construct a new HDLCStream object using a Stream for input and output.
int	available () override
	Get the number of bytes available to read from the frame buffer.
virtual int	availableForWrite ()
void	flush () override
	Flush the output buffer of the underlying stream.
	operator bool ()
int	peek () override
	Not supported.
int	read () override
	Not supported.
size_t	readBytes (uint8_t *buffer, size_t length) override
	Read a full frame from the stream into a buffer.
size_t	write (const uint8_t *data, size_t len) override
	Write multiple bytes to the stream.
size_t	write (uint8_t b) override
	Not supported.

Protected Types
enum	RxState { IDLE , RECEIVING , ESCAPED }

Protected Member Functions
uint16_t	_crc16 (uint8_t data, uint16_t crc)
	Calculate CRC-CCITT (16-bit)
void	_processInput ()
	Process incoming bytes, detect frames, validate CRC and prepare data for reading.
void	_writeEscaped (uint8_t b)
	Write a byte with proper HDLC byte stuffing if needed.
size_t	writeFrame (const uint8_t *data, size_t len)
	Write a complete HDLC frame with proper framing and CRC.

Protected Attributes
size_t	_frameLen = 0
bool	_frameReady = false
const size_t	_maxFrameSize
Vector< uint8_t >	_rxBuffer
size_t	_rxLen = 0
size_t	_rxPos = 0
enum audio_tools::HDLCStream::RxState	_rxState = IDLE
int	_timeout = 10
Print *	p_print = nullptr
Stream *	p_stream = nullptr
SingleBuffer< uint8_t >	rx_frame_buffer
SingleBuffer< uint8_t >	tx_frame_buffer

Static Protected Attributes
static constexpr uint8_t	HDLC_ESC = 0x7D
static constexpr uint8_t	HDLC_ESC_XOR = 0x20
static constexpr uint8_t	HDLC_FLAG = 0x7E

Detailed Description

High-Level Data Link Control (HDLC) is a bit-oriented code-transparent synchronous data link layer protocol for reliable, framed, and error-checked communication.

This class implements HDLC framing with:

• Frame delimiter (0x7E) for marking frame boundaries
• Byte stuffing to escape special characters in the data
• 16-bit CRC-CCITT for error detection
• Transparent Stream interface for easy integration

Author

Phil Schatzmann

Constructor & Destructor Documentation

HDLCStream() [1/2]

HDLCStream ( Stream &  stream, size_t  maxFrameSize  )

inline

Construct a new HDLCStream object using a Stream for input and output.

Parameters

stream	The underlying Stream for both reading and writing
maxFrameSize	Maximum size of a single HDLC frame

HDLCStream() [2/2]

HDLCStream ( Print &  stream, size_t  maxFrameSize  )

inline

Construct a new HDLCStream object using a Print for output only.

Parameters

stream	The underlying Print for writing
maxFrameSize	Maximum size of a single HDLC frame

Member Function Documentation

_crc16()

uint16_t _crc16 ( uint8_t  data, uint16_t  crc  )

inlineprotected

Calculate CRC-CCITT (16-bit)

Parameters

data	Byte to include in CRC calculation
crc	Current CRC value

Returns

uint16_t Updated CRC value

_writeEscaped()

void _writeEscaped ( uint8_t  b )

inlineprotected

Write a byte with proper HDLC byte stuffing if needed.

Parameters

b	Byte to write

available()

int available ( )

inlineoverridevirtual

Get the number of bytes available to read from the frame buffer.

Returns

int Number of bytes available

Reimplemented from Stream.

availableForWrite()

virtual int availableForWrite ( )

inlinevirtualinherited

Reimplemented in RTSPOutput, UDPStream, A2DPStream, AudioFFTBase, I2SCodecStream, Equalizer3Bands, Equalizer3BandsPerChannel, AbstractURLStream, URLStreamESP32, I2SStream, OutputMixer< T >, MeasuringStream, ProgressStream, FrequencyDetectorAutoCorrelation, FrequencyDetectorZeroCrossing, and VolumeStream.

flush()

void flush ( )

inlineoverridevirtual

Flush the output buffer of the underlying stream.

Reimplemented from Print.

peek()

int peek ( )

inlineoverride

Not supported.

Returns

-1

read()

int read ( )

inlineoverride

Not supported.

Returns

-1

readBytes()

size_t readBytes ( uint8_t *  buffer, size_t  length  )

inlineoverridevirtual

Read a full frame from the stream into a buffer.

Parameters

buffer	Destination buffer to hold the data
length	Maximum number of bytes to read

Returns

size_t Actual number of bytes read

Reimplemented from Stream.

write() [1/2]

size_t write ( const uint8_t *  data, size_t  len  )

inlineoverridevirtual

Write multiple bytes to the stream.

Parameters

data	Pointer to the data buffer
len	Number of bytes to write

Returns

size_t Number of bytes written

Reimplemented from Print.

write() [2/2]

size_t write ( uint8_t  b )

inlineoverride

Not supported.

Parameters

b	The byte to write

Returns

0

writeFrame()

size_t writeFrame ( const uint8_t *  data, size_t  len  )

inlineprotected

Write a complete HDLC frame with proper framing and CRC.

Parameters

data	Data to be framed
len	Length of data

Returns

size_t Number of bytes in the original data

---

The documentation for this class was generated from the following file:

• src/AudioTools/Communication/HDLCStream.h