gr::digital::header_buffer
gnuradio/digital/header_buffer.h
size_t size_t gr::digital::header_buffer::d_offset d_offset gr::digital::header_buffer::d_offset
uint8_t * uint8_t* gr::digital::header_buffer::d_buffer d_buffer gr::digital::header_buffer::d_buffer
std::vector< bool > std::vector<bool> gr::digital::header_buffer::d_input d_input gr::digital::header_buffer::d_input
gr::digital::header_buffer::header_buffer
(uint8_t *buffer=NULL)
header_buffer
gr::digital::header_buffer::header_buffer
uint8_t * buffer NULL

Create a header buffer object with a pre-allocated buffer, `buffer`, to hold the formatted header data.

If `buffer` is set to NULL, then this object is in receive mode meant to receive bits from an incoming data stream and provide the ability to extract fields. In this mode, calls to add_field are invalid and will be nops.

gr::digital::header_buffer::~header_buffer
()
~header_buffer
gr::digital::header_buffer::~header_buffer

Class destructor.

void void gr::digital::header_buffer::clear () clear gr::digital::header_buffer::clear

Clears the header.

In transmit mode, this resets the current offset so new add_field functions start adding data to the start of the buffer.

In receive mode, this clears the buffer that we have inserted bits in to.

size_t size_t gr::digital::header_buffer::length () const length gr::digital::header_buffer::length

In transmit mode, this returns the length of the data in the buffer (not the allocated buffer length).

In receiving mode, this returns the current length in bits of the received header.

const uint8_t * const uint8_t * gr::digital::header_buffer::header () const header gr::digital::header_buffer::header

Returns a constant pointer to the buffer.

void void gr::digital::header_buffer::add_field8 (uint8_t data, int len=8, bool bs=false) add_field8 gr::digital::header_buffer::add_field8 uint8_t data int len 8 bool bs false

Add an 8-bit field to the header.

data

The 8-bit data item.

len

Length (in bits) of `data`.

bs

Set to 'true' to byte swap the data.

void void gr::digital::header_buffer::add_field16 (uint16_t data, int len=16, bool bs=false) add_field16 gr::digital::header_buffer::add_field16 uint16_t data int len 16 bool bs false

Add an 16-bit field to the header.

data

The 16-bit data item.

len

Length (in bits) of `data`.

bs

Set to 'true' to byte swap the data.

void void gr::digital::header_buffer::add_field32 (uint32_t data, int len=32, bool bs=false) add_field32 gr::digital::header_buffer::add_field32 uint32_t data int len 32 bool bs false

Add an 32-bit field to the header.

data

The 32-bit data item.

len

Length (in bits) of `data`.

bs

Set to 'true' to byte swap the data.

void void gr::digital::header_buffer::add_field64 (uint64_t data, int len=64, bool bs=false) add_field64 gr::digital::header_buffer::add_field64 uint64_t data int len 64 bool bs false

Add an 64-bit field to the header.

data

The 64-bit data item.

len

Length (in bits) of `data`.

bs

Set to 'true' to byte swap the data.

void void gr::digital::header_buffer::insert_bit (int bit) insert_bit gr::digital::header_buffer::insert_bit int bit

Insert a new bit on the back of the input buffer. This function is used in receive mode to add new bits as they are received for later use of the extract_field functions.

bit

New bit to add.

class T
T T gr::digital::header_buffer::extract_field (int pos, int len=8 *sizeof(T), bool bs=false, bool lsb_first=false) extract_field gr::digital::header_buffer::extract_field int pos int len 8 *sizeof(T) bool bs false bool lsb_first false

Returns a field in the packet header.

pos

Bit position of the start of the field.

len

The number of bits in the field.

bs

Set to 'true' to byte swap the data.

lsb_first

Set to 'true' to read field encoded as least significant bit first

extract_field16
extract_field32
extract_field64
extract_field8
uint8_t uint8_t gr::digital::header_buffer::extract_field8 (int pos, int len=8, bool bs=false, bool lsb_first=false) extract_field8 gr::digital::header_buffer::extract_field8 int pos int len 8 bool bs false bool lsb_first false

Returns up to an 8-bit field in the packet header.

pos

Bit position of the start of the field.

len

The number of bits in the field.

bs

Set to 'true' to byte swap the data.

lsb_first

Set to 'true' to read field encoded as least significant bit first

extract_field
uint16_t uint16_t gr::digital::header_buffer::extract_field16 (int pos, int len=16, bool bs=false, bool lsb_first=false) extract_field16 gr::digital::header_buffer::extract_field16 int pos int len 16 bool bs false bool lsb_first false

Returns up to a 16-bit field in the packet header.

pos

Bit position of the start of the field.

len

The number of bits in the field.

bs

Set to 'true' to byte swap the data.

lsb_first

Set to 'true' to read field encoded as least significant bit first

extract_field
uint32_t uint32_t gr::digital::header_buffer::extract_field32 (int pos, int len=32, bool bs=false, bool lsb_first=false) extract_field32 gr::digital::header_buffer::extract_field32 int pos int len 32 bool bs false bool lsb_first false

Returns up to a 32-bit field in the packet header.

pos

Bit position of the start of the field.

len

The number of bits in the field.

bs

Set to 'true' to byte swap the data.

lsb_first

Set to 'true' to read field encoded as least significant bit first

extract_field
uint64_t uint64_t gr::digital::header_buffer::extract_field64 (int pos, int len=64, bool bs=false, bool lsb_first=false) extract_field64 gr::digital::header_buffer::extract_field64 int pos int len 64 bool bs false bool lsb_first false

Returns up to a 64-bit field in the packet header.

pos

Bit position of the start of the field.

len

The number of bits in the field.

bs

Set to 'true' to byte swap the data.

lsb_first

Set to 'true' to read field encoded as least significant bit first

extract_field

Helper class for handling payload headers.

This class is used by the header format blocks (e.g., digital::header_format_default) to make it easier to deal with payload headers. This class functions in two different ways depending on if it is used in a transmitter or receiver. When used in a transmitter, this class helps us build headers out of the fields of the protocol. When used in a receiver, this class helps us parse the received bits into the protocol's fields.

This page describes how to work with the different modes, transmit or receive. The class is instructed as to which mode it is in by how the constructor is called. If the constructor is passed a valid array (non NULL), then it is in transmit mode and will pack this buffer with the header fields. If that buffer is NULL, the object is in receive mode.

# Transmit Mode

When passed a valid buffer in the constructor, this object is in transmit mode. We can then use the add_field[N] functions to add new fields to this header. The buffer MUST be large enough to hold the full header. As this class is meant to work mostly with the digital::header_format_default and child classes, the header length can be read from digital::header_format_default::header_nbytes().

Each field is a specific length of 8, 16, 32, or 64 bits that are to be transmitted in network byte order. We can adjust the direction of the bytes by setting the byte-swap flag, `bs`, to true or false.

The length argument (`len`) for all add_field[N] calls is the number of bytes actually accounted for in the data structure. Often, we would use the full size of the field, which is sizeof(dtype), and the add_field[N] call defaults to len=N. Occasionally, we may need to use fewer bytes than actually represented by the data type. An example would be the access code used in the header_format_default, which is a uint64_t type but may have fewer bytes used in the actual access code.

The function that calls this class is expected to handle the memory handling of the buffer both allocating and deallocating.

As simple example of using this class in transmit mode:

volk::vector<uint8_t> buffer(header_nbytes()); header_buffer hdr(buffer); hdr.add_field64(sync_word, sync_word_len); hdr.add_field16(payload_length); hdr.add_field8(header_flags); hdr.add_field8(header_options); // Do something with the header

In this example, the header contains four fields:

|0 15|16 23|24 31| | sync word | | | | length | flags | options |

The sync word can be up to 64-bits, but the add_field64 is also passed the number of actual bytes in the sync word and so could be fewer.

# Receive Mode

In receive mode, we build up the header as bits are received by inserting them with insert_bit. We can find out how long the current header is, in bits, using the call to length(). If the header is of the appropriate length, we can then start extracting the fields from it. When we are done with the current header, call clear() to reset the internal buffer to empty, which will mean that length() returns 0.

The header fields are extracted using the extract_field[N] functions. Like the add_field[N] functions, we specify the size (in bits) of the field we are extracting. We pass this function the bit-position of the expected field in the received header buffer. The extract_field[N] assumes that the number of bits for the field is N, but we can tell the function to use fewer bits if we want. Setting the length parameter of these functions greater than N is illegal, and it will throw an error.

For example, given a header of | length | seq. num. | where the length is 16 bits and the sequence number is 32 bits, we would use:

uint16_t len = d_hdr_reg.extract_field16(0); uint32_t seq = d_hdr_reg.extract_field32(16);

The extract_field functions are specific to data types of the field and the number of bits for each field is inferred by the data type. So extract_field16 assumes we want all 16 bits in the field represented.

Some headers have fields that are not standard sizes of integers, like a 1 bit, 4 bit, or even 12 bit fields. We can ask for fewer bits for each field. say:

|0 15|16 19|20 31| | len | flags | options |

We would use the following extraction functions:

uint16_t len = d_hdr_reg.extract_field16(0); uint8_t flags = d_hdr_reg.extract_field8(16, 4); uint16_t opts = d_hdr_reg.extract_field16(20, 12);

header_format_default

header_format_counter

header_format_crc

- gr::digital::header_buffer
  add_field16
- gr::digital::header_buffer
  add_field32
- gr::digital::header_buffer
  add_field64
- gr::digital::header_buffer
  add_field8
- gr::digital::header_buffer
  clear
- gr::digital::header_buffer
  d_buffer
- gr::digital::header_buffer
  d_input
- gr::digital::header_buffer
  d_offset
- gr::digital::header_buffer
  extract_field
- gr::digital::header_buffer
  extract_field16
- gr::digital::header_buffer
  extract_field32
- gr::digital::header_buffer
  extract_field64
- gr::digital::header_buffer
  extract_field8
- gr::digital::header_buffer
  header
- gr::digital::header_buffer
  header_buffer
- gr::digital::header_buffer
  insert_bit
- gr::digital::header_buffer
  length
- gr::digital::header_buffer
  ~header_buffer