gr::digital::header_payload_demux Class Reference

Header/Payload demuxer (HPD). More...

#include <gnuradio/digital/header_payload_demux.h>

Public Types
typedef boost::shared_ptr< header_payload_demux >	sptr
Public Types inherited from gr::block
enum	{ WORK_CALLED_PRODUCE = -2, WORK_DONE = -1 }
	Magic return values from general_work. More...
enum	tag_propagation_policy_t { TPP_DONT = 0, TPP_ALL_TO_ALL = 1, TPP_ONE_TO_ONE = 2, TPP_CUSTOM = 3 }
	enum to represent different tag propagation policies. More...

Static Public Member Functions
static sptr	make (const int header_len, const int items_per_symbol=1, const int guard_interval=0, const std::string &length_tag_key="frame_len", const std::string &trigger_tag_key="", const bool output_symbols=false, const size_t itemsize=sizeof(gr_complex), const std::string &timing_tag_key="", const double samp_rate=1.0, const std::vector< std::string > &special_tags=std::vector< std::string >(), const size_t header_padding=0)

Additional Inherited Members
Public Member Functions inherited from gr::block
virtual	~block ()
unsigned	history () const
void	set_history (unsigned history)
void	declare_sample_delay (int which, unsigned delay)
void	declare_sample_delay (unsigned delay)
unsigned	sample_delay (int which) const
bool	fixed_rate () const
	Return true if this block has a fixed input to output rate. More...
virtual void	forecast (int noutput_items, gr_vector_int &ninput_items_required)
	Estimate input requirements given output request. More...
virtual int	general_work (int noutput_items, gr_vector_int &ninput_items, gr_vector_const_void_star &input_items, gr_vector_void_star &output_items)
	compute output items from input items More...
virtual bool	start ()
	Called to enable drivers, etc for i/o devices. More...
virtual bool	stop ()
	Called to disable drivers, etc for i/o devices. More...
void	set_output_multiple (int multiple)
	Constrain the noutput_items argument passed to forecast and general_work. More...
int	output_multiple () const
bool	output_multiple_set () const
void	set_alignment (int multiple)
	Constrains buffers to work on a set item alignment (for SIMD) More...
int	alignment () const
void	set_unaligned (int na)
int	unaligned () const
void	set_is_unaligned (bool u)
bool	is_unaligned () const
void	consume (int which_input, int how_many_items)
	Tell the scheduler how_many_items of input stream which_input were consumed. More...
void	consume_each (int how_many_items)
	Tell the scheduler how_many_items were consumed on each input stream. More...
void	produce (int which_output, int how_many_items)
	Tell the scheduler how_many_items were produced on output stream which_output. More...
void	set_relative_rate (double relative_rate)
	Set the approximate output rate / input rate. More...
void	set_inverse_relative_rate (double inverse_relative_rate)
	Set the approximate output rate / input rate using its reciprocal. More...
void	set_relative_rate (uint64_t interpolation, uint64_t decimation)
	Set the approximate output rate / input rate as an integer ratio. More...
double	relative_rate () const
	return the approximate output rate / input rate More...
uint64_t	relative_rate_i () const
	return the numerator, or interpolation rate, of the approximate output rate / input rate More...
uint64_t	relative_rate_d () const
	return the denominator, or decimation rate, of the approximate output rate / input rate More...
mpq_class &	mp_relative_rate ()
	return a reference to the multiple precision rational represntation of the approximate output rate / input rate More...
virtual int	fixed_rate_ninput_to_noutput (int ninput)
	Given ninput samples, return number of output samples that will be produced. N.B. this is only defined if fixed_rate returns true. Generally speaking, you don't need to override this. More...
virtual int	fixed_rate_noutput_to_ninput (int noutput)
	Given noutput samples, return number of input samples required to produce noutput. N.B. this is only defined if fixed_rate returns true. Generally speaking, you don't need to override this. More...
uint64_t	nitems_read (unsigned int which_input)
	Return the number of items read on input stream which_input. More...
uint64_t	nitems_written (unsigned int which_output)
	Return the number of items written on output stream which_output. More...
tag_propagation_policy_t	tag_propagation_policy ()
	Asks for the policy used by the scheduler to moved tags downstream. More...
void	set_tag_propagation_policy (tag_propagation_policy_t p)
	Set the policy by the scheduler to determine how tags are moved downstream. More...
int	min_noutput_items () const
	Return the minimum number of output items this block can produce during a call to work. More...
void	set_min_noutput_items (int m)
	Set the minimum number of output items this block can produce during a call to work. More...
int	max_noutput_items ()
	Return the maximum number of output items this block will handle during a call to work. More...
void	set_max_noutput_items (int m)
	Set the maximum number of output items this block will handle during a call to work. More...
void	unset_max_noutput_items ()
	Clear the switch for using the max_noutput_items value of this block. More...
bool	is_set_max_noutput_items ()
	Ask the block if the flag is or is not set to use the internal value of max_noutput_items during a call to work. More...
void	expand_minmax_buffer (int port)
long	max_output_buffer (size_t i)
	Returns max buffer size on output port i. More...
void	set_max_output_buffer (long max_output_buffer)
	Request limit on max buffer size on all output ports. More...
void	set_max_output_buffer (int port, long max_output_buffer)
	Request limit on max buffer size on output port port. More...
long	min_output_buffer (size_t i)
	Returns min buffer size on output port i. More...
void	set_min_output_buffer (long min_output_buffer)
	Request limit on the minimum buffer size on all output ports. More...
void	set_min_output_buffer (int port, long min_output_buffer)
	Request limit on min buffer size on output port port. More...
float	pc_noutput_items ()
	Gets instantaneous noutput_items performance counter. More...
float	pc_noutput_items_avg ()
	Gets average noutput_items performance counter. More...
float	pc_noutput_items_var ()
	Gets variance of noutput_items performance counter. More...
float	pc_nproduced ()
	Gets instantaneous num items produced performance counter. More...
float	pc_nproduced_avg ()
	Gets average num items produced performance counter. More...
float	pc_nproduced_var ()
	Gets variance of num items produced performance counter. More...
float	pc_input_buffers_full (int which)
	Gets instantaneous fullness of which input buffer. More...
float	pc_input_buffers_full_avg (int which)
	Gets average fullness of which input buffer. More...
float	pc_input_buffers_full_var (int which)
	Gets variance of fullness of which input buffer. More...
std::vector< float >	pc_input_buffers_full ()
	Gets instantaneous fullness of all input buffers. More...
std::vector< float >	pc_input_buffers_full_avg ()
	Gets average fullness of all input buffers. More...
std::vector< float >	pc_input_buffers_full_var ()
	Gets variance of fullness of all input buffers. More...
float	pc_output_buffers_full (int which)
	Gets instantaneous fullness of which output buffer. More...
float	pc_output_buffers_full_avg (int which)
	Gets average fullness of which output buffer. More...
float	pc_output_buffers_full_var (int which)
	Gets variance of fullness of which output buffer. More...
std::vector< float >	pc_output_buffers_full ()
	Gets instantaneous fullness of all output buffers. More...
std::vector< float >	pc_output_buffers_full_avg ()
	Gets average fullness of all output buffers. More...
std::vector< float >	pc_output_buffers_full_var ()
	Gets variance of fullness of all output buffers. More...
float	pc_work_time ()
	Gets instantaneous clock cycles spent in work. More...
float	pc_work_time_avg ()
	Gets average clock cycles spent in work. More...
float	pc_work_time_var ()
	Gets average clock cycles spent in work. More...
float	pc_work_time_total ()
	Gets total clock cycles spent in work. More...
float	pc_throughput_avg ()
	Gets average throughput. More...
void	reset_perf_counters ()
	Resets the performance counters. More...
void	setup_pc_rpc ()
	Sets up export of perf. counters to ControlPort. Only called by the scheduler. More...
bool	is_pc_rpc_set ()
	Checks if this block is already exporting perf. counters to ControlPort. More...
void	no_pc_rpc ()
	If the block calls this in its constructor, it's perf. counters will not be exported. More...
void	set_processor_affinity (const std::vector< int > &mask)
	Set the thread's affinity to processor core n. More...
void	unset_processor_affinity ()
	Remove processor affinity to a specific core. More...
std::vector< int >	processor_affinity ()
	Get the current processor affinity. More...
int	active_thread_priority ()
	Get the current thread priority in use. More...
int	thread_priority ()
	Get the current thread priority stored. More...
int	set_thread_priority (int priority)
	Set the current thread priority. More...
bool	update_rate () const
void	system_handler (pmt::pmt_t msg)
	the system message handler More...
void	set_log_level (std::string level)
	Set the logger's output level. More...
std::string	log_level ()
	Get the logger's output level. More...
bool	finished ()
	returns true when execution has completed due to a message connection More...
block_detail_sptr	detail () const
void	set_detail (block_detail_sptr detail)
void	notify_msg_neighbors ()
	Tell msg neighbors we are finished. More...
void	clear_finished ()
	Make sure we don't think we are finished. More...
std::string	identifier () const
Public Member Functions inherited from gr::basic_block
pmt::pmt_t	message_subscribers (pmt::pmt_t port)
virtual	~basic_block ()
long	unique_id () const
long	symbolic_id () const
std::string	name () const
std::string	symbol_name () const
std::string	identifier () const
gr::io_signature::sptr	input_signature () const
gr::io_signature::sptr	output_signature () const
basic_block_sptr	to_basic_block ()
bool	alias_set () const
std::string	alias () const
pmt::pmt_t	alias_pmt () const
void	set_block_alias (std::string name)
void	message_port_register_in (pmt::pmt_t port_id)
void	message_port_register_out (pmt::pmt_t port_id)
void	message_port_pub (pmt::pmt_t port_id, pmt::pmt_t msg)
void	message_port_sub (pmt::pmt_t port_id, pmt::pmt_t target)
void	message_port_unsub (pmt::pmt_t port_id, pmt::pmt_t target)
virtual bool	message_port_is_hier (pmt::pmt_t port_id)
virtual bool	message_port_is_hier_in (pmt::pmt_t port_id)
virtual bool	message_port_is_hier_out (pmt::pmt_t port_id)
pmt::pmt_t	message_ports_in ()
	Get input message port names. More...
pmt::pmt_t	message_ports_out ()
	Get output message port names. More...
void	_post (pmt::pmt_t which_port, pmt::pmt_t msg)
bool	empty_p (pmt::pmt_t which_port)
	is the queue empty? More...
bool	empty_p ()
bool	empty_handled_p (pmt::pmt_t which_port)
	are all msg ports with handlers empty? More...
bool	empty_handled_p ()
size_t	nmsgs (pmt::pmt_t which_port)
	How many messages in the queue? More...
void	insert_tail (pmt::pmt_t which_port, pmt::pmt_t msg)
pmt::pmt_t	delete_head_nowait (pmt::pmt_t which_port)
msg_queue_t::iterator	get_iterator (pmt::pmt_t which_port)
void	erase_msg (pmt::pmt_t which_port, msg_queue_t::iterator it)
virtual bool	has_msg_port (pmt::pmt_t which_port)
const msg_queue_map_t &	get_msg_map (void) const
virtual void	setup_rpc ()
	Set up the RPC registered variables. More...
bool	is_rpc_set ()
	Ask if this block has been registered to the RPC. More...
void	rpc_set ()
	When the block is registered with the RPC, set this. More...
virtual bool	check_topology (int ninputs, int noutputs)
	Confirm that ninputs and noutputs is an acceptable combination. More...
template<typename T >
void	set_msg_handler (pmt::pmt_t which_port, T msg_handler)
	Set the callback that is fired when messages are available. More...
Public Member Functions inherited from gr::msg_accepter
	msg_accepter ()
	~msg_accepter ()
void	post (pmt::pmt_t which_port, pmt::pmt_t msg)
	send msg to msg_accepter on port which_port More...
Public Member Functions inherited from gr::messages::msg_accepter
	msg_accepter ()
Protected Types inherited from gr::basic_block
enum	vcolor { WHITE, GREY, BLACK }
Protected Member Functions inherited from gr::block
	block (void)
	block (const std::string &name, gr::io_signature::sptr input_signature, gr::io_signature::sptr output_signature)
void	set_fixed_rate (bool fixed_rate)
void	add_item_tag (unsigned int which_output, uint64_t abs_offset, const pmt::pmt_t &key, const pmt::pmt_t &value, const pmt::pmt_t &srcid=pmt::PMT_F)
	Adds a new tag onto the given output buffer. More...
void	add_item_tag (unsigned int which_output, const tag_t &tag)
	Adds a new tag onto the given output buffer. More...
void	remove_item_tag (unsigned int which_input, uint64_t abs_offset, const pmt::pmt_t &key, const pmt::pmt_t &value, const pmt::pmt_t &srcid=pmt::PMT_F)
	DEPRECATED. Will be removed in 3.8. More...
void	remove_item_tag (unsigned int which_input, const tag_t &tag)
	DEPRECATED. Will be removed in 3.8. More...
void	get_tags_in_range (std::vector< tag_t > &v, unsigned int which_input, uint64_t abs_start, uint64_t abs_end)
	Given a [start,end), returns a vector of all tags in the range. More...
void	get_tags_in_range (std::vector< tag_t > &v, unsigned int which_input, uint64_t abs_start, uint64_t abs_end, const pmt::pmt_t &key)
	Given a [start,end), returns a vector of all tags in the range with a given key. More...
void	get_tags_in_window (std::vector< tag_t > &v, unsigned int which_input, uint64_t rel_start, uint64_t rel_end)
	Gets all tags within the relative window of the current call to work. More...
void	get_tags_in_window (std::vector< tag_t > &v, unsigned int which_input, uint64_t rel_start, uint64_t rel_end, const pmt::pmt_t &key)
	Operates like gr::block::get_tags_in_window with the ability to only return tags with the specified key. More...
void	enable_update_rate (bool en)
Protected Member Functions inherited from gr::basic_block
	basic_block (void)
	basic_block (const std::string &name, gr::io_signature::sptr input_signature, gr::io_signature::sptr output_signature)
	Protected constructor prevents instantiation by non-derived classes. More...
void	set_input_signature (gr::io_signature::sptr iosig)
	may only be called during constructor More...
void	set_output_signature (gr::io_signature::sptr iosig)
	may only be called during constructor More...
void	set_color (vcolor color)
	Allow the flowgraph to set for sorting and partitioning. More...
vcolor	color () const
virtual bool	has_msg_handler (pmt::pmt_t which_port)
	Tests if there is a handler attached to port which_port. More...
virtual void	dispatch_msg (pmt::pmt_t which_port, pmt::pmt_t msg)
Protected Attributes inherited from gr::block
std::vector< long >	d_max_output_buffer
std::vector< long >	d_min_output_buffer
gr::thread::mutex	d_setlock
gr::logger_ptr	d_logger
gr::logger_ptr	d_debug_logger
const pmt::pmt_t	d_pmt_done
const pmt::pmt_t	d_system_port
Protected Attributes inherited from gr::basic_block
std::string	d_name
gr::io_signature::sptr	d_input_signature
gr::io_signature::sptr	d_output_signature
long	d_unique_id
long	d_symbolic_id
std::string	d_symbol_name
std::string	d_symbol_alias
vcolor	d_color
bool	d_rpc_set
msg_queue_map_t	msg_queue
std::vector< rpcbasic_sptr >	d_rpc_vars
pmt::pmt_t	d_message_subscribers

Detailed Description

Header/Payload demuxer (HPD).

This block is designed to demultiplex packets from a bursty transmission. The typical application for this block is the case when you are receiving packets with yet-to-determine length. This block will pass the header section to other blocks for demodulation. Using the information from the demodulated header, it will then output the payload. The beginning of the header needs to be identified by a trigger signal (see below).

Theory of Operation

Input 0 takes a continuous transmission of samples (items). Input 1 is an optional input for the trigger signal (mark beginning of packets). In this case, a non-zero value on input 1 identifies the beginning of a packet. Otherwise, a tag with the key specified in trigger_tag_key is used as a trigger (its value is irrelevant).

Until a trigger signal is detected, all samples are dropped onto the floor. Once a trigger is detected, a total of header_len items are copied to output 0. The block then stalls until it receives a message on the message port header_data. The message must be a PMT dictionary; all key/value pairs are copied as tags to the first item of the payload (which is assumed to be the first item after the header). The value corresponding to the key specified in length_tag_key is read and taken as the payload length. The payload, together with the header data as tags, is then copied to output 1.

If the header demodulation fails, the header must send a PMT with value pmt::PMT_F. The state gets reset and the header is ignored.

Symbols, Items and Item Sizes

To generically and transparently handle different kinds of modulations, including OFDM, this block distinguises between symbols and items.

Items are what are consumed at the input. Anything that uses complex samples will therefore use an itemsize of sizeof(gr_complex). Symbols are a way of grouping items. In OFDM, we usually don't care about individual samples, but we do care about full OFDM symbols, so we set items_per_symbol to the IFFT / FFT length of the OFDM modulator / demodulator. For single-carrier modulations, this value can be set to the number of samples per symbol, to handle data in number of symbols, or to 1 to handle data in number of samples. If specified, guard_interval items are discarded before every symbol. This is useful for demuxing bursts of OFDM signals.

On the output, we can deal with symbols directly by setting output_symbols to true. In that case, the output item size is the symbol size.

Example: OFDM with 48 sub-carriers, using a length-64 IFFT on the modulator, and a cyclic-prefix length of 16 samples. In this case, itemsize is sizeof(gr_complex), because we're receiving complex samples. One OFDM symbol has 64 samples, hence items_per_symbol is set to 64, and guard_interval to 16. The header length is specified in number of OFDM symbols. Because we want to deal with full OFDM symbols, we set output_symbols to true.

Example: PSK-modulated signals, with 4 samples per symbol. Again, itemsize is sizeof(gr_complex) because we're still dealing with complex samples. items_per_symbol is 4, because one item is one sample. guard_interval must be set to 0. The header length is given in number of PSK symbols.

Handling timing uncertainty on the trigger

By default, the assumption is made that the trigger arrives on exactly the sample that the header starts. These triggers typically come from timing synchronization algorithms which may be suboptimal, and have a known timing uncertainty (e.g., we know the trigger might be a sample too early or too late).

The demuxer has an option for this case, the header_padding. If this value is non-zero, it specifies the number of items that are prepended and appended to the header before copying it to the header output.

Example: Say our synchronization algorithm can be off by up to two samples, and the header length is 20 samples. So we set header_len to 20, and header_padding to 2. Now assume a trigger arrives on sample index 100. We copy a total of 24 samples to the header port, starting at sample index 98.

The payload is not padded. Let's say the header demod reports a payload length of 100. In the previous examples, we would copy 100 samples to the payload port, starting at sample index 120 (this means the padded samples appended to the header are copied to both ports!). However, the header demodulator has the option to specify a payload offset, which cannot exceed the padding value. To do this, include a key payload_offset in the message sent back to the HPD. A negative value means the payload starts earlier than otherwise. (If you wanted to always pad the payload, you could set payload_offset to -header_padding and increase the reported length of the payload).

Because the padding is specified in number of items, and not symbols, this value can only be multiples of the number of items per symbol if either output_symbols is true, or a guard interval is specified (or both). Note that in practice, it is rare that both a guard interval is specified and a padding value is required. The difference between the padding value and a guard interval is that a guard interval is part of the signal, and comes with every symbol, whereas the header padding is added to only the header, and is not by design.

Tag Handling

Any tags on the input stream are copied to the corresponding output if they're on an item that is propagated. Note that a tag on the header items is copied to the header stream; that means the header-parsing block must handle these tags if they should go on the payload. A special case are tags on items that make up the guard interval. These are copied to the first item of the following symbol. If a tag is situated very close to the end of the payload, it might be unclear if it belongs to this packet or the following. In this case, it is possible that the tag might be propagated twice.

Tags outside of packets are generally discarded. If there are tags that carry important information that must not be list, there are two additional mechanisms to preserve the tags:

• Timing tags might be relevant to know when a packet was received. By specifying the name of a timestamp tag and the sample rate at this block, it keeps track of the time and will add the time to the first item of every packet. The name of the timestamp tag is usually 'rx_time' (see, e.g., gr::uhd::usrp_source::make()). The time value must be specified in the UHD time format.
• Other tags are simply stored and updated. As an example, the user might want to know the rx frequency, which UHD stores in the rx_freq tag. In this case, add the tag name 'rx_freq' to the list of special_tags. This block will then always save the most current value of 'rx_freq' and add it to the beginning of every packet.

Member Typedef Documentation

sptr

typedef boost::shared_ptr<header_payload_demux> gr::digital::header_payload_demux::sptr

Member Function Documentation

make()

static sptr gr::digital::header_payload_demux::make ( const int  header_len, const int  items_per_symbol = 1, const int  guard_interval = 0, const std::string &  length_tag_key = "frame_len", const std::string &  trigger_tag_key = "", const bool  output_symbols = false, const size_t  itemsize = sizeof(gr_complex), const std::string &  timing_tag_key = "", const double  samp_rate = 1.0, const std::vector< std::string > &  special_tags = std::vector< std::string >(), const size_t  header_padding = 0  )

static

Parameters

header_len	Number of symbols per header
items_per_symbol	Number of items per symbol
guard_interval	Number of items between two consecutive symbols
length_tag_key	Key of the frame length tag
trigger_tag_key	Key of the trigger tag
output_symbols	Output symbols (true) or items (false)?
itemsize	Item size (bytes per item)
timing_tag_key	The name of the tag with timing information, usually 'rx_time' or empty (this means timing info is discarded)
samp_rate	Sampling rate at the input. Necessary to calculate the rx time of packets.
special_tags	A vector of strings denoting tags which shall be preserved (see Tag Handling)
header_padding	A number of items that is appended and prepended to the header.

---

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

• header_payload_demux.h