GNU Radio Manual and C++ API Reference  3.10.9.1
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gr::digital::header_payload_demux Class Reference

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

#include <gnuradio/digital/header_payload_demux.h>

Public Types

typedef std::shared_ptr< header_payload_demuxsptr
 
- Public Types inherited from gr::block
enum  work_return_t { 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
 ~block () override
 
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 representation 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...
 
void set_blkd_input_timer_value (unsigned int timer_value_ms)
 DEPRECATED Configure the timer set when input is blocked port. More...
 
unsigned int blkd_input_timer_value ()
 DEPRECATED Returns timer value set when input is blocked. More...
 
void allocate_detail (int ninputs, int noutputs, const std::vector< int > &downstream_max_nitems_vec, const std::vector< uint64_t > &downstream_lcm_nitems_vec, const std::vector< uint32_t > &downstream_max_out_mult_vec)
 Allocate the block_detail and necessary output buffers for this block. More...
 
buffer_sptr replace_buffer (size_t src_port, size_t dst_port, block_sptr block_owner)
 Replace the block's buffer with a new one owned by the block_owner parameter. 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 () const
 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) override
 Set the thread's affinity to processor core n. More...
 
void unset_processor_affinity () override
 Remove processor affinity to a specific core. More...
 
std::vector< int > processor_affinity () override
 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 (const std::string &level) override
 Set the logger's output level. More...
 
std::string log_level () override
 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)
 
 ~basic_block () override
 
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 () override
 
void post (pmt::pmt_t which_port, pmt::pmt_t msg) override
 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)
 
buffer_sptr allocate_buffer (size_t port, int downstream_max_nitems, uint64_t downstream_lcm_nitems, uint32_t downstream_max_out_mult)
 Allocate a buffer for the given output port of this block. Note that the downstream max number of items must be passed in to this function for consideration. More...
 
- 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)
 
template<typename Derived >
std::shared_ptr< Derived > shared_from_base ()
 This is meant to be called by derived classes (e.g. block) to get a shared pointer internally. This is needed because std::enable_shared_from_this doesn't seem to work with derived classes in an inheritance hierarchy. More...
 
- Protected Attributes inherited from gr::block
std::vector< long > d_max_output_buffer
 
std::vector< long > d_min_output_buffer
 
unsigned int d_blkd_input_timer_value = 250
 
gr::thread::mutex d_setlock
 
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
 
gr::logger_ptr d_logger
 
gr::logger_ptr d_debug_logger
 Default logger. More...
 
msg_queue_map_t msg_queue
 Verbose logger. More...
 
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 distinguishes 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

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_lenNumber of symbols per header
items_per_symbolNumber of items per symbol
guard_intervalNumber of items between two consecutive symbols
length_tag_keyKey of the frame length tag
trigger_tag_keyKey of the trigger tag
output_symbolsOutput symbols (true) or items (false)?
itemsizeItem size (bytes per item)
timing_tag_keyThe name of the tag with timing information, usually 'rx_time' or empty (this means timing info is discarded)
samp_rateSampling rate at the input. Necessary to calculate the rx time of packets.
special_tagsA vector of strings denoting tags which shall be preserved (see Tag Handling)
header_paddingA number of items that is appended and prepended to the header.

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