GNU Radio 3.7.1 C++ API
Public Member Functions
gr::digital::lfsr Class Reference
Miscellaneous

Fibonacci Linear Feedback Shift Register using specified polynomial mask. More...

#include <lfsr.h>

List of all members.

Public Member Functions

 lfsr (uint32_t mask, uint32_t seed, uint32_t reg_len)
unsigned char next_bit ()
unsigned char next_bit_scramble (unsigned char input)
unsigned char next_bit_descramble (unsigned char input)
void reset ()
void pre_shift (int num)
int mask () const

Detailed Description

Fibonacci Linear Feedback Shift Register using specified polynomial mask.

Generates a maximal length pseudo-random sequence of length 2^degree-1

Constructor: digital::lfsr(int mask, int seed, int reg_len);

Parameters:
mask- polynomial coefficients representing the locations of feedback taps from a shift register which are xor'ed together to form the new high order bit.

Some common masks might be: x^4 + x^3 + x^0 = 0x19 x^5 + x^3 + x^0 = 0x29 x^6 + x^5 + x^0 = 0x61

Parameters:
seed- the initialization vector placed into the register durring initialization. Low order bit corresponds to x^0 coefficient -- the first to be shifted as output.
reg_len- specifies the length of the feedback shift register to be used. Durring each iteration, the register is rightshifted one and the new bit is placed in bit reg_len. reg_len should generally be at least order(mask) + 1

see http://en.wikipedia.org/wiki/Linear_feedback_shift_register for more explanation.

next_bit() - Standard LFSR operation

Perform one cycle of the LFSR. The output bit is taken from the shift register LSB. The shift register MSB is assigned from the modulo 2 sum of the masked shift register.

next_bit_scramble(unsigned char input) - Scramble an input stream

Perform one cycle of the LFSR. The output bit is taken from the shift register LSB. The shift register MSB is assigned from the modulo 2 sum of the masked shift register and the input LSB.

next_bit_descramble(unsigned char input) - Descramble an input stream

Perform one cycle of the LFSR. The output bit is taken from the modulo 2 sum of the masked shift register and the input LSB. The shift register MSB is assigned from the LSB of the input.

See http://en.wikipedia.org/wiki/Scrambler for operation of these last two functions (see multiplicative scrambler.)

Constructor & Destructor Documentation

gr::digital::lfsr::lfsr ( uint32_t  mask,
uint32_t  seed,
uint32_t  reg_len 
) [inline]

Member Function Documentation

int gr::digital::lfsr::mask ( ) const [inline]
unsigned char gr::digital::lfsr::next_bit ( ) [inline]

Referenced by pre_shift().

unsigned char gr::digital::lfsr::next_bit_descramble ( unsigned char  input) [inline]
unsigned char gr::digital::lfsr::next_bit_scramble ( unsigned char  input) [inline]
void gr::digital::lfsr::pre_shift ( int  num) [inline]

Rotate the register through x number of bits where we are just throwing away the results to get queued up correctly

References next_bit().

void gr::digital::lfsr::reset ( ) [inline]

Reset shift register to initial seed value

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