SIM::lfsr Class Reference

linear feedback shift register
Core function: SIM::lfsr.generate()
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Inheritance diagram for SIM::lfsr:

Public Member Functions
	lfsr ()
	~lfsr ()
void	set_poly (const bvec &bpoly)
void	set_prbs (int M)
void	set_symbol_size (int W)
void	set_reset_state (const bvec &binit)
void	set_output (const bvec &yout)
void	set_rev_flag (bool flag)
bvec	get_poly ()
bvec	get_state ()
int	get_symbol_size ()
bvec	get_reset_state ()
bvec	get_output ()
bool	get_rev_flag ()
bmat	generate (const bvec &ce)

Detailed Description

linear feedback shift register
Core function: SIM::lfsr.generate()

itpp::LFSR derived class with clocked interface

Note

itpp::LFSR is in the Fibonacci form
Example: 1+X3+X4 for PRBS sequence = 2^4-1
set_prbs(4) -> set_poly with a bpoly=bvec("1 0 0 1 1");

      1 +     X3+X4
      0  1  2  3  4
     [1  0  0  1  1]

By definition there is no X^0 cell - first cell - state[0] is represented by X^1.
Threfore for LFSR of lenght N, state is bvec with lenght of (N-1)
The implementation is like J.83B standard p.9 -> PRBS randomizer
For one active tick ce[i] a single symbol represented as bvec with symbol_size = W bits is created:
y[i,:] = [x0(W-1), x0(W-2),...,x0(1), x0(0)] (default: reversed = true - x0(0) is oldest bit as for a generation time)
where each x0 bit is calculated as:
{ bin x0 = state[0:N-1] * bpoly[1:N]; state.shift_right(x0); return x0; }
Output y for ce[M] ticks is bmat with a size y = bmat[M,W]

rev_flag controls if output is reversed, default value of rev_flag is TRUE

when output is revesed symbols s[k+1] = [b[n+5],b[n+4],b[n+3]], s[k] = [b[n+2],b[n+1],b[n]]
can be easily be used in BERT synchronization [s[k+1]|s[k]], because time scale is continous

Constructor & Destructor Documentation

SIM::lfsr::lfsr ( )

inline

SIM::lfsr::~lfsr ( )

inline

Member Function Documentation

bmat SIM::lfsr::generate

(

const bvec &

ce

)

for active clock ticks [ce] generate one symbol (W bits) in output bmat y

Parameters

ce	- [bvec] - clock enable vector - sizeof(ce)=N

Returns

y - [bmat] - output symbols matrix - sizeof(y)=[N,W]

bvec SIM::lfsr::get_output

(

void

)

get initial/idle output vector

Returns

- [bvec] y0 ,sizeof(y0)=W

bvec SIM::lfsr::get_poly

(

void

)

get connection poly

Returns

- [bvec] y0 = yout

bvec SIM::lfsr::get_reset_state

(

)

get reset state binary vector

Returns

- [bvec] s0

bool SIM::lfsr::get_rev_flag

(

)

get value of rev_flag

Note

when rev_flag is true, output is bit reversed, default value is true,

Returns

- [bool] rev_flag

bvec SIM::lfsr::get_state

(

void

)

get state binary vector

Note

state is reversed when rev_flag is set

Returns

- [bvec] state

int SIM::lfsr::get_symbol_size

(

void

)

get symbol size

Returns

- [int] W

void SIM::lfsr::set_output

(

const bvec &

yout

)

sets initial/idle output vector

Note

yout is a bvec of symbol size (W) length

Parameters

[in]

yout

- [bvec] y0 = yout

void SIM::lfsr::set_poly

(

const bvec &

bpoly

)

set feedback poly [g0,g1,...,gr] =1+g1*D+g2*D^2+...+gr*D^r
and set default value s0=[10000000...] for reset state and executes reset !

Note

set_poly() or set_prbs() are minimal set-up for symbol_size == 1

- internally LSB is leftmost, output might be reversed if rev_flag is true

Parameters

[in]

bpoly

- [bvec] feedback poly

void SIM::lfsr::set_prbs

(

int

M

)

set predefined bpoly for PRBS defined by PRBS sequecne 2^M-1
and execute set_poly() for selected bpoly

Note

set_poly() or set_prbs() and set_symbol_size() are minimal set-up

- bpoly are defined for [3..9,15,23,31] - source wikipedia, xilinx xapp052.pdf

Parameters

[in]

M

- [int] power of PRBS sequence size = 2^M-1

void SIM::lfsr::set_reset_state

(

const bvec &

binit

)

sets value of internal forced by reset s0

Note

- only sets variable, does not executes RESET

Parameters

[in]

binit

- [bvec] initial internal state after RESET

void SIM::lfsr::set_rev_flag

(

bool

flag

)

sets value of rev_flag

Note

when rev_flag is true, output is bit reversed, default value is true,

Parameters

[in]

flag

- [bvec] rev_flag = flag

void SIM::lfsr::set_symbol_size

(

int

W

)

set symbol_size

Note

set_poly() or set_prbs() and set_symbol_size() are minimal set-up

- for one ce tick LFSR is shifted W times to create on symbol

Parameters

[in]

W

- [int] number of LFSR shifts and bits in output bmat for one ce tick

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

• C:/jobs/vcc/itpp_sci/include/sim/sim_lfsr.hpp
• C:/jobs/vcc/itpp_sci/sim_lib/code/sim_lfsr.cpp