probe_ber :
A probe for measuring the bit-error rate of a data stream.

The probe_ber primitive measures the bit-error rate of a data stream in by comparing it either with an external reference data stream in_ref (with mode=”ext” or “in”) or with an internal PRBS reference (with mode=”int” or “prbs”). In case of using an internal PRBS reference, the parameter length defines the LFSR length N, generating a pseudo-random bit sequence with a length of 2^N-1. The value range of length is 3~128 (default: 7). The primitive can also verify a parallel stream of M-bit pseudo-random sequences, where the bit-width M is set by the parameter width.

The parameter trig_mode defines whether the inputs in and in_ref are sampled at the positive edge (1), negative edge (-1), or both edges (0) of the input clk. By default, the inputs are sampled at the negative edge of clk (-1), assuming the data transitions are aligned with the positive edges of clk.

The parameter filename sets the name of the waveform file, of which extension determines the waveform format (e.g. “.jez” for JEZ and “.fsdb” for FSDB). In case of recording in JEZ format, the parameter format defines whether the data are recorded in a binary (“jezbinary”) or ascii (“jezascii”) format. The parameters start and stop define when the recording begins and ends, respectively.

Input/Output Terminals

Name	I/O	Type	Description
in	input	xbit	input data
in_ref	input	xbit	reference data
clk	input	xbit	clock

Parameters

Name	Type	Default	Unit	Description
filename	string	“xmodel.jez”	None	output filename
format	string	“jezbinary”	None	format version
start	real	0.0	seconds	abs. time to start recording
stop	real	-1.0	seconds	abs. time to stop recording
mode	string	“ext”	None	reference source
length	integer	7	None	reference LFSR length
width	integer	1	None	input bit-width
trig_mode	integer	-1	None	triggering mode