replay_xbit :
A reproducer of an xbit-type signal stored in a waveform file.

The replay_xbit primitive replays an xbit-typed signal stored in a waveform file. This primitive is useful when composing a testbench that feeds the previously-collected simulation results as inputs to a new device-under-test (DUT).

For instance, to replay a signal with a hierarchical name of X1.Y1.a stored in a waveform file named mywaves.fsdb, you can instantiate this replay_xbit primitive with the parameters filename and signal defined as below:

    xbit a;
    replay_xbit #(.filename("mywaves.fsdb"), .signal("X1.Y1.a")) inst_a (.out(a));

In case the waveform file stores the signal as a multi-bit vector, you must connect the primitive’s output to an equal-width xbit vector and specify its bit width using the parameter width. For instance, the following example replays an 8-bit vector signal X1.Y1.b[7:0] stored in the waveform file.

    xbit [7:0] b;
    replay_xbit #(.filename("mywaves.fsdb"), .signal("X1.Y1.b[7:0]"), .width(8)) inst_b (.out(b));

Instead of replaying the whole waveform, you can replay a selected part of the waveform, of which start and stop time positions are defined by the parameters start and stop, respectively. For instance, if the parameter start is 100e-9 and stop is 200e-9, the replay_xbit primitive reproduces the waveform starting from the 100ns-position to the 200ns-position of the waveform, starting from the simulation time of zero. If the parameter start has a negative time value or the parameter delay has a positive time value, the primitive does not start replay until the simulation time of abs(start)+delay is elapsed and outputs a value defined by the parameter init_value or the initial value of the waveform at time=0 until then. On the other hand, when the primitive stops replay because it reaches the end of the waveform or a positive time value defined by the parameter stop, the primitive outputs a value defined by the parameter final_value or holds the last value of the waveform until the simulation ends.

NOTE: The current release supports the replay of waveforms only in FSDB-format files.

Input/Output Terminals

Name	I/O	Type	Description
out	output	xbit	signal output

Parameters

Name	Type	Default	Unit	Description
filename	string	“”	None	waveform filename
signal	string	“”	None	signal name
width	int	1	None	signal bit-width
start	real	0.0	seconds	waveform time position to start replay
stop	real	-1.0	seconds	waveform time position to stop replay
delay	real	0.0	seconds	initial_delay before replay starts
init_value	logic	1’bz	None	initial value before replay starts
final_value	logic	1’bz	None	final value after replay stops