delay_sel :
A selectable transport delay for xreal-typed signals

The delay_sel primitive models a transport delay for xreal-typed signals, which can be selected from a set of delays by a wire-type selection signal sel. With this primitive, one can describe a transport delay element of which delay can vary with a set of digital input values.

With the width of the input sel equal to k, as specified by the parameter width_sel, the primitive can have up to 2^k transport delays to select from. Each transport delay is indexed by an integer ranging from 0 to 2^k-1, which corresponds to the unsigned integer value of the input sel[k-1:0].

The parameters indices and delay together describe the set of transport delays. First, the parameter indices is an integer-type array that lists the indices of the transport delays in the order that they are defined in the parameter delay. The indices may be listed in an arbitrary order and may not span a complete set, but each index must be within the range of 0~2^k-1. For example, ‘{0, 3, 1} is possible when k=2. The special value of ‘{-1} is equivalent to a complete set of indices listed as ‘{0, 1, 2, …, 2^k-1}.

On the other hand, the parameter delay is a real-type array listing the transport delay values in seconds, of which indices are listed in the parameter indices. For synchronization reasons, the transport delay values must be at least a unit timestep.

For illustration, the following example describes two transport delays with index 0 and 1, respectively. The transport delay with index 0 is 5ns and the transport delay with index 1 is 2.5ns.

    indices = '{0, 1}
    data = '{5e-9, 2.5e-9}

When the parameter indices does not list a complete set of indices, the undefined transport delays are assumed to be 0.0.

When the parameter filename is defined, the primitive reads the named file that defines the parameter values in Python format. For the above example, the values of the parameters indices and delay can be defined within a file as below:

    indices = [0, 1]
    data = [5e-9, 2.5e-9]

Input/Output Terminals

Name	I/O	Type	Description
out	output	xreal	output signal
in	input	xreal	input signal
sel	input	wire	selection signal (binary-coded)

Parameters

Name	Type	Default	Unit	Description
width_sel	integer	1	None	width of selection bits
indices	int array	‘{0}	None	list of delay indices
delay	real array	‘{0.0}	seconds	list of transport delays
filename	string	“”	None	parameter definition file