CODEWITHSUNDEEP
verilogsystem-verilog
ssrinivas
ssrinivas

Reputation: 23

Systemverilog: $realtime display for different timescale precision

I was trying to print the $realtime for the following timescale setting:

`timescale 1ns/10ps 
initial begin        
    #10;
    $display(" %0t",$realtime);
    $display($realtime);
end

The result that gets prints is:

1000
10

I am just curious as to what is different in using format specifier in printing realtime? Correct me if I am wrong. I believe it is printing 1000 (10 *10ps = 1000 ns) because of the time precision. But what is the reason for the difference?

Upvotes: 2

Views: 15158

Answers (1)

Matthew
Matthew

Reputation: 13987

The $timeformat system task is used to set the format of the output when the %t format specifier is used. It should only be called once (if it is called more than once, the last call will override the previous ones). It has 4 parameters: they are:

$timeformat(<units>, <precision>, <suffix>, minimum field width>);

units               : log base 10 of the unit (eg -9 is ns)
precision           : the number of decimal places
suffix              : a string (eg "ns")
minimum field width : the minimum field width

$display(" %0t",$realtime); is printing the time according to the time format set up by the $timeformat system task. As you haven't called the $timeformat system task, the default values are used. They are:

units               : the simulation precision (10ps in your case)
precision           : 0
suffix              : null string
minimum field width : 20

$display($realtime); displays the value returned from the $realtime system function as a decimal integer - 10 in your case.

Upvotes: 5

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