verilog code to decide release time

[vikas.m0502]

Hi,

I am trying to release a signal at specific time. For that I need to write a small code in verilog.
Condition is :

if write_select is 0 for greater than 16ns then release Q after 16ns when write_select goes high.

Please let me know if need more clarification.

Thanks in advance.
Vikas

 

[Mohammed_Verification]

Hi vikas.m0505,

Refer force and release topic under this link https://www.asic-world.com/verilog/vbehave1.html
Hope it may be helpful.

Regards,
Mohammed.

 

[dave_59]

Perhaps you better define what you mean by "release" as it a keyword in Verilog and may have nothing to do with what you are asking.

And is this something you are trying to design, or is this to stimulate a design under test.

 

[vikas.m0502]

Hi Mohammed,
Thanks for your reply, but whatever is in that link i already know.
My main problem is how to give condition with respect to signal's width.


Hi Dave,
It is the same 'release' what we use as keyword.
Yes, I need this forcing for simulation purpose.
Like I said before, I have no issue with 'force' or 'release', but how to right the condition for releasing some signal based on its width.

Thanks
Vikas

 

[vardan]

if write_select is 0 for greater than 16ns then release Q after 16ns when write_select goes high

Task is not clear. >16ns or when write_select goes high?
I would suggest using time variable
See example code below. Adjust time_limit parameter to the timescale.

`timescale 1ns/1ns

module test1();
parameter hi = 1'b1, lo = 1'b0;
parameter time_limit = 16;
reg write_sel;
time t1, t2, time_diff;

initial
begin
	write_sel = hi;
	t1 = 0; t2 = 0; time_diff = 0;
	#10 write_sel = lo;
	#10 write_sel = hi;
	#10 write_sel = lo;
	#20 write_sel = hi;
	#10 write_sel = hi;
	#10 write_sel = hi;
	$stop;
end

always @(write_sel)
	begin
		if(write_sel)
			t2 = $time;
		else if (!write_sel)
			t1 = $time;
		if(t2>t1)
		begin
			time_diff = t2 - t1;
			if(time_diff > time_limit)
				$display("Time to release Q, duration = %d", time_diff);
		end
	end

endmodule

 

[vikas.m0502]

Hi vardan,

Thanks for your reply.
But your code is too lengthy. I want something precise.

What I want to do is :
If write_sel is >16ns
then whenever it goes high, 16ns after that release the force.
Means as soon as write_sel goes high, 16ns after that i have to release.
For this I need the condition which relates the width of write_sel, because write_sel toggles many times but only this time it is low for more than 16ns.

Thanks,
Vikas

 

[vardan]

always @(negedge write_sel)
		t2 = $time;

always @(posedge write_sel)
	if (($time-t2) > time_limit)
    $display("\n\tTime to release Q");

It's not a case to use $width. See if you can optimize the code.