RE: When does w change?

I would have thought there would be an event on e at every timestep. All
the @cross does is make sure you get one at the moment the crossing
occurs - i.e. without the @cross there will be some delay between the
time sin($abstime) crosses 0 and the assign is performed.

Kev.

-----Original Message-----
From: owner-verilog-ams@eda.org [mailto:owner-verilog-ams@eda.org] On
Behalf Of Jonathan David
Sent: Friday, February 11, 2005 4:12 PM
To: verilog-ams@eda.org
Subject: RE: When does w change?

 It would never have occurred to me to TRY that syntax.
What I would have used would be..
module x;
  real e;
  reg d = 0;
  wire w;
  analog e = sin($abstime);
  always @(cross(e)) d = (e > 0.0);
  assign w = d;
endmodule

Which I think is your intent..
and should enable you to answer the question.
Without the @cross, there is never an EVENT to drive the update in the
digital side.

Jonathan David Mixed-Signal IC
jbdavid@cadence.com Ph (408)894-2646

-----Original Message-----
From: owner-verilog-ams@eda.org [mailto:owner-verilog-ams@eda.org] On
Behalf Of Kevin Cameron
Sent: Friday, February 11, 2005 3:58 PM
To: Bakalar, Kenneth; verilog-ams@eda.org
Subject: RE: When does w change?

I would have thought the assign would be evaluated anytime e changes,
which begs the question when does the analog statement get evaluated? -
Is there a maximum/minimum timestep that applies here?

Kev.

-----Original Message-----
From: owner-verilog-ams@eda.org [mailto:owner-verilog-ams@eda.org] On
Behalf Of Bakalar, Kenneth
Sent: Friday, February 11, 2005 3:00 PM
To: verilog-ams@eda.org
Subject: When does w change?

All,

Here is a puzzle. At what series of simulation times is the process
associated with the "assign" executed?

module x;
  real e;
  wire w;
  analog e = sin($abstime);
  assign w = (e > 0.0);
endmodule

"6.1.2 The continuous assignment statement [Verilog 2001]

...Assignments on nets shall be continuous and automatic. This means
that whenever an operand in the righthand side expression changes value,
the whole right-hand side shall be evaluated and if the new value is
different from the previous value, then the new value shall be assigned
to the left-hand side..."

Regards,
Ken
Received on Fri Feb 11 17:50:50 2005