[HDL] Value Change Dump (VCD) File

VDC 파일 아래에 여차저차 설명이 있다. 
제일 많이 쓰는 곳은 테스트벡터를 전달해 줄 때 서로서로 포맷을 맞춰줘야 하는데, 그나마 별 신경쓰지 않고 vcd 파일로 전달 해 주면 대부분 변경해서 사용이 가능하다. 이정도 노력은 해줘야 테스트 하우스 혹은 디자인 하우스에서 좋아하겠지 ^~^

원본 : http://verilog.renerta.com/mobile/source/vrg00056.htm

Value Change Dump (VCD) File

The Value change dump (VCD) file contains information about any value changes on the selected variables. Value change dump file can be used for hierarchical monitoring of all signal changes within design modules.

$dumpfile(filename)

This task is used to specify the VCD file name. The filename parameter is optional. If it is not given, then the file will be named "Verilog.dump”.

$dumpvars(level, list_of_variables_or_modules)

This task is used to specify which variables should be dumped. Both parameters are optional and if none are used, then all variables will be dumped.

If level = 0, then all variables within the modules from the list will be dumped. If any module from the list contains module instances, then all variables from these modules will also be dumped.

If level = 1, then only listed variables and variables of listed modules will be dumped.

$dumpoff

This task stops the dumping of variables. All variables are dumped with x value and all next changes of variables will not be dumped.

$dumpon

This task starts previously stopped dumping of variables.

$dumpall

When this task is used, then the current value of all dumped variables will be written to file.

$dumplimit(filesize)

This task can set the maximum size of the VCD file.

$dumpflush

This task can be used to make sure that all changes of dumped variables are written to file.

사용 예 : 이걸 보면 대충 파악가능

module top;
reg a, b;
wire y;
assign y = a & b;

always begin
  a = 1'b0;
  #10;
  a = 1'b1;
  #10;
  a = 1'bx;
  #10;
end

always begin
  b = 1'b0;
  #30;
  b = 1'b1;
  #30;
  b = 1'bx;
  #30;
end

initial begin
  $dumpfile("test.txt");
  $dumpvars(1,a,y);
  #200;
  $dumpoff;
  #200;
  $dumpon;
  #20;
  $dumpall;
  #10;
  $dumpflush;
end

endmodule

The dumpfile will contain only changes of 'a' and 'y' variables. After 200 time units, dumping will be suspended for 200 time units. Next, dumping will start again and after 20 time units, all variables will be dumped.