WWW.TESTBENCH.IN - Verilog for Verification

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Specman E
Interview Questions

TASK BASED TB

Task And Function Based Tb:

Task based verification is more flexible over all the above approaches. All the operations in are done using takes and functions. The task based BFM is extremely efficient if the device under test performs many calculations. Each task or function focuses on one single functionality. Verification of DUT using the task based testbench is faster. Using tasks makes it possible to describe structural testbenchs. These tasks can be ported without much effort.

EXAMPLE:
task write(input integer data,input integer address);
begin
   @(posedge clock);
   read_write = 1;
   address = $random;
   data = $random;
end
endtask

task read(input integer address,output integer data);
begin
   @(posedge clock);
   read_write = 0;
   address = $random;
   // Do some operation to get data
end
endtask

Now lets see how to develop the senarious.

1) 10 write operations.

initial
   repeat(10)
   write($random,$random);

2) 10 read operations

initial
   repeat(10)
   read($random,data);

3) Alternate read and write operations.

initial
   repeat(10)
   begin
      write($random,$random);
      read($random,data);
   end

4) Do the write and read the same location.

initial
    begin
        write(10,20);
        read (10,data);
    end

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