Understanding the Basics

• Tasks:
  • Execute a block of code sequentially.
  • Can have input, output, and inout arguments.
  • Can be called from other tasks, functions, or modules.
  • Can be blocking or non-blocking.
  • Can have automatic storage type for local variables, which is useful for recursive tasks.
• Functions:
  • Execute a block of code and return a value.
  • Can have input arguments only.
  • Can be called from other tasks, functions, or modules.
  • Must be blocking.
  • Cannot have automatic storage type for local variables.

Key Differences

Task Examples:

1. Delay Task:

   Code snippet

   task delay(input int delay_time);
       #delay_time;
   endtask
   

   This task can be used to introduce delays in simulations, often useful for timing-based verification.

2. Pulse Generation Task:

   Code snippet

   task pulse_gen(input int pulse_width, input int period);
       forever begin
           #pulse_width pulse = 1'b1;
           #(period - pulse_width) pulse = 1'b0;
       end
   endtask
   

   This task generates a periodic pulse signal, useful for driving testbench stimuli.

3. Error Reporting Task:

   Code snippet

   task error_report(string msg);
       $display("ERROR: %s", msg);
       $stop;
   endtask
   

   This task can be used to report errors and halt the simulation, aiding in debugging.

Function Examples:

1. Parity Check Function:

   Code snippet

   function bit parity_check(input bit [7:0] data);
       bit parity = 1'b0;
       for (int i = 0; i < 8; i++) begin
           parity ^= data[i];
       end
       return parity;
   endfunction
   

   This function calculates the parity bit of an 8-bit input.

2. Bitwise Reverse Function:

   Code snippet

   function bit [7:0] bit_reverse(input bit [7:0] data);
       bit [7:0] reversed_data;
       for (int i = 0; i < 8; i++) begin
           reversed_data[i] = data[7-i];
       end
       return reversed_data;
   endfunction
   

   This function reverses the bit order of an 8-bit input.

3. CRC Calculation Function:

   Code snippet

   function bit [15:0] crc_calc(input bit [31:0] data);
       // CRC calculation logic (e.g., using a CRC generator polynomial)
       // ...
       return crc_value;
   endfunction
   

   This function calculates the CRC checksum of a 32-bit input, useful for error detection and correction in communication systems.