Verilog - System Tasks

System Tasks

System tasks are available to handle simple I/O, and various design measurement functions. All system tasks are prefixed with $ to distinguish them from user tasks and functions. This section presents a short list of the most often used tasks. It is by no means a comprehensive list.

  • $display - Print to screen a line followed by an automatic newline.
  • $write - Write to screen a line without the newline.
  • $swrite - Print to variable a line without the newline.
  • $sscanf - Read from variable a format-specified string. (*Verilog-2001)
  • $fopen - Open a handle to a file (read or write)
  • $fdisplay - Write to file a line followed by an automatic newline.
  • $fwrite - Write to file a line without the newline.
  • $fscanf - Read from file a format-specified string. (*Verilog-2001)
  • $fclose - Close and release an open file handle.
  • $readmemh - Read hex file content into a memory array.
  • $readmemb - Read binary file content into a memory array.
  • $monitor - Print out all the listed variables when any change value.
  • $time - Value of current simulation time.
  • $dumpfile - Declare the VCD (Value Change Dump) format output file name.
  • $dumpvars - Turn on and dump the variables.
  • $dumpports - Turn on and dump the variables in Extended-VCD format.
  • $random - Return a random value.

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