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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