Threads are second kind of process, which when called keeps executing or waiting for some event to occur. Conditions that enable this processes can be event triggered, like posedge of clock.

Thread Process can be suspended and reactivated. The Thread Process can contain wait() functions that suspend process execution until an event occurs on one of the signals the process is sensitive to. An event will reactivate the thread process from the statement the process was last suspended. The process will continue to execute until the next wait().

  1 //-----------------------------------------------------
  2 // This is my second Systemc Example
  3 // Design Name : first_counter
  4 // File Name : first_counter.cpp
  5 // Function : This is a 4 bit up-counter with
  6 // Synchronous active high reset and
  7 // with active high enable signal
  8 //-----------------------------------------------------
  9 #include "systemc.h"
 10 
 11 SC_MODULE (first_counter) {
 12   sc_in_clk     clock ;      // Clock input of the design
 13   sc_in<bool>   reset ;      // active high, synchronous Reset input
 14   sc_in<bool>   enable;      // Active high enable signal for counter
 15   sc_out<sc_uint<4> > counter_out; // 4 bit vector output of the counter
 16 
 17   //------------Local Variables Here---------------------
 18   sc_uint<4>	count;
 19 
 20   //------------Code Starts Here-------------------------
 21   // Below function implements actual counter logic
 22   void incr_count () {
 23     // For threads, we need to have while true loop
 24     while (true) { 
 25       // Wait for the event in sensitivity list to occure
 26       // In this example - positive edge of clock
 27       wait();
 28       if (reset.read() == 1) {
 29         count =  0;
 30         counter_out.write(count);
 31       // If enable is active, then we increment the counter
 32       } else if (enable.read() == 1) {
 33         count = count + 1;
 34         counter_out.write(count);
 35       }
 36     }
 37   } // End of function incr_count
 38 
 39   // Below functions prints value of count when ever it changes
 40   void print_count () {
 41     while (true) {
 42       wait();
 43       cout<<"@" << sc_time_stamp() <<
 44         " :: Counter Value "<<counter_out.read()<<endl;
 45     }
 46   }
 47 
 48   // Constructor for the counter
 49   // Since this counter is a positive edge trigged one,
 50   // We trigger the below block with respect to positive
 51   // edge of the clock
 52   SC_CTOR(first_counter) {
 53     // Edge sensitive to clock
 54     SC_THREAD(incr_count);
 55     sensitive << clock.pos();
 56     // Level Sensitive to change in counter output
 57     SC_THREAD(print_count);
 58     sensitive << counter_out;
 59   } // End of Constructor
 60 
 61 }; // End of Module counter

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