Clocked Threads
SC_CTHREAD process is different from the SC_THREAD process in a number of ways. First the SC_CTHREAD process specifies a clock object.

 When other process types are described in a module constructor they only have the name of the process specified, but the SC_CTHREAD process has the name of the process and the clock that triggers the process. An SC_CTHREAD does not have a separate sensitivity list like the other process types. The sensitivity list is just the specified clock edge. The SC_CTHREAD process will be activated whenever the specified clock edge occurs. In this example the positive edge of the clock is specified so process incr_count will execute on every positive edge of the clock.

Note :SC_CTHREAD can have only one bit wide ports as trigger.
Example Clocked Threads

  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 "<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     // cthreads require to have thread name and triggering 

 54     // event to passed as clock object

 55     SC_CTHREAD(incr_count, 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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