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Process In SystemC Part III

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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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