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Process In SystemC

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Introduction

We saw in last chapter basic introduction to Processes. There are three types of processes in SystemC. Processes are not hierarchical, so no process will call another process directly. 

Processes can call methods and functions that are not processes. Processes have sensitivity lists, i.e. a list of signals that cause the process to be invoked, whenever the value of a signal in this list changes. Processes cause other processes to execute by assigning new values to signals in the sensitivity list of the other process.
Each of this processes will be discussed in detail in next few pages.

  • Methods
    • Edge Sensitive
    • Level Sensitive
  • Threads
  • Clocked Threads

Methods
Methods behaves like a function, when called it gets started and executes and returns execution back to calling mechanism. A method is called when ever the event in the sensitivity list changes. Like always block in Verilog. Triggering event in sensitive list can be either edge sensitive or level sensitive.
Note :
 Sensitive list signals which trigger a process can be a signal or local variable or port.

The input signals that cause the process to reactivate are specified by the sensitivity list. The sensitivity list is specified in the module constructor

Example Methods

  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     // At every rising edge of clock we check if reset is active

 24     // If active, we load the counter output with 4'b0000

 25     if (reset.read() == 1) {

 26       count =  0;

 27       counter_out.write(count);

 28     // If enable is active, then we increment the counter

 29     } else if (enable.read() == 1) {

 30       count = count + 1;

 31       counter_out.write(count);

 32     }

 33   } // End of function incr_count

 34

 35   // Below functions prints value of count when ever it changes

 36   void print_count () {

 37     cout<<"@" << sc_time_stamp() <<

 38       " :: Counter Value "<endl;

 39   }

 40

 41   // Constructor for the counter

 42   // Since this counter is a positive edge trigged one,

 43   // We trigger the below block with respect to positive

 44   // edge of the clock and also when ever reset changes state

 45   SC_CTOR(first_counter) {

 46     // Edge and level sensitive

 47     SC_METHOD(incr_count);

 48     sensitive << reset;

 49     sensitive << clock.pos();

 50     // Level Sensitive method

 51     SC_METHOD(print_count);

 52     sensitive << counter_out;

 53   } // End of Constructor

 54

 55 }; // End of Module counter

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