Design & Co-design of Embedded Systems

1. Design & Co-design of Embedded Systems Processes in SystemC Maziar Goudarzi

2. Today Program • Processes in SystemC • Elements in defining processes in SystemC • Some examples Design & Co-design of Embedded Systems

3. Process • Module • Basic unit of hierarchy (basic building block) in SystemC • Process • Basic unit of execution in SystemC • Processes are called to emulate the behavior of a target device or system Design & Co-design of Embedded Systems

4. Process • Basics • Basic unit of execution within SystemC • Emulate the behavior of target device • Are triggered by clock edges and/or signal expressions • Processes are not hierarchical • A process does not call another process • C++ allows this. Avoid using that. • Processes communicate through signals Design & Co-design of Embedded Systems

5. Process (cont’d) Module Input ports Process 1 IO port Process 2 Output ports Internal signal Design & Co-design of Embedded Systems

6. Process (cont’d) • Each process has • Sensitivity list • Execution type • A series of statements • A process is specified in two parts • Process declaration • Registers the process with the SystemC simulation kernel • Process definition • Specifies the C++/SystemC statements that the process executes Design & Co-design of Embedded Systems

7. Process (cont’d) • Process declaration • Sensitivity list + execution type • Must be given to SystemC simulation kernel to enable simulation • SystemC uses SC_MODULE constructor for this • Example: SC_CTOR(a_module) { SC_METHOD(a_process); sensitive<<a_port; } Design & Co-design of Embedded Systems

8. Process (cont’d) • Process definition • The series of statements (operations) to be executed • Includes • reading/writing ports, signals, and variables • Any valid C++ statement (display messages, calculations, etc.) • SystemC uses SC_MODULE member functions for this • SystemC simulation kernel calls this member function when a corresponding event happens • Example: SC_MODULE(a_module) { void a_process(void) { ... } SC_CTOR(a_module) { SC_METHOD(a_process); } }; Design & Co-design of Embedded Systems

9. Process (cont’d) • Communication between processes • SystemC (actually C++) allows to use SC_MODULE data members for this • Should we use that? Why? • Use signals (sc_signal<> type) to synchronize processes Design & Co-design of Embedded Systems

10. Declaring a Process • Process sensitivity list • List of events that trigger this process • Three types of sensitivity • sensitive • Any change of value on the port/signal triggers the process • sensitive_pos • A positive edge on the port/signal triggers the process • sensitive_neg • A negative edge on the port/signal triggers the process • General syntax • sensitive << port_1 << signal_1 << ... << port_n • sensitive_pos << port_1 << signal_1; • sensitive_neg << port_1 << signal_1; Design & Co-design of Embedded Systems

11. Declaring a Process (cont’d) • Process sensitivity list (cont’d) • The other syntax: • sensitive( port1 ); sensitive( signal1 ); • sensitive_pos( port1 ); sensitive_pos( sig1 ); • Sensitive_neg( port1 ); sensitive_neg( sig1 ); Design & Co-design of Embedded Systems

12. Declaring a Process (cont’d) • Process execution types in SystemC • Defines the way that the process is executed • Process types • Method • Thread • Clocked Thread Design & Co-design of Embedded Systems

13. Execution Types of Processes in SystemC • Three types of Process in SystemC • Methods • SC_METHOD process • Threads • SC_THREAD process • Clocked threads • SC_CTHREAD process Design & Co-design of Embedded Systems

14. SC_METHOD Process • Is called once, when events occur on its sensitivity list • Cannot suspend execution (i.e. cannotwait()) • wait() is a function in SystemC kernel. • What happens if you put a wait() in a SC_METHOD process? • Returns control to the caller (SystemC Kernel) Design & Co-design of Embedded Systems

15. Method Example:Packet Receiver void rcv::extract_id() { frame_type frame; frame = xin;if(frame.type==1) id = frame.ida;else id = frame.idb; } rcv id frame xin id #include “frame.h” SC_MODULE(rcv) { sc_in<frame_type> xin;sc_out<int> id; void extract_id(); SC_CTOR(rcv){ SC_METHOD(extract_id); sensitive(xin); }}; Design & Co-design of Embedded Systems

16. SC_THREAD Process • Declaration to SystemC kernel is the same as SC_METHOD process • Can be suspended and re-activated • wait() system call • Process is re-activated when an event occurs on process sensitivity list • General syntax: void a_thread_process() { // some statements (initialization) while ( 1) { // some other statements wait(); } } Design & Co-design of Embedded Systems

17. SC_THREAD Example:Traffic Light Controller SC_MODULE(traff) { sc_in<bool> roadsensor;sc_in<bool> clock; sc_out<bool> NSred;sc_out<bool> NSyellow;sc_out<bool> NSgreen;sc_out<bool> EWred;sc_out<bool> EWyellow;sc_out<bool> EWgreen; void control_lights(); Road Sensor SC_CTOR(traff){ SC_THREAD(control_lights); sensitive << roadsensor;sensitive_pos << clock; } }; Design & Co-design of Embedded Systems

18. SC_THREAD Example:Traffic Light Controller (cont’d) void traff::control_lights() { NSred = NSyellow = false; NSgreen = true; EWred = true; EWyellow = EWgreen = false; while (true) { while (roadsensor == false)wait(); NSgreen = false; NSyellow = true; NSred = false; for (i=0; i<5; i++)wait(); NSgreen = NSyellow = false; NSred = true; EWgreen = true; EWyellow = EWred = false; for (i= 0; i<50; i++)wait(); NSgreen = NSyellow = false; NSred = true; EWgreen = false; EWyellow = true; EWred = false; for (i=0; i<5; i++) wait(); Design & Co-design of Embedded Systems

19. SC_THREAD Example:Traffic Light Controller (cont’d) NSgreen = true; NSyellow = NSred = false; EWgreen = EWyellow = false; EWred = true; for (i=0; i<50; i++) wait(); } // while (true) } Design & Co-design of Embedded Systems

20. SC_THREAD Process (cont’d) • The SC_THREADprocess is the most general one • Implementing traff module with SC_METHODprocess requires defining several states • Performance issue • SC_THREAD simulation is slower than SC_METHOD Design & Co-design of Embedded Systems

21. SC_CTHREAD Process • The same as SC_THREAD, but is merely sensitive to edge of one clock • Results in better descriptions for synthesis • One major use: Implicit state machine • Implicit state machine vs. Explicit state machine • Additional waiting mechanisms • wait_until(<signal condition>) system call • Process is re-activated when the condition on the signals hold • timed wait, wait until condition with timeout (SystemC 2.0) Design & Co-design of Embedded Systems

22. addr 32 newaddr start data 32 data8 ready datardy SC_CTHREAD Example:Bus Controller SC_MODULE(bus) { sc_in_clk clock; sc_in<bool> newaddr; sc_in<sc_uint<32> > addr; sc_in<bool> ready; sc_out<sc_uint<32> > data; sc_out<bool> start; sc_out<bool> datardy; sc_inout<sc_uint<8> > data8; sc_uint<32> tdata; sc_uint<32> taddr; void xfer(); Bus Cntrlr Mem Cntrlr SC_CTOR(bus) { SC_CTHREAD(xfer, clock.pos()); datardy.initialize(true); } }; Design & Co-design of Embedded Systems

23. SC_CTHREAD Example:Bus Controller (cont’d) void bus::xfer() { while (true) { wait_until( newaddr.delayed() == true); taddr = addr.read(); datardy = false; data8 = taddr.range(7,0); start = true; wait(); data8 = taddr.range(15,8); start = false; wait(); data8 = taddr.range(23,16); wait(); data8 = taddr.range(31,24); wait(); wait_until(ready.delayed() == true); tdata.range(7,0)=data8; wait(); tdata.range(15,8)=data8; wait(); tdata.range(23,16)=data8; wait(); tdata.range(31,24)=data8; data = tdata; datardy = true; } } Design & Co-design of Embedded Systems

24. What we learned today • Processes in SystemC • Various sensitivity styles • Various execution styles • SystemC ver. 2.0 User’s Guide • Most of Chapter 4 Design & Co-design of Embedded Systems

25. Assignments • Today: Due date for Assignment 1 • Assignment 2: • Is put on the course web-page • Implement the traffic-light controller using only SC_METHOD • Model a file-server and its clients • Due date: • One week from now: Tuesday, Aban 3rd Design & Co-design of Embedded Systems

26. Complementary Notes:SystemC_Win • http://www.geocities.com/systemc_win/ Design & Co-design of Embedded Systems

27. Complementary Notes:SystemC_Win • http://www.geocities.com/systemc_win/ Design & Co-design of Embedded Systems