SystemC tutorial

• Introduction
• Repository structure
• Installation
• Ports
• sc_main
• sc_module
• sc_constructor(sc_ctor)
• Threads

What is SystemC

SystemC is a collection of classes and libraries that provide event driven simulation for a system modeling language called SystemC. Its a way to enable hardware modeling functionality within C++. SystemC is based on C++, which gives it speed and flexibility. TLM 2.0 is not covered here, but it comes inside SystemC folder you download.

Being based on C++, SystemC doesnt require any special EDA tool in order to use it. All you need is a C++ compiler that you can link your installation to.

Knowledge of C++ and basic hardware concepts(like clocks, gates and waveforms) is required in order to understand this.

Repository structure

This repository contains few sub-directoires

 SystemC-tutorial             # top directory
 └── examples                 # directory with examples
     ├── counter              # counter example with Makefile, not syntesizable by HLS tools
     ├── hello-world          # hello-world example with Makefile, not syntesizable by HLS tools
     └── synthesizable        # directory containing examples synthesizable by HLS tools

Installation

Dependencies:

• For Debian/Ubuntu and Ubuntu based distros

sudo apt install build-essential make wget git gcc g++

• For Arch, Manjaro and other Arch based distros

sudo pacman -S make wget git gcc g++

SystemC can be downloaded, free of charge, from Accellera's website.

Steps:

1. Open terminal and type

wget http://www.accellera.org/images/downloads/standards/systemc/systemc-2.3.3.gz

This downloads the SystemC tarball

2. Unpack the package and make directories

tar -xzf systemc-2.3.3.gz
sudo mkdir /usr/local/systemc-2.3.3/
cd systemc-2.3.3 && mkdir objdir && cd objdir

3. Final installation

sudo ../configure --prefix=/usr/local/systemc-2.3.3/
sudo make -j$(nproc)
sudo make install

Compile the program

For Linux

First clone this repo

git clone https://github.com/AleksandarKostovic/SystemC-tutorial.git

Then run the command to compile SystemC into executable called hello

g++ -I. -I /usr/local/systemc-2.3.3/include -L. -L/usr/local/systemc-2.3.3/lib-linux64 -Wl,-rpath=/usr/local/systemc-2.3.3/lib-linux64 -lsystemc -lm -o hello hello.cpp

In the examples i provided makefiles so all you have to do is type make in the example directory

Now, type ./hello to run the exectutable and you should get this:

        SystemC 2.3.3-Accellera --- Nov 15 2018 12:20:10
        Copyright (c) 1996-2018 by all Contributors,
        ALL RIGHTS RESERVED
Hello World!

Keywords introduced and some building concepts

Ports

Ports in SystemC are similar to those found in HDL's. They are either inputs, outputs or bidirectional ports. They are desined as:

• sc_in - Input port
• sc_out - Output port
• sc_inout - Bidirectional port

There are ports for clocks like sc_in_clk but it is reccomend to use regular ports even for clock. For example sc_in<bool> clock is just an input port with boolean nature. Its either high or low(when thinking about clock) - 1 or 0.

sc_main

sc_main is the master function. When building a system based on SystemC, sc_main is going the whole system's main function. You can build multiple functions, but sc_main must be present. Like in hello world example:

#include <systemc.h>

SC_MODULE (hello) {  // module named hello
  SC_CTOR (hello) {  //constructor phase, which is empty in this case
  }

  void say_hello() {
    std::cout << "Hello World!" << std::endl;
  }
};

int sc_main(int argc, char* argv[]) {
  hello h("hello");
  h.say_hello();
  return 0;
}

We have two functions. The say_hello is responsable for outputing text, while the sc_main is passing the say_hello function and returning 0(success).

SC_MODULE

SC_MODULE is meant to be a declaration of a complete module/part. It has the same intention as module in Verilog, but just in SystemC style.

SC_CTOR

SC_CTOR is macro file for a SystemC contructor. It does several things:

• Declares sensitivty list.

In SystemC a sensitivity list is part of constructor which declares which signals are most sensitive. For example:

sensitive << clk.pos(); 

This tells the module that the design is sensitive to clock, the positive edge in this case.

• Register each function as a process happening in a module.

• Create design hierarchy if you are including serval modules to give whole design sense of module usage.

Threads

Thread is a function made to act like a hardware process. It has a few features:

• Runs concurrently - Multiple processes can be started at the same time(note that every function in systemc is a process)
• They are sensitive to signals.
• They are not called by user, but rather always active.
• There are three types of threads: SC_METHOD, SC_THREAD, SC_CTHREAD.

SC_METHOD

• Limited to single clock cycle. Fine for simple sequential logic
• They execute once every sensiteve event
• They run continuosly
• Are synthesizable
• Are comparable to Verilog's always @ block

SC_THREAD

• Runs once at the start of the simulation, than suspends ifself when done.
• Can conatin infinite loop
• Comparable to Verilog's @ initial block
• Not syntesyzable
• Typicly used in testbecnhes to describe clocks

SC_CTHREAD - clocked threads

• Syntesyzable
• Not limited to one cycle
• Can contain continuous loops
• Can contain large blocks of code for control or code with operations
• Used for behavioral syntesis
• Run continuously
• Can take more clock cycles to execute a single iteration
• Used for 99% of SystemC designs
• Similar to Verilog's always @ (pos/negedge clock)