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SOLVED: Nevermind, I made some mistakes in calling the wrong methods for writing/reading from ports. Thanks for your attention anyway! I'm trying to implement this example of a memory and a cpu that are communicating. CPU <==> MEM The modules use a single bidirectional data-line for reading/writing. I defined a signal in sc_main: sc_signal<int,SC_MANY_WRITERS> s_memdata; which I connect to the CPU and MEM module through their ports: sc_inout<int> p_memdata; The CPU is writing to the s_memdata signal: p_memdata.write(getrnddata()); As well as the memory: p_data.write( m_data[ m_curAddr ] ); In the debugger I see that the m_curAddr is changing correctly. Yet, the VCD file shows that the signal "data" is not changing when the "address" is changed (as shown in the figure) Actually, the "data" only changes when the cpu is writing to it, not when the memory is. (I was not able to show the function read/write signal because the enum didn't show in the VCD file). It seems to me that there is something going on with the two modules writing to the same channel. I've noticed sc_logic that introduces Z and X values, is this the appropriate way? edit: I've created a simple proof of principle with two writers that talk to a single sc_signal< bool, SC_MANY_WRITERS > which seems to work. So the problem is something different. Thanks for any help or tips. mem_tb.cpp int sc_main(int argc, char* args[]){ Memory * mem; CPU * cpu; mem = new Memory("main_memory"); cpu = new CPU("cpu"); /* sgn */ sc_signal<Memory::Function,SC_MANY_WRITERS> s_memfunc; sc_signal<Memory::RETSignal> s_memsig; sc_signal<int> s_memaddr; sc_signal<int,SC_MANY_WRITERS> s_memdata; sc_clock clk; mem->p_addr(s_memaddr); mem->p_func(s_memfunc); mem->p_data(s_memdata); mem->p_sig(s_memsig); cpu->p_memdata(s_memdata); cpu->p_memaddr(s_memaddr); cpu->p_memsig(s_memsig); cpu->p_memfunc(s_memfunc); mem->clk( clk ); cpu->clk( clk ); std::cout << "Running, CTRL+C to exit..." << std::endl; sc_trace_file * trace = sc_create_vcd_trace_file("trace"); sc_trace(trace, s_memaddr, "addr"); sc_trace(trace, s_memdata, "data"); sc_trace(trace, s_memfunc, "func"); sc_trace(trace, s_memsig, "sig"); sc_start(); sc_close_vcd_trace_file( trace ); return 0; } cpu.h #include <systemc.h> #include "memory.h" #include <boost/random.hpp> SC_MODULE( CPU ) { public: sc_in<bool> clk; sc_in<Memory::RETSignal> p_memsig; sc_out<Memory::Function> p_memfunc; sc_out<int> p_memaddr; sc_inout<int> p_memdata; SC_CTOR( CPU ) { SC_METHOD(exec); sensitive << clk.pos(); dont_initialize(); SC_METHOD(done); sensitive << p_memsig; dont_initialize(); m_waitmem = false; rng.seed( time(NULL) ); dist = new boost::random::uniform_int_distribution<>(0,1<<16); } private: boost::random::mt19937 rng; boost::random::uniform_int_distribution<> *dist; bool m_waitmem; int rand(); Memory::Function getrndfunc(); int getrndaddr(); int getrnddata(); void exec(); void done(); }; cpu.cpp Memory::Function CPU::getrndfunc() { switch( rand() % 2 ) { case 0 : { return Memory::FUNC_READ; } default : { return Memory::FUNC_WRITE; } /* 1, and all other cases... */ } } int CPU::getrndaddr() { return rand() % MEM_SIZE; } int CPU::getrnddata() { return rand(); } int CPU::rand() { return (*dist)(rng); } void CPU::exec() { if(m_waitmem) return; int addr = getrndaddr(); Memory::Function f = getrndfunc(); p_memfunc.write(f); p_memaddr.write(addr); if(f==Memory::FUNC_WRITE) p_memdata.write(getrnddata()); } void CPU::done() { if( p_memsig.read() == Memory::RSIG_NONE ) return; m_waitmem = false; p_memfunc.write(Memory::FUNC_NONE); } memory.h #define MEM_SIZE 512 SC_MODULE( Memory ) { public: enum Function { FUNC_NONE = 0, FUNC_READ = 1, FUNC_WRITE = 2 }; enum RETSignal { RSIG_NONE, RSIG_READ_FIN, RSIG_WRITE_FIN, RSIG_ERR }; sc_in<bool> clk; sc_in<Function> p_func; sc_in<int> p_addr; sc_inout<int> p_data; sc_out<RETSignal> p_sig; SC_CTOR( Memory ){ SC_METHOD(execute); sensitive << clk.neg(); m_clkCnt = 0; m_curAddr = 0; m_curData = 0; m_curFunc = Memory::FUNC_NONE; m_data = new int[MEM_SIZE]; m_writesCnt = 0; m_readsCnt = 0; m_errorsCnt = 0; m_errorCode = 0; } ~Memory(); private: int m_clkCnt; int m_curAddr; int m_curData; Function m_curFunc; int* m_data; int m_errorCode; int m_writesCnt; int m_readsCnt; int m_errorsCnt; RETSignal read(); RETSignal write(); void execute(); }; memory.cpp #include "memory.h" Memory::~Memory() { delete[] m_data; } Memory::RETSignal Memory::read() { if( m_errorCode ) { m_errorsCnt++; return RSIG_ERR; } p_data.write( m_data[ m_curAddr ] ); m_readsCnt++; return RSIG_READ_FIN; } Memory::RETSignal Memory::write() { if( m_errorCode ) { m_errorsCnt++; return RSIG_ERR; } m_data[ m_curAddr ] = m_curData; m_writesCnt++; return RSIG_WRITE_FIN; } void Memory::execute() { if( m_curFunc != FUNC_NONE ) { m_clkCnt++; if( m_clkCnt == 100 ) { RETSignal retSig = RSIG_ERR; switch(m_curFunc){ case FUNC_READ : { retSig = read(); break; } case FUNC_WRITE : { retSig = write(); break; } default : { /* */ } } p_sig.write( retSig ); m_clkCnt = 0; m_curFunc = FUNC_NONE; } return; } if( p_func == FUNC_NONE ) return; m_curFunc = p_func.read(); m_curAddr = p_addr.read(); m_curData = p_data.read(); p_sig.write( RSIG_NONE ); }