The class is declared as having a dynamic process, since the constructor will set up a SystemC thread.

SC_HAS_PROCESS (JtagLoggerSC);
	  

The constructor passes the module name up to the base class. It associates the payload extension instance with the generic payload instance. Finally it declares a new SystemC thread.

We must use a SC_THREAD rather than SC_METHOD since the thread method, runJtag will wait () for one second between each read of the next program counter.

  payload.set_extension (&ext);
  SC_THREAD (runJtag);
	  

The main thread method, runJtag uses the various support utilities to construct JTAG registers which are then transported to the target wrapped ISS

First the JTAG reset, instruction and module selection are shifted, each followed by a message, noting how long the step took.

jtagReset (delay);
cout << "Reset after " << delay << "." << endl;
wait (SC_ZERO_TIME);

delay = SC_ZERO_TIME;
jtagInstruction (DEBUG_INST, delay);
cout << "Instruction shifted after " << delay << "." << endl;
wait (SC_ZERO_TIME);

delay = SC_ZERO_TIME;
jtagSelectModule (CPU0_MOD, delay);
cout << "Module selected after " << delay << "." << endl;
wait (SC_ZERO_TIME);
	  

A wait for zero time between each transaction ensures any other thread has an opportunity to resume if needed.

The main loop reads the next program counter, waiting for one second between each loop. The read involves two transactions, one WRITE_COMMAND to specify the transfer required, one GO_COMMAND to accomplish the transfer.

while (true)
  {
    // Specify the WRITE_COMMAND to read the NPC SPR
    delay = SC_ZERO_TIME;
    jtagWriteCommand (READ32, SPR_NPC, 4, delay);
    cout << "WRITE_COMMAND after " << delay << "." << endl;
    wait (SC_ZERO_TIME);

    // Read the data, remembering that OR1200 is big endian
    unsigned char  res[4];            // For the data read back

    delay = SC_ZERO_TIME;
    jtagGoCommandRead (res, 4, delay);
    cout << "GO_COMMAND after " << delay << "." << endl;
    cout << "- NPC = 0x" << hex << (int) res[3] << (int) res[2]
         << (int) res[1] << (int) res[0] << dec << "." << endl;
    wait (sc_time (1000.0, SC_MS));
  }
	  

The utilities to help in constructing registers and passing them to the target are largely concerned with the minutiae of format. In each the register is constructed, transported to the target and the returned register analyzed.

The implementation of the JTAG logger module class, JtagLoggerSC may be found in sys-models/jtag-soc/JtagLoggerSC.cpp in the distribution.