Problem Halting Execution

I'm writing a SID port, and I can't get it to halt properly.  What is
the functionality of yield()?  It does not seem to stop instruction
flow.  When yield() is called step_insns() will return after the break
at the end of the loop but then it gets called again.  Included is
pseudocode for my step_insns() function.  Any help would be
appreciated.

Thanks!
Joseph Altmaier

void
*processor*_cpu::step_insns ()
{
  bool found;

  while (true)
    {
      get next PC

      for(int u = 0; u < 2; u++) {//Two execution units

        Get next instruction for current execution unit

        if (the instruction is not found)
        {
          Get the instruction manually
        }

        Instruction disassembley...

        try//Execute the instruction and cope with it if the instruction fails.
        {
          Execute the current instruction for the current execution unit
        }
        catch (cpu_memory_fault& t)
        {
          this->memory_trap (t);
          this->yield ();
        }
        catch (cpu_exception& t)
        {
          this->yield ();//A halt instruction will cause a
cpu_exception and a yeild()
        }

        try {
          if(Second execution unit){
            Execute a writeback on a pair of write stacks
          }
        }
        catch (cpu_memory_fault& t)
        {
          this->memory_trap (t);
          this->yield();
        }
        catch (cpu_exception& t)
        {
          this->yield ();
        }

        move ahead through circular pipeline

        Do post-instruction processing
      }

      if (stop_after_insns_p (1))
        break;
    }
}