simple_bus_arbiter.cpp

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/*****************************************************************************
 
  simple_bus_arbiter.cpp : The arbitration unit.
 
  Original Author: Ric Hilderink, Synopsys, Inc., 2001-10-11
 
 *****************************************************************************/
 
/*****************************************************************************
 
  MODIFICATION LOG - modifiers, enter your name, affiliation, date and
  changes you are making here.
 
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  Description of Modification:
 
 *****************************************************************************/

#include "simple_bus_arbiter.h"

simple_bus_request *
simple_bus_arbiter::arbitrate(const simple_bus_request_vec &requests)
{
  unsigned int i;
  // at least one request is here
  simple_bus_request *best_request = requests[0]; 

  if (m_verbose) 
    { // shows the list of pending requests
      sb_fprintf(stdout, "%s %s :", sc_time_stamp().to_string().c_str(), name());
      for (i = 0; i < requests.size(); ++i)
	{
	  simple_bus_request *request = requests[i];
          // simple_bus_lock_status encoding
          const char lock_chars[] = { '-', '=', '+' };
          // simple_bus_status encoding
           sb_fprintf(stdout, "\n    R[%d](%c%s@%x)",
                     request->priority,
                     lock_chars[request->lock],
                     simple_bus_status_str[request->status],
                     request->address);
	}
    }

  // highest priority: status==SIMPLE_BUS_WAIT and lock is set: 
  // locked burst-action
  for (i = 0; i < requests.size(); ++i)
    {
      simple_bus_request *request = requests[i];
      if ((request->status == SIMPLE_BUS_WAIT) &&
	  (request->lock == SIMPLE_BUS_LOCK_SET))
	{
	  // cannot break-in a locked burst
	  if (m_verbose)
            sb_fprintf(stdout, " -> R[%d] (rule 1)\n", request->priority);
	  return request;
	}
    }

  // second priority: lock is set at previous call, 
  // i.e. SIMPLE_BUS_LOCK_GRANTED
  for (i = 0; i < requests.size(); ++i)
    if (requests[i]->lock == SIMPLE_BUS_LOCK_GRANTED)
      {
	if (m_verbose)
	  sb_fprintf(stdout, " -> R[%d] (rule 2)\n", requests[i]->priority);
	return requests[i];
      }

  // third priority: priority
  for (i = 1; i < requests.size(); ++i)
    {
      sc_assert(requests[i]->priority != best_request->priority);
      if (requests[i]->priority < best_request->priority)
	best_request = requests[i];
    }

  if (best_request->lock != SIMPLE_BUS_LOCK_NO)
    best_request->lock = SIMPLE_BUS_LOCK_GRANTED;
	
  if (m_verbose) 
    sb_fprintf(stdout, " -> R[%d] (rule 3)\n", best_request->priority);

  return best_request;
}