File: M6507Lo.hxx

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//============================================================================
//
//    SSSS    tt          lll  lll              
//   SS  SS   tt           ll   ll                
//   SS     tttttt  eeee   ll   ll   aaaa    "An Atari 2600 VCS Emulator"
//    SSSS    tt   ee  ee  ll   ll      aa      
//       SS   tt   eeeeee  ll   ll   aaaaa   Copyright (c) 1995,1996,1997
//   SS  SS   tt   ee      ll   ll  aa  aa         Bradford W. Mott
//    SSSS     ttt  eeeee llll llll  aaaaa    
//
//============================================================================

#ifndef M6507LOW_HXX
#define M6507LOW_HXX

#include <fstream.h>

class M6507Low;

#include "machine.hxx"
#include "System.hxx"
#include "M6507.hxx"

/**
  This class emulates a 6507 microprocessor, however, the memory 
  accesses and cycle counts it generates are only valid at the 
  instruction level.  For better compatibility it's neccessary to 
  increment cycles counts at the sub-instruction level and issues 
  "false" reads for some instructions (such as Indirect,X addressing 
  when it crosses a page boundary).
  
  @author  Bradford W. Mott
  @version $Id: M6507Lo.hxx,v 1.1 1997/05/17 19:04:13 bwmott Exp $
*/
class M6507Low : public M6507
{
  public:
    /// Constructor
    M6507Low(System& system);

    /// Destructor
    virtual ~M6507Low();

  public:
    /**
      Execute instructions until at least the given number of 
      cycles have passed or execution is halted by someone
    */
    virtual void execute(uLong numberOfCycles);

  private:
    // Answer the uByte at the given address (only lower 8-bits used)
    uWord peek(uWord addr);

    // Answer the uByte at the given address that should be part of
    // an instruction we're trying to execute
    uWord iPeek(uWord addr);

    // Answer the uWord at the given address that should be part of
    // an instruction we're trying to execute
    uWord iDPeek(uWord addr);

    // Write value at the given address.
    void poke(uWord addr, uByte value);
};
#endif