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// ----------------------------------------------------------------------------

// Debug Unit memory cache: definition

// Copyright (C) 2008  Embecosm Limited <info@embecosm.com>

// Contributor Jeremy Bennett <jeremy.bennett@embecosm.com>

// This file is part of the GDB interface to the cycle accurate model of the

// OpenRISC 1000 based system-on-chip, ORPSoC, built using Verilator.

// This program is free software: you can redistribute it and/or modify it

// under the terms of the GNU Lesser General Public License as published by

// the Free Software Foundation, either version 3 of the License, or (at your

// option) any later version.

// This program is distributed in the hope that it will be useful, but WITHOUT

// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public

// License for more details.

// You should have received a copy of the GNU Lesser General Public License

// along with this program.  If not, see <http://www.gnu.org/licenses/>.

// ----------------------------------------------------------------------------

// $Id: MemCache.h 326 2009-03-07 16:47:31Z jeremy $

#ifndef MEM_CACHE__H

#define MEM_CACHE__H

#include <stdint.h>

//! Module for cacheing memory accesses by the debug unit

//! Memory reads and writes through the Debug Unit via JTAG are time

//! consuming - of the order of 1000 CPU clock cycles. However when the

//! processor is stalled the values cannot change, other than through the

//! debug unit, so it makes sense to cache values.

//! Cacheing the entire memory is too much (it does need to be cleared when

//! the processor is unstalled. This class provides a cacheing function using

//! a closed hash table.

//! In the event of a clash on write, the old value is replaced by the new

//! value.

class MemCache

{

public:

  // Constructor and destructor

  MemCache (int  _tableSize = 1009);

  ~MemCache ();

  // Functions

  void  clear ();

  void  write (uint32_t  addr,

               uint32_t  value);

  bool  read (uint32_t  addr,

              uint32_t &value);

private:

  //! The size of the hash table. A prime number is a good choice.

  int  tableSize;

  // The hash table, keyed by address. Done as three parallel vectors,

  // allowing unambiguous clearing by use of memset for efficiency.

  bool     *tabIsValid;

  uint32_t *tabKeyAddr;

  uint32_t *tabValue;

};      // MemCache ()

#endif  // MEM_CACHE__H