gem5/src/arch/alpha/decoder.hh

/*
 * Copyright (c) 2012 Google
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met: redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer;
 * redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution;
 * neither the name of the copyright holders nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Authors: Gabe Black
 */

#ifndef __ARCH_ALPHA_DECODER_HH__
#define __ARCH_ALPHA_DECODER_HH__

#include "arch/generic/decode_cache.hh"
#include "arch/types.hh"
#include "cpu/static_inst.hh"
#include "sim/full_system.hh"

namespace AlphaISA
{

class ISA;
class Decoder
{
  protected:
    // The extended machine instruction being generated
    ExtMachInst ext_inst;
    bool instDone;

  public:
    Decoder(ISA* isa = nullptr) : instDone(false)
    {}

    void
    process()
    { }

    void
    reset()
    {
        instDone = false;
    }

    // Use this to give data to the predecoder. This should be used
    // when there is control flow.
    void
    moreBytes(const PCState &pc, Addr fetchPC, MachInst inst)
    {
        ext_inst = inst;
        instDone = true;
        if (FullSystem)
            ext_inst |= (static_cast<ExtMachInst>(pc.pc() & 0x1) << 32);
    }

    bool
    needMoreBytes()
    {
        return true;
    }

    bool
    instReady()
    {
        return instDone;
    }

    void takeOverFrom(Decoder * old) {}

  protected:
    /// A cache of decoded instruction objects.
    static GenericISA::BasicDecodeCache defaultCache;

  public:
    StaticInstPtr decodeInst(ExtMachInst mach_inst);

    /// Decode a machine instruction.
    /// @param mach_inst The binary instruction to decode.
    /// @retval A pointer to the corresponding StaticInst object.
    StaticInstPtr
    decode(ExtMachInst mach_inst, Addr addr)
    {
        return defaultCache.decode(this, mach_inst, addr);
    }

    StaticInstPtr
    decode(AlphaISA::PCState &nextPC)
    {
        if (!instDone)
            return NULL;
        instDone = false;
        return decode(ext_inst, nextPC.instAddr());
    }
};

} // namespace AlphaISA

#endif // __ARCH_ALPHA_DECODER_HH__