//=============================================================================
//
//      openrisc_opcode.h
//
//  Define the instruction formats and opcode values for the OpenRISC
//  instruction set...or at least just enough of them to implement
//  single-stepping.
//
//=============================================================================
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//
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//=============================================================================
//#####DESCRIPTIONBEGIN####
//
// Author(s):   sfurman
// Contributors:
// Date:        2003-02-28
// Purpose:     Allow dissection of OpenRISC instructions
// Description: The types and macros defined here define the instruction
//              formats of the OpenRISC instruction set...or at least the
//              very limited subset necessary to allow single-stepping.
//              
//####DESCRIPTIONEND####
//
//=============================================================================

#ifndef _OPENRISC_OPCODE_H
#define _OPENRISC_OPCODE_H


// Define the instruction formats.
typedef union {
    unsigned word;

    // (Possibly conditional) relative jump w/ immediate displacement
    struct {
        unsigned op:      6;    // OP_J, OP_JAL, OP_BNF, or OP_BF
        signed   target: 26;
    } JType;

    // Absolute jump w/ register contents used as PC target address
    struct {
        unsigned op:      6;	// OP_JR or OP_JALR
        unsigned unused1:10;
        unsigned rB:      5;	// Register containing new PC
        unsigned unused2:11;
    } JRType;

} InstFmt;

/*
 * Values for the 'op' field.
 */
#define OP_J            0x00
#define OP_JAL          0x01
#define OP_BNF          0x03
#define OP_BF           0x04
#define OP_RFE          0x09
#define OP_JR           0x11
#define OP_JALR         0x12

#endif  /* _OPENRISC_OPCODE_H */

// EOF openrisc_opcode.h
