Subversion Repositories theia_gpu

`timescale 1ns / 1ps

`include "aDefinitions.v"

/**********************************************************************************

Theia, Ray Cast Programable graphic Processing Unit.

Copyright (C) 2010  Diego Valverde (diego.valverde.g@gmail.com)

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

modify it under the terms of the GNU General Public License

as published by the Free Software Foundation; either version 2

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 General Public License for more details.

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

along with this program; if not, write to the Free Software

Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

***********************************************************************************/

module InstructionDecode

(

input wire                                                                                      Clock,

input wire                                                                                      Reset,

input wire                                                                                      iInstructionAvailable,

input   wire[`INSTRUCTION_WIDTH-1:0]                     iEncodedInstruction,

input   wire[`DATA_ROW_WIDTH-1:0]                                iRamValue0,

input   wire[`DATA_ROW_WIDTH-1:0]                                iRamValue1,

output  wire[`DATA_ADDRESS_WIDTH-1:0]            oRamAddress0,oRamAddress1,

output  wire[`INSTRUCTION_OP_LENGTH-1:0] oOperation,

output  wire [`DATA_ROW_WIDTH-1:0]                       oSource0,oSource1,

output  wire [`DATA_ADDRESS_WIDTH-1:0]      oDestination,

input wire [`DATA_ROW_WIDTH-1:0]          iDataForward,

input wire [`DATA_ADDRESS_WIDTH-1:0]      iLastDestination,

`ifdef DEBUG

        input wire [`ROM_ADDRESS_WIDTH-1:0] iDebug_CurrentIP,

        output wire [`ROM_ADDRESS_WIDTH-1:0] oDebug_CurrentIP,

`endif

output wire                               oDataReadyForExe

);

wire wInmediateOperand;

wire [`DATA_ROW_WIDTH-1:0]       wSource0,wSource1;

wire wTriggerSource0DataForward,wTriggerSource1DataForward;

wire wSource0AddrssEqualsLastDestination,wSource1AddrssEqualsLastDestination;

`ifdef DEBUG

assign oDebug_CurrentIP = iDebug_CurrentIP;

`endif

//See if operation takes scalar argument

assign wInmediateOperand = iEncodedInstruction[`INSTRUCTION_IMM_BITPOS];

//Has the value of the first argument fetched from IMEM

assign wSource0 = iRamValue0;

//Has the value of the second argument fetched from IMEM, or the value of the

//destinatin register in case of scalar operation

assign wSource1 = ( wInmediateOperand ) ? {oRamAddress1,iEncodedInstruction[15:0] ,32'b0,32'b0} : iRamValue1; //{oRamAddress1,oRamAddress0,32'b0,32'b0} : iRamValue1;

//Data forwarding logic

assign wSource0AddrssEqualsLastDestination = (oRamAddress0 == iLastDestination) ? 1'b1: 1'b0;

assign wSource1AddrssEqualsLastDestination = (oRamAddress1 == iLastDestination) ? 1'b1: 1'b0;

assign wTriggerSource0DataForward = wSource0AddrssEqualsLastDestination;

assign wTriggerSource1DataForward = wSource1AddrssEqualsLastDestination && !wInmediateOperand;

//The data address to fetch from IMEM

assign oRamAddress1 = iEncodedInstruction[31:16];

//If operation takes a scalar value, then ask IMEM

//for the previous value of the destination ([47:32])

//and have this value ready at oRamAddress0

MUXFULLPARALELL_16bits_2SEL RAMAddr0MUX

 (

  .Sel( wInmediateOperand ),

  .I1( iEncodedInstruction[15:0] ),

  .I2( iEncodedInstruction[47:32] ),

  .O1( oRamAddress0 )

 );

//One clock cycle after the new instruction becomes

//available to IDU, it should be decoded and ready 

//for execution

FFD_POSEDGE_SYNCRONOUS_RESET # ( 1 ) FFD1

(

        .Clock( Clock ),

        .Reset( Reset ),

        .Enable(1'b1),

        .D( iInstructionAvailable ),

        .Q( oDataReadyForExe )

);

//Latch the Operation

FFD_POSEDGE_SYNCRONOUS_RESET # ( `INSTRUCTION_OP_LENGTH ) FFD3

(

        .Clock(Clock),

        .Reset(Reset),

        .Enable(iInstructionAvailable),

        .D(iEncodedInstruction[`INSTRUCTION_WIDTH-1:`INSTRUCTION_WIDTH-`INSTRUCTION_OP_LENGTH]),

        .Q(oOperation )

);

//Latch the Destination

FFD_POSEDGE_SYNCRONOUS_RESET # ( `DATA_ADDRESS_WIDTH ) FFD2

(

        .Clock(Clock),

        .Reset(Reset),

        .Enable(iInstructionAvailable),

        .D(iEncodedInstruction[47:32]),

        .Q(oDestination )

);

//Once we made a decicions if the Sources must be forwarded or not, a series of muxes

//are used to routed the correct data into the decoded Source outputs

MUXFULLPARALELL_96bits_2SEL Source0_Mux

(

        .Sel( wTriggerSource0DataForward ),

        .I1( wSource0  ),

        .I2( iDataForward ),

        .O1( oSource0 )

);

MUXFULLPARALELL_96bits_2SEL Source1_Mux

(

        .Sel( wTriggerSource1DataForward ),

        .I1( wSource1  ),

        .I2( iDataForward ),

        .O1( oSource1 )

);

endmodule