Subversion Repositories m65c02

////////////////////////////////////////////////////////////////////////////////

//

//  Copyright 2013 by Michael A. Morris, dba M. A. Morris & Associates

//

//  All rights reserved. The source code contained herein is publicly released

//  under the terms and conditions of the GNU Lesser Public License. No part of

//  this source code may be reproduced or transmitted in any form or by any

//  means, electronic or mechanical, including photocopying, recording, or any

//  information storage and retrieval system in violation of the license under

//  which the source code is released.

//

//  The source code contained herein is free; it may be redistributed and/or

//  modified in accordance with the terms of the GNU Lesser General Public

//  License as published by the Free Software Foundation; either version 2.1 of

//  the GNU Lesser General Public License, or any later version.

//

//  The source code contained herein is freely released WITHOUT ANY WARRANTY;

//  without even the implied warranty of MERCHANTABILITY or FITNESS FOR A

//  PARTICULAR PURPOSE. (Refer to the GNU Lesser General Public License for

//  more details.)

//

//  A copy of the GNU Lesser General Public License should have been received

//  along with the source code contained herein; if not, a copy can be obtained

//  by writing to:

//

//  Free Software Foundation, Inc.

//  51 Franklin Street, Fifth Floor

//  Boston, MA  02110-1301 USA

//

//  Further, no use of this source code is permitted in any form or means

//  without inclusion of this banner prominently in any derived works.

//

//  Michael A. Morris

//  Huntsville, AL

//

////////////////////////////////////////////////////////////////////////////////

`timescale 1ns / 1ps

////////////////////////////////////////////////////////////////////////////////

// Company:         M. A. Morris & Associates 

// Engineer:        Michael A. Morris 

// 

// Create Date:     12:06:18 08/18/2013 

// Design Name:     M65C02 -  

// Module Name:     M65C02_IntHndlr.v 

// Project Name:    C:\XProjects\ISE10.1i\M65C02 

// Target Devices:  SRAM-based FPGAs: XC3S50A-xVQ100I, XC3S200A-xVQ100I 

// Tool versions:   Xilinx ISE 10.1i SP3

// 

// Description: 

//

//  This module implements a simple interrupt handler for the M65C02 soft-core

//  microprocessor. It accepts external active low inputs for Non-Maskable

//  Interrupt request (nNMI) and maskable Interrupt ReQuest (nIRQ). It synchro-

//  nizes both inputs to the internal system clock (Clk), and generates internal

//  signals NMI and IRQ. NMI is falling edge sensitive, and IRQ is active low

//  level sensitive. The module also accepts the core's mode output (Mode) and

//  generates an internal BReaK software trap request (BRK).

//

//  The non-maskable interrupt request, nNMI, has priority, followed by BRK, and

//  finally nIRQ. The core, from the I bit in the processor register, provides a

//  mask that prevents the generation of the internal IRQ signal.

//

//  Vectors for each of the four interrupt/trap sources are set using para-

//  meters. The current implementation aims to maintain compatibility with the

//  WDC W65C02S processor, so IRQ and BRK share the same vector. A quick edit

//  of the parameters allows an independent vector location to be added for BRK.

//  Similarly, the vectors for any of the interrupt/trap sources can be moved

//  to any location in the memory space, if W65C02S compatibility is not desired

//  or required.

//

// Dependencies:    fedet.v 

//

// Revision:

//

//  0.01    13H18   MAM     File Created 

// 

// Additional Comments: 

//

///////////////////////////////////////////////////////////////////////////////

module M65C02_IntHndlr #(

    parameter pIRQ_Vector = 16'hFFFE,

    parameter pBRK_Vector = 16'hFFFE,

    parameter pRST_Vector = 16'hFFFC,

    parameter pNMI_Vector = 16'hFFFA,

    parameter pBRK        = 3'b010

)(

    input   Rst,

    input   Clk,

    input   nNMI,

    input   nIRQ,

    input   [2:0] Mode,

    input   IRQ_Msk,

    input   IntSvc,

    output  reg Int,

    output  reg [15:0] Vector,

    output  reg NMI,

    output  reg IRQ,

    output  reg Brk

);

////////////////////////////////////////////////////////////////////////////////

//

//  Local Declarations

//

wire    RE_NMI;

wire    CE_NMI;

reg     nIRQ_IFD;

//  Perform falling edge detection on the external non-maskable interrupt input

fedet   FE3 (

            .rst(Rst),

            .clk(Clk),

            .din(nNMI),

            .pls(RE_NMI)

        );

//  Capture and hold the rising edge pulse for NMI in NMI FF until serviced by

//      the processor.

assign CE_NMI = (Rst | IntSvc | RE_NMI);

always @(posedge Clk) NMI <= #1 ((CE_NMI) ? RE_NMI : 0);

//  Synchronize external IRQ input to Clk

always @(posedge Clk or posedge Rst)

begin

    if(Rst) begin

        nIRQ_IFD <= #1 1;

        IRQ      <= #1 0;

    end else begin

        nIRQ_IFD <= #1 nIRQ;

        IRQ      <= #1 ~nIRQ_IFD;

    end

end

//assign Brk    = (Mode == pBRK);

//assign Int    = (NMI | (~IRQ_Msk & IRQ));

//

//always @(*) Vector = ((Int) ? ((NMI) ? pNMI_Vector

//                                     : pIRQ_Vector)

//                            : ((Brk) ? pBRK_Vector

//                                     : pRST_Vector));

always @(posedge Clk or posedge Rst)

begin

    if(Rst) begin

        Brk    <= #1 0;

        Int    <= #1 0;

        Vector <= #1 pRST_Vector;

    end else begin

        Brk    <= #1 (Mode == pBRK);

        Int    <= #1 (NMI | (~IRQ_Msk & IRQ));

        Vector <= #1 ((Int) ? ((NMI) ? pNMI_Vector

                                     : pIRQ_Vector)

                            : ((Brk) ? pBRK_Vector

                                     : pRST_Vector));

    end

end

endmodule