darkriscv

/*
 * Copyright (c) 2018, Marcelo Samsoniuk
 * 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 holder 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 HOLDER 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.
 */

`timescale 1ns / 1ps
`include "../rtl/config.vh"

module darkcache
#(
    parameter ID = 0
)
(
    input           CLK,    // clock
    input           RES,    // reset
    input           HLT,

    // darkriscv

    input           DDREQ,  // address valid
    input           DRD,    // read/write
    input           DWR,    // read/write
    input   [3:0]   DBE,    // data byte enable
    input   [31:0]  DADDR,  // address
    input   [31:0]  DATAI,  // data input
    output  [31:0]  DATAO,  // data output
    output          DDACK,  // data ack

    output  [31:0]  DATAP, // pipelined data output
    output          DDACKP, // pipelined ack  output
    
    // memory
    
    output          XDREQ,    // address valid
    output          XRD,    // data read
    output          XWR,    // data write
    output [3:0]    XBE,    // byte enable
    output [31:0]   XADDR,  // address
    output [31:0]   XATAO,  // data output
    input  [31:0]   XATAI,  // data input
    input           XDACK,   // data ack

    output  [3:0]   DEBUG   // osciloscope
);

    // cache

`ifdef __CDEPTH__

    wire [31:0] CDATO; 
    
    reg  [31:`__CDEPTH__+2] CTAG   [0:2**`__CDEPTH__-1];    
    reg  [31:0]             CDATA  [0:2**`__CDEPTH__-1];
    reg                     CVAL   [0:2**`__CDEPTH__-1];
    
    integer i;
    
    initial
    begin
`ifdef SIMULATION
        $display("cache%0d: %0dx32-bits (%0d bytes)",
            ID,
            (2**`__CDEPTH__),
            4*(2**`__CDEPTH__));
`endif            
        for(i=0;i!=2**`__CDEPTH__;i=i+1) 
        begin            
            CDATA [i] = 0;
            CTAG  [i] = 0;
            CVAL  [i] = 0;
        end
    end

    wire [`__CDEPTH__-1:0]  CINDEX = DADDR[`__CDEPTH__+1:2];

    wire HIT = RES ? 0 : (DRD && CVAL[CINDEX] && CTAG[CINDEX]==DADDR[31:`__CDEPTH__+2]);
    wire CLR = RES ? 0 : (DWR && CVAL[CINDEX] && CTAG[CINDEX]==DADDR[31:`__CDEPTH__+2]);

    wire DTREQ = RES||HIT ? 0 : (DADDR[31:30]==0||DADDR[31:30]==2) && DRD;

    reg [31:0] DATAOFF = 0;

    always@(posedge CLK)
    begin
        if(DTREQ && XDACK)
        begin
            //$display("cache%0d: miss_on_rd %x:%x\n",ID,DADDR,XATAI);
            CDATA [CINDEX]  <= XATAI;
            CTAG  [CINDEX]  <= DADDR[31:`__CDEPTH__+2];
            CVAL  [CINDEX]  <= 1;
        end
        else
        if(CLR)
        begin
            if(DBE==4'b1111)
            begin
                //$display("cache%0d: miss_on_wr %x:%x\n",ID,DADDR,DATAI);
                CDATA [CINDEX]  <= DATAI;
                CTAG  [CINDEX]  <= DADDR[31:`__CDEPTH__+2];
                CVAL  [CINDEX]  <= 1;   
            end
            else
            begin
                //$display("cache%0d: flush_on_wr %x:%x\n",ID,DADDR,DATAI);
                CVAL  [CINDEX]  <= 0;
            end
        end

        // if(HIT) $display("cache%0d: hit_on_rd %x:%x\n",ID,DADDR,DATAI);

        if(!HLT) DATAOFF <= CDATO;
    end

    assign CDATO  = HIT ? CDATA[CINDEX] : XATAI;        
    assign DATAP  = DATAOFF;   
    
    assign DDACK = HIT ? 1 : XDACK;

    // pipelined output

    reg [31:0] XATAI2  = 0;
   
    reg HIT2   = 0;
    reg XDACK2 = 0;

    wire [31:0] CDATOP;

    always@(posedge CLK)
    begin
        // DATAOFF <= CDATA[CINDEX];
        XATAI2  <= XATAI;
        XDACK2  <= XDACK;
        HIT2    <= HIT;
    end

    assign CDATOP = HIT2 ? DATAOFF       : XATAI2;
    assign DDACKP = HIT ? 0 : HIT2 ? 1 : XDACK2;

`else

    wire [31:0] CDATO = XATAI;
    wire        HIT   = 0;

    assign DDACK = XDACK;

`endif

    // convert darkriscv bus to xbus

    assign XDREQ = HIT ? 0 : DDREQ;
    assign XRD   = HIT ? 0 : DRD;
    assign XWR   = HIT ? 0 : DWR;

    assign XADDR = HIT ? 0 : DADDR;

    assign XBE   = DBE;
    
    assign XATAO = DATAI;
    assign DATAO = CDATO;
    
    assign DEBUG = { DDREQ, HIT, XDREQ, XDACK };

endmodule