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

//                                                              //

//  L1 Cache for Amber 2 Core                                   //

//                                                              //

//  This file is part of the Amber project                      //

//  http://www.opencores.org/project,amber                      //

//                                                              //

//  Description                                                 //

//  Synthesizable L1 Unified Data and Instruction Cache         //

//  Cache is 4-way, 256 line and 16 bytes per line for          //

//  a total of 16KB. The cache policy is write-through and      //

//  read allocate. For swap instructions (SWP and SWPB) the     //

//  location is evicted from the cache and read from main       //

//  memory.                                                     //

//                                                              //

//  Author(s):                                                  //

//      - Conor Santifort, csantifort.amber@gmail.com           //

//                                                              //

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

//                                                              //

// Copyright (C) 2010 Authors and OPENCORES.ORG                 //

//                                                              //

// This source file may be used and distributed without         //

// restriction provided that this copyright statement is not    //

// removed from the file and that any derivative work contains  //

// the original copyright notice and the associated disclaimer. //

//                                                              //

// This source file is free software; you can redistribute it   //

// and/or modify it under the terms of the GNU Lesser General   //

// Public License as published by the Free Software Foundation; //

// either version 2.1 of the License, or (at your option) any   //

// later version.                                               //

//                                                              //

// This source 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 Lesser General Public License for more //

// details.                                                     //

//                                                              //

// You should have received a copy of the GNU Lesser General    //

// Public License along with this source; if not, download it   //

// from http://www.opencores.org/lgpl.shtml                     //

//                                                              //

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

`include "global_defines.v"

`include "a23_config_defines.v"

module a23_cache

#(

// ---------------------------------------------------------

// Cache Configuration

// Limited to Linux 4k page sizes -> 256 lines

parameter CACHE_LINES          = 256,

// This cannot be changed without some major surgeory on

// this module                                       

parameter CACHE_WORDS_PER_LINE = 4,

// Changing this parameter is the recommended

// way to change the overall cache size; 2, 4 and 8 ways are supported.

//   2 ways -> 8KB  cache

//   4 ways -> 16KB cache

//   8 ways -> 32KB cache

parameter WAYS              = `A23_CACHE_WAYS ,

// derived configuration parameters

parameter CACHE_ADDR_WIDTH  = log2 ( CACHE_LINES ),                        // = 8

parameter WORD_SEL_WIDTH    = log2 ( CACHE_WORDS_PER_LINE ),               // = 2

parameter TAG_ADDR_WIDTH    = 32 - CACHE_ADDR_WIDTH - WORD_SEL_WIDTH - 2,  // = 20

parameter TAG_WIDTH         = TAG_ADDR_WIDTH + 1,                          // = 21, including Valid flag

parameter CACHE_LINE_WIDTH  = CACHE_WORDS_PER_LINE * 32,                   // = 128

parameter TAG_ADDR32_LSB    = CACHE_ADDR_WIDTH + WORD_SEL_WIDTH + 2,       // = 12

parameter CACHE_ADDR32_MSB  = CACHE_ADDR_WIDTH + WORD_SEL_WIDTH + 2 - 1,   // = 11

parameter CACHE_ADDR32_LSB  =                    WORD_SEL_WIDTH + 2    ,   // = 4

parameter WORD_SEL_MSB      = WORD_SEL_WIDTH + 2 - 1,                      // = 3

parameter WORD_SEL_LSB      =                  2                           // = 2

// ---------------------------------------------------------

)

(

input                               i_clk,

// Read / Write requests from core

input                               i_select,

input                               i_exclusive,        // exclusive access, part of swap instruction

input      [31:0]                   i_write_data,

input                               i_write_enable,     // core issued write request

input      [31:0]                   i_address,          // registered address from execute

input      [31:0]                   i_address_nxt,      // un-registered version of address from execute stage

input      [3:0]                    i_byte_enable,

input                               i_cache_enable,     // from co-processor 15 configuration register

input                               i_cache_flush,      // from co-processor 15 register

output      [31:0]                  o_read_data,

input                               i_core_stall,

output                              o_stall,

// WB Read Request                                                          

output                              o_wb_req,          // Read Request

input      [31:0]                   i_wb_address,      // wb bus                                 

input      [31:0]                   i_wb_read_data,    // wb bus                              

input                               i_wb_stall         // wb_stb && !wb_ack

);

`include "a23_localparams.v"

`include "a23_functions.v"

// One-hot encoded

localparam       C_INIT   = 0,

                 C_CORE   = 1,

                 C_FILL   = 2,

                 C_INVA   = 3,

                 C_STATES = 4;

localparam [3:0] CS_INIT            = 4'd0,

                 CS_IDLE            = 4'd1,

                 CS_FILL1           = 4'd2,

                 CS_FILL2           = 4'd3,

                 CS_FILL3           = 4'd4,

                 CS_FILL4           = 4'd5,

                 CS_FILL_COMPLETE   = 4'd6,

                 CS_TURN_AROUND     = 4'd7,

                 CS_WRITE_HIT1      = 4'd8,

                 CS_EX_DELETE       = 4'd9;

reg  [3:0]                  c_state    = CS_IDLE;

reg  [C_STATES-1:0]         source_sel = 1'd1 << C_CORE;

reg  [CACHE_ADDR_WIDTH:0]   init_count = 'd0;

wire [TAG_WIDTH-1:0]        tag_rdata_way [WAYS-1:0];

wire [CACHE_LINE_WIDTH-1:0] data_rdata_way[WAYS-1:0];

wire [WAYS-1:0]             data_wenable_way;

wire [WAYS-1:0]             data_hit_way;

wire [WAYS-1:0]             tag_wenable_way;

reg  [WAYS-1:0]             select_way = 'd0;

wire [WAYS-1:0]             next_way;

reg  [WAYS-1:0]             valid_bits_r = 'd0;

reg  [3:0]                  random_num = 4'hf;

wire [CACHE_ADDR_WIDTH-1:0] tag_address;

wire [TAG_WIDTH-1:0]        tag_wdata;

wire                        tag_wenable;

wire [CACHE_LINE_WIDTH-1:0] read_miss_wdata;

wire [CACHE_LINE_WIDTH-1:0] write_hit_wdata;

wire [CACHE_LINE_WIDTH-1:0] data_wdata;

wire [CACHE_ADDR_WIDTH-1:0] data_address;

wire [31:0]                 write_data_word;

wire                        hit;

wire                        read_miss;

wire                        write_miss;

wire                        write_hit;

reg  [31:0]                 miss_address = 'd0;

wire [CACHE_LINE_WIDTH-1:0] hit_rdata;

wire                        write_stall;

wire                        cache_busy_stall;

wire                        read_stall;

wire                        enable;

wire [CACHE_ADDR_WIDTH-1:0] address;

reg  [CACHE_LINE_WIDTH-1:0] wb_rdata_burst = 'd0;

reg                         wb_read_buf_valid = 'd0;

reg  [31:0]                 wb_read_buf_address = 'd0;

reg  [31:0]                 wb_read_buf_data = 'd0;

wire                        wb_read_buf_hit;

wire                        exclusive_access;

wire                        ex_read_hit;

reg                         ex_read_hit_r = 'd0;

reg  [WAYS-1:0]             ex_read_hit_way = 'd0;

reg  [CACHE_ADDR_WIDTH-1:0] ex_read_address;

wire                        ex_read_hit_clear;

wire                        ex_read_cache_busy;

genvar                      i;

// ======================================

// Address to use for cache access

// ======================================

// If currently stalled then the address for the next

// cycle will be the same as it is in the current cycle

//

assign address = i_core_stall ? i_address    [CACHE_ADDR32_MSB:CACHE_ADDR32_LSB] :

                                i_address_nxt[CACHE_ADDR32_MSB:CACHE_ADDR32_LSB] ;

// ======================================

// Outputs

// ======================================

assign o_read_data      = wb_read_buf_hit                              ? wb_read_buf_data   :

                          i_address[WORD_SEL_MSB:WORD_SEL_LSB] == 2'd0 ? hit_rdata [31:0]   :

                          i_address[WORD_SEL_MSB:WORD_SEL_LSB] == 2'd1 ? hit_rdata [63:32]  :

                          i_address[WORD_SEL_MSB:WORD_SEL_LSB] == 2'd2 ? hit_rdata [95:64]  :

                                                                         hit_rdata [127:96] ;

// Don't allow the cache to stall the wb i/f for an exclusive access

// The cache needs a couple of cycles to flush a potential copy of the exclusive

// address, but the wb can do the access in parallel. So there is no

// stall in the state CS_EX_DELETE, even though the cache is out of action. 

// This works fine as long as the wb is stalling the core

assign o_stall          = read_stall || write_stall || cache_busy_stall || ex_read_cache_busy;

assign o_wb_req        = (( read_miss || write_miss ) && c_state == CS_IDLE ) ||

                          c_state == CS_WRITE_HIT1;

// ======================================

// Cache State Machine

// ======================================

// Little State Machine to Flush Tag RAMS

always @ ( posedge i_clk )

    if ( i_cache_flush )

        begin

        c_state     <= C_INIT;

        source_sel  <= 1'd1 << C_INIT;

        init_count  <= 'd0;

        `ifdef A23_CACHE_DEBUG

        `TB_DEBUG_MESSAGE

        $display("Cache Flush");

        `endif

        end

    else

        case ( c_state )

            CS_INIT :

                if ( init_count < CACHE_LINES [CACHE_ADDR_WIDTH:0] )

                    begin

                    init_count  <= init_count + 1'd1;

                    source_sel  <= 1'd1 << C_INIT;

                    end

                else

                    begin

                    source_sel  <= 1'd1 << C_CORE;

                    c_state     <= CS_TURN_AROUND;

                    end

             CS_IDLE :

                begin

                source_sel  <= 1'd1 << C_CORE;

                if ( ex_read_hit || ex_read_hit_r )

                    begin

                    select_way  <= data_hit_way | ex_read_hit_way;

                    c_state     <= CS_EX_DELETE;

                    source_sel  <= 1'd1 << C_INVA;

                    end

                else if ( read_miss )

                    begin

                    // wb read request asserted, wait for ack

                    if ( !i_wb_stall )

                        c_state <= CS_FILL1;

                    end

                else if ( write_hit )

                    c_state <= CS_WRITE_HIT1;

               end

             CS_FILL1 :

                begin

                // wb read request asserted, wait for ack

                if ( !i_wb_stall )

                    c_state <= CS_FILL2;

                end

             CS_FILL2 :

                // first read of burst of 4

                // wb read request asserted, wait for ack

                if ( !i_wb_stall )

                    c_state <= CS_FILL3;

             CS_FILL3 :

                // second read of burst of 4

                // wb read request asserted, wait for ack

                if ( !i_wb_stall )

                    c_state <= CS_FILL4;

             CS_FILL4 :

                // third read of burst of 4

                // wb read request asserted, wait for ack

                if ( !i_wb_stall )

                    begin

                    c_state     <= CS_FILL_COMPLETE;

                    source_sel  <= 1'd1 << C_FILL;

                    // Pick a way to write the cache update into

                    // Either pick one of the invalid caches, or if all are valid, then pick

                    // one randomly

                    select_way  <= next_way;

                    random_num  <= {random_num[2], random_num[1], random_num[0],

                                     random_num[3]^random_num[2]};

                    end

             // Write the read fetch data in this cycle

             CS_FILL_COMPLETE :

                // fourth read of burst of 4

                // wb read request asserted, wait for ack

                if ( !i_wb_stall )

                    begin

                    // Back to normal cache operations, but

                    // use physical address for first read as

                    // address moved before the stall was asserted for the read_miss

                    // However don't use it if its a non-cached address!

                    source_sel  <= 1'd1 << C_CORE;

                    c_state     <= CS_TURN_AROUND;

                    end

             // Ignore the tag read data in this cycle   

             // Wait 1 cycle to pre-read the cache and return to normal operation                 

             CS_TURN_AROUND :

                begin

                c_state     <= CS_IDLE;

                end

             // Flush the entry matching an exclusive access         

             CS_EX_DELETE:

                begin

                `ifdef A23_CACHE_DEBUG

                `TB_DEBUG_MESSAGE

                $display("Cache deleted Locked entry");

                `endif

                c_state    <= CS_TURN_AROUND;

                source_sel <= 1'd1 << C_CORE;

                end

             CS_WRITE_HIT1:

                begin

                // wait for an ack on the wb bus to complete the write

                if ( !i_wb_stall )

                    c_state     <= CS_IDLE;

                end

        endcase

// ======================================

// Capture WB Block Read - burst of 4 words

// ======================================

always @ ( posedge i_clk )

    if ( !i_wb_stall )

        wb_rdata_burst <= {i_wb_read_data, wb_rdata_burst[127:32]};

// ======================================

// WB Read Buffer

// ======================================

always @ ( posedge i_clk )

    begin

    if ( c_state == CS_FILL1 || c_state == CS_FILL2 ||

         c_state == CS_FILL3 || c_state == CS_FILL4 )

        begin

        if ( !i_wb_stall )

            begin

            wb_read_buf_valid   <= 1'd1;

            wb_read_buf_address <= i_wb_address;

            wb_read_buf_data    <= i_wb_read_data;

            end

        end

    else

        wb_read_buf_valid   <= 1'd0;

    end

// ======================================

// Miss Address

// ======================================

always @ ( posedge i_clk )

    if ( o_wb_req )

        miss_address <= i_address;

// ======================================

// Remember Read-Modify-Write Hit

// ======================================

assign ex_read_hit_clear = c_state == CS_EX_DELETE;

always @ ( posedge i_clk )

    if ( ex_read_hit_clear )

        begin

        ex_read_hit_r   <= 1'd0;

        ex_read_hit_way <= 'd0;

        end

    else if ( ex_read_hit )

        begin

        `ifdef A23_CACHE_DEBUG

            `TB_DEBUG_MESSAGE

            $display ("Exclusive access cache hit address 0x%08h", i_address);

        `endif

        ex_read_hit_r   <= 1'd1;

        ex_read_hit_way <= data_hit_way;

        end

    else if ( c_state == CS_FILL_COMPLETE && ex_read_hit_r )

        ex_read_hit_way <= select_way;

always @ (posedge i_clk)

    if ( ex_read_hit )

        ex_read_address <= i_address[CACHE_ADDR32_MSB:CACHE_ADDR32_LSB];

assign tag_address      = source_sel[C_FILL] ? miss_address      [CACHE_ADDR32_MSB:CACHE_ADDR32_LSB] :

                          source_sel[C_INVA] ? ex_read_address                                       :

                          source_sel[C_INIT] ? init_count[CACHE_ADDR_WIDTH-1:0]                      :

                          source_sel[C_CORE] ? address                                               :

                                               {CACHE_ADDR_WIDTH{1'd0}}                              ;

assign data_address     = write_hit          ? i_address   [CACHE_ADDR32_MSB:CACHE_ADDR32_LSB] :

                          source_sel[C_FILL] ? miss_address[CACHE_ADDR32_MSB:CACHE_ADDR32_LSB] :

                          source_sel[C_CORE] ? address                                         :

                                               {CACHE_ADDR_WIDTH{1'd0}}                        ;

assign tag_wdata        = source_sel[C_FILL] ? {1'd1, miss_address[31:TAG_ADDR32_LSB]} :

                                               {TAG_WIDTH{1'd0}}                       ;

    // Data comes in off the WB bus in wrap4 with the missed data word first

assign data_wdata       = write_hit && c_state == CS_IDLE ? write_hit_wdata : read_miss_wdata;

assign read_miss_wdata  = miss_address[3:2] == 2'd0 ? wb_rdata_burst                              :

                          miss_address[3:2] == 2'd1 ? { wb_rdata_burst[95:0], wb_rdata_burst[127:96] }:

                          miss_address[3:2] == 2'd2 ? { wb_rdata_burst[63:0], wb_rdata_burst[127:64] }:

                                                      { wb_rdata_burst[31:0], wb_rdata_burst[127:32] };

assign write_hit_wdata  = i_address[3:2] == 2'd0 ? {hit_rdata[127:32], write_data_word                   } :

                          i_address[3:2] == 2'd1 ? {hit_rdata[127:64], write_data_word, hit_rdata[31:0]  } :

                          i_address[3:2] == 2'd2 ? {hit_rdata[127:96], write_data_word, hit_rdata[63:0]  } :

                                                   {                   write_data_word, hit_rdata[95:0]  } ;

// Use Byte Enables

assign write_data_word  = i_byte_enable == 4'b0001 ? { o_read_data[31: 8], i_write_data[ 7: 0]                   } :

                          i_byte_enable == 4'b0010 ? { o_read_data[31:16], i_write_data[15: 8], o_read_data[ 7:0]} :

                          i_byte_enable == 4'b0100 ? { o_read_data[31:24], i_write_data[23:16], o_read_data[15:0]} :

                          i_byte_enable == 4'b1000 ? {                     i_write_data[31:24], o_read_data[23:0]} :

                          i_byte_enable == 4'b0011 ? { o_read_data[31:16], i_write_data[15: 0]                   } :

                          i_byte_enable == 4'b1100 ? {                     i_write_data[31:16], o_read_data[15:0]} :

                                                     i_write_data                                                  ;

assign tag_wenable      = source_sel[C_INVA] ? 1'd1  :

                          source_sel[C_FILL] ? 1'd1  :

                          source_sel[C_INIT] ? 1'd1  :

                          source_sel[C_CORE] ? 1'd0  :

                                               1'd0  ;

assign enable           = i_select && i_cache_enable;

assign exclusive_access = i_exclusive && i_cache_enable;

                          // the wb read buffer returns data directly from the wb bus to the

                          // core during a read miss operation

assign wb_read_buf_hit  = enable && wb_read_buf_address == i_address && wb_read_buf_valid;

assign hit              = |data_hit_way;

assign write_hit        = enable &&  i_write_enable && hit;

assign write_miss       = enable &&  i_write_enable && !hit && c_state != CS_WRITE_HIT1;

assign read_miss        = enable && !i_write_enable && !(hit || wb_read_buf_hit);

                          // Exclusive read hit

assign ex_read_hit      = exclusive_access && !i_write_enable && (hit || wb_read_buf_hit);

                          // Added to fix rare swap bug which occurs when the cache starts

                          // a fill just as the swap instruction starts to execute. The cache

                          // fails to check for a read hit on the swap read cycle.

                          // This signal stalls the core in that case until after the

                          // fill has completed.

assign ex_read_cache_busy = exclusive_access && !i_write_enable && c_state != CS_IDLE;

                          // Need to stall for a write miss to wait for the current wb 

                          // read miss access to complete. Also for a write hit, need 

                          // to stall for 1 cycle while the data cache is being written to

assign write_stall      = ( write_hit  && c_state != CS_WRITE_HIT1 ) ||

                          ( write_miss && ( c_state != CS_IDLE ) )   ||

                           i_wb_stall                                ;

assign read_stall       = read_miss;

                          // Core may or may not be trying to access cache memory during

                          // this phase of the read fetch. It could be doing e.g. a wb access

assign cache_busy_stall = ((c_state == CS_TURN_AROUND || c_state == CS_FILL1) && enable) ||

                           c_state == CS_INIT;

// ======================================

// Instantiate RAMS

// ======================================

generate

    for ( i=0; i<WAYS;i=i+1 ) begin : rams

        // Tag RAMs 

        `ifdef XILINX_SPARTAN6_FPGA

        xs6_sram_256x21_line_en

        `endif

        `ifdef XILINX_VIRTEX6_FPGA

        xv6_sram_256x21_line_en

        `endif

        `ifndef XILINX_FPGA

        generic_sram_line_en

        `endif

            #(

            .DATA_WIDTH                 ( TAG_WIDTH             ),

            .INITIALIZE_TO_ZERO         ( 1                     ),

            .ADDRESS_WIDTH              ( CACHE_ADDR_WIDTH      ))

        u_tag (

            .i_clk                      ( i_clk                 ),

            .i_write_data               ( tag_wdata             ),

            .i_write_enable             ( tag_wenable_way[i]    ),

            .i_address                  ( tag_address           ),

            .o_read_data                ( tag_rdata_way[i]      )

            );

        // Data RAMs 

        `ifdef XILINX_SPARTAN6_FPGA

        xs6_sram_256x128_byte_en

        `endif

        `ifdef XILINX_VIRTEX6_FPGA

        xv6_sram_256x128_byte_en

        `endif

        `ifndef XILINX_FPGA

        generic_sram_byte_en

        `endif

            #(

            .DATA_WIDTH    ( CACHE_LINE_WIDTH) ,

            .ADDRESS_WIDTH ( CACHE_ADDR_WIDTH) )

        u_data (

            .i_clk                      ( i_clk                         ),

            .i_write_data               ( data_wdata                    ),

            .i_write_enable             ( data_wenable_way[i]           ),

            .i_address                  ( data_address                  ),

            .i_byte_enable              ( {CACHE_LINE_WIDTH/8{1'd1}}    ),

            .o_read_data                ( data_rdata_way[i]             )

            );

        // Per tag-ram write-enable

        assign tag_wenable_way[i]  = tag_wenable && ( select_way[i] || source_sel[C_INIT] );

        // Per data-ram write-enable

        assign data_wenable_way[i] = (source_sel[C_FILL] && select_way[i]) ||

                                     (write_hit && data_hit_way[i] && c_state == CS_IDLE);

        // Per data-ram hit flag

        assign data_hit_way[i]     = tag_rdata_way[i][TAG_WIDTH-1] &&

                                     tag_rdata_way[i][TAG_ADDR_WIDTH-1:0] == i_address[31:TAG_ADDR32_LSB] &&

                                     c_state == CS_IDLE;

    end

endgenerate

// ======================================

// Register Valid Bits

// ======================================

generate

if ( WAYS == 2 ) begin : valid_bits_2ways

    always @ ( posedge i_clk )

        if ( c_state == CS_IDLE )

            valid_bits_r <= {tag_rdata_way[1][TAG_WIDTH-1],

                             tag_rdata_way[0][TAG_WIDTH-1]};

end

else if ( WAYS == 3 ) begin : valid_bits_3ways

    always @ ( posedge i_clk )

        if ( c_state == CS_IDLE )

            valid_bits_r <= {tag_rdata_way[2][TAG_WIDTH-1],

                             tag_rdata_way[1][TAG_WIDTH-1],

                             tag_rdata_way[0][TAG_WIDTH-1]};

end

else if ( WAYS == 4 ) begin : valid_bits_4ways

    always @ ( posedge i_clk )

        if ( c_state == CS_IDLE )

            valid_bits_r <= {tag_rdata_way[3][TAG_WIDTH-1],

                             tag_rdata_way[2][TAG_WIDTH-1],

                             tag_rdata_way[1][TAG_WIDTH-1],

                             tag_rdata_way[0][TAG_WIDTH-1]};

end

else begin : valid_bits_8ways

    always @ ( posedge i_clk )

        if ( c_state == CS_IDLE )

            valid_bits_r <= {tag_rdata_way[7][TAG_WIDTH-1],

                             tag_rdata_way[6][TAG_WIDTH-1],

                             tag_rdata_way[5][TAG_WIDTH-1],

                             tag_rdata_way[4][TAG_WIDTH-1],

                             tag_rdata_way[3][TAG_WIDTH-1],

                             tag_rdata_way[2][TAG_WIDTH-1],

                             tag_rdata_way[1][TAG_WIDTH-1],

                             tag_rdata_way[0][TAG_WIDTH-1]};

end

endgenerate

// ======================================

// Select read hit data

// ======================================

generate

if ( WAYS == 2 ) begin : read_data_2ways

    assign hit_rdata    = data_hit_way[0] ? data_rdata_way[0] :

                          data_hit_way[1] ? data_rdata_way[1] :

                                     {CACHE_LINE_WIDTH{1'd1}} ;  // all 1's for debug

end

else if ( WAYS == 3 ) begin : read_data_3ways

    assign hit_rdata    = data_hit_way[0] ? data_rdata_way[0] :

                          data_hit_way[1] ? data_rdata_way[1] :

                          data_hit_way[2] ? data_rdata_way[2] :

                                     {CACHE_LINE_WIDTH{1'd1}} ;  // all 1's for debug

end

else if ( WAYS == 4 ) begin : read_data_4ways

    assign hit_rdata    = data_hit_way[0] ? data_rdata_way[0] :