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

 This Source Code Form is subject to the terms of the

 Open Hardware Description License, v. 1.0. If a copy

 of the OHDL was not distributed with this file, You

 can obtain one at http://juliusbaxter.net/ohdl/ohdl.txt

 Description: Instruction cache implementation

 Copyright (C) 2012-2013

    Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>

    Stefan Wallentowitz <stefan.wallentowitz@tum.de>

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

`include "mor1kx-defines.v"

module mor1kx_icache

  #(

    parameter OPTION_OPERAND_WIDTH = 32,

    parameter OPTION_ICACHE_BLOCK_WIDTH = 5,

    parameter OPTION_ICACHE_SET_WIDTH = 9,

    parameter OPTION_ICACHE_WAYS = 2,

    parameter OPTION_ICACHE_LIMIT_WIDTH = 32

    )

   (

    input                             clk,

    input                             rst,

    input                             ic_access_i,

    output                            refill_o,

    output                            refill_req_o,

    output                            refill_done_o,

    output                            invalidate_o,

    // CPU Interface

    output                            cpu_ack_o,

    output reg [`OR1K_INSN_WIDTH-1:0] cpu_dat_o,

    input [OPTION_OPERAND_WIDTH-1:0]  cpu_adr_i,

    input [OPTION_OPERAND_WIDTH-1:0]  cpu_adr_match_i,

    input                             cpu_req_i,

    input [OPTION_OPERAND_WIDTH-1:0]  wradr_i,

    input [`OR1K_INSN_WIDTH-1:0]      wrdat_i,

    input                             we_i,

    // SPR interface

    input [15:0]                       spr_bus_addr_i,

    input                             spr_bus_we_i,

    input                             spr_bus_stb_i,

    input [OPTION_OPERAND_WIDTH-1:0]  spr_bus_dat_i,

    output [OPTION_OPERAND_WIDTH-1:0] spr_bus_dat_o,

    output reg                        spr_bus_ack_o

    );

   // States

   localparam IDLE              = 4'b0001;

   localparam READ              = 4'b0010;

   localparam REFILL            = 4'b0100;

   localparam INVALIDATE        = 4'b1000;

   // Address space in bytes for a way

   localparam WAY_WIDTH = OPTION_ICACHE_BLOCK_WIDTH + OPTION_ICACHE_SET_WIDTH;

   /*

    * Tag memory layout

    *            +---------------------------------------------------------+

    * (index) -> | LRU | wayN valid | wayN tag |...| way0 valid | way0 tag |

    *            +---------------------------------------------------------+

    */

   // The tag is the part left of the index

   localparam TAG_WIDTH = (OPTION_ICACHE_LIMIT_WIDTH - WAY_WIDTH);

   // The tag memory contains entries with OPTION_ICACHE_WAYS parts of

   // each TAGMEM_WAY_WIDTH. Each of those is tag and a valid flag.

   localparam TAGMEM_WAY_WIDTH = TAG_WIDTH + 1;

   localparam TAGMEM_WAY_VALID = TAGMEM_WAY_WIDTH - 1;

   // Additionally, the tag memory entry contains an LRU value. The

   // width of this is actually 0 for OPTION_ICACHE_LIMIT_WIDTH==1

   localparam TAG_LRU_WIDTH = OPTION_ICACHE_WAYS*(OPTION_ICACHE_WAYS-1) >> 1;

   // We have signals for the LRU which are not used for one way

   // caches. To avoid signal width [-1:0] this generates [0:0]

   // vectors for them, which are removed automatically then.

   localparam TAG_LRU_WIDTH_BITS = (OPTION_ICACHE_WAYS >= 2) ? TAG_LRU_WIDTH : 1;

   // Compute the total sum of the entry elements

   localparam TAGMEM_WIDTH = TAGMEM_WAY_WIDTH * OPTION_ICACHE_WAYS + TAG_LRU_WIDTH;

   // For convenience we define the position of the LRU in the tag

   // memory entries

   localparam TAG_LRU_MSB = TAGMEM_WIDTH - 1;

   localparam TAG_LRU_LSB = TAG_LRU_MSB - TAG_LRU_WIDTH + 1;

   // FSM state signals

   reg [3:0]                           state;

   wire                               idle;

   wire                               read;

   wire                               refill;

   wire                               invalidate;

   reg [WAY_WIDTH-1:OPTION_ICACHE_BLOCK_WIDTH] invalidate_adr;

   wire [31:0]                         next_refill_adr;

   wire                               refill_done;

   wire                               refill_hit;

   reg [(1<<(OPTION_ICACHE_BLOCK_WIDTH-2))-1:0] refill_valid;

   reg [(1<<(OPTION_ICACHE_BLOCK_WIDTH-2))-1:0] refill_valid_r;

   // The index we read and write from tag memory

   wire [OPTION_ICACHE_SET_WIDTH-1:0] tag_rindex;

   wire [OPTION_ICACHE_SET_WIDTH-1:0] tag_windex;

   // The data from the tag memory

   wire [TAGMEM_WIDTH-1:0]             tag_dout;

   wire [TAG_LRU_WIDTH_BITS-1:0]      tag_lru_out;

   wire [TAGMEM_WAY_WIDTH-1:0]         tag_way_out [OPTION_ICACHE_WAYS-1:0];

   // The data to the tag memory

   wire [TAGMEM_WIDTH-1:0]             tag_din;

   reg [TAG_LRU_WIDTH_BITS-1:0]       tag_lru_in;

   reg [TAGMEM_WAY_WIDTH-1:0]          tag_way_in [OPTION_ICACHE_WAYS-1:0];

   reg [TAGMEM_WAY_WIDTH-1:0]          tag_way_save [OPTION_ICACHE_WAYS-1:0];

   // Whether to write to the tag memory in this cycle

   reg                                tag_we;

   // This is the tag we need to write to the tag memory during refill

   wire [TAG_WIDTH-1:0]        tag_wtag;

   // This is the tag we check against

   wire [TAG_WIDTH-1:0]        tag_tag;

   // Access to the way memories

   wire [WAY_WIDTH-3:0]        way_raddr[OPTION_ICACHE_WAYS-1:0];

   wire [WAY_WIDTH-3:0]        way_waddr[OPTION_ICACHE_WAYS-1:0];

   wire [OPTION_OPERAND_WIDTH-1:0]    way_din[OPTION_ICACHE_WAYS-1:0];

   wire [OPTION_OPERAND_WIDTH-1:0]    way_dout[OPTION_ICACHE_WAYS-1:0];

   reg [OPTION_ICACHE_WAYS-1:0]       way_we;

   // Does any way hit?

   wire                               hit;

   wire [OPTION_ICACHE_WAYS-1:0]      way_hit;

   // This is the least recently used value before access the memory.

   // Those are one hot encoded.

   wire [OPTION_ICACHE_WAYS-1:0]      lru;

   // Register that stores the LRU value from lru

   reg [OPTION_ICACHE_WAYS-1:0]       tag_save_lru;

   // The access vector to update the LRU history is the way that has

   // a hit or is refilled. It is also one-hot encoded.

   reg [OPTION_ICACHE_WAYS-1:0]       access;

   // The current LRU history as read from tag memory and the update

   // value after we accessed it to write back to tag memory.

   wire [TAG_LRU_WIDTH_BITS-1:0]      current_lru_history;

   wire [TAG_LRU_WIDTH_BITS-1:0]      next_lru_history;

   // Intermediate signals to ease debugging

   wire [TAG_WIDTH-1:0]               check_way_tag [OPTION_ICACHE_WAYS-1:0];

   wire                               check_way_match [OPTION_ICACHE_WAYS-1:0];

   wire                               check_way_valid [OPTION_ICACHE_WAYS-1:0];

   genvar                             i;

   // Allowing (out of the cache line being refilled) accesses during refill

   // exposes a bug somewhere, causing the Linux kernel to end up with a

   // bus error UNHANDLED EXCEPTION.

   // Until that is sorted out, disable it.

   assign cpu_ack_o = (read /*| refill & ic_access_i*/) & hit |

                      refill_hit & ic_access_i;

   assign tag_rindex = cpu_adr_i[WAY_WIDTH-1:OPTION_ICACHE_BLOCK_WIDTH];

   /*

    * The tag mem is written during reads to write the lru info and during

    * refill and invalidate

    */

   assign tag_windex = read ?

                       cpu_adr_match_i[WAY_WIDTH-1:OPTION_ICACHE_BLOCK_WIDTH] :

                       invalidate ? invalidate_adr :

                       wradr_i[WAY_WIDTH-1:OPTION_ICACHE_BLOCK_WIDTH];

   assign tag_tag = cpu_adr_match_i[OPTION_ICACHE_LIMIT_WIDTH-1:WAY_WIDTH];

   assign tag_wtag = wradr_i[OPTION_ICACHE_LIMIT_WIDTH-1:WAY_WIDTH];

   generate

      if (OPTION_ICACHE_WAYS >= 2) begin

         // Multiplex the LRU history from and to tag memory

         assign current_lru_history = tag_dout[TAG_LRU_MSB:TAG_LRU_LSB];

         assign tag_din[TAG_LRU_MSB:TAG_LRU_LSB] = tag_lru_in;

         assign tag_lru_out = tag_dout[TAG_LRU_MSB:TAG_LRU_LSB];

      end

      for (i = 0; i < OPTION_ICACHE_WAYS; i=i+1) begin : ways

         assign way_raddr[i] = cpu_adr_i[WAY_WIDTH-1:2];

         assign way_waddr[i] = wradr_i[WAY_WIDTH-1:2];

         assign way_din[i] = wrdat_i;

         // compare stored tag with incoming tag and check valid bit

         assign check_way_tag[i] = tag_way_out[i][TAG_WIDTH-1:0];

         assign check_way_match[i] = (check_way_tag[i] == tag_tag);

         assign check_way_valid[i] = tag_way_out[i][TAGMEM_WAY_VALID];

         assign way_hit[i] = check_way_valid[i] & check_way_match[i];

         // Multiplex the way entries in the tag memory

         assign tag_din[(i+1)*TAGMEM_WAY_WIDTH-1:i*TAGMEM_WAY_WIDTH] = tag_way_in[i];

         assign tag_way_out[i] = tag_dout[(i+1)*TAGMEM_WAY_WIDTH-1:i*TAGMEM_WAY_WIDTH];

      end

   endgenerate

   assign hit = |way_hit;

   integer w0;

   always @(*) begin

      cpu_dat_o = {OPTION_OPERAND_WIDTH{1'bx}};

      // Put correct way on the data port

      for (w0 = 0; w0 < OPTION_ICACHE_WAYS; w0 = w0 + 1) begin

         if (way_hit[w0] | (refill_hit & tag_save_lru[w0])) begin

            cpu_dat_o = way_dout[w0];

         end

      end

   end

   assign next_refill_adr = (OPTION_ICACHE_BLOCK_WIDTH == 5) ?

                            {wradr_i[31:5], wradr_i[4:0] + 5'd4} : // 32 byte

                            {wradr_i[31:4], wradr_i[3:0] + 4'd4};  // 16 byte

   assign refill_done_o = refill_done;

   assign refill_done = refill_valid[next_refill_adr[OPTION_ICACHE_BLOCK_WIDTH-1:2]];

   assign refill_hit = refill_valid_r[cpu_adr_match_i[OPTION_ICACHE_BLOCK_WIDTH-1:2]] &

                       cpu_adr_match_i[OPTION_ICACHE_LIMIT_WIDTH-1:

                                       OPTION_ICACHE_BLOCK_WIDTH] ==

                       wradr_i[OPTION_ICACHE_LIMIT_WIDTH-1:

                               OPTION_ICACHE_BLOCK_WIDTH] &

                       refill;

   assign idle = (state == IDLE);

   assign refill = (state == REFILL);

   assign read = (state == READ);

   assign invalidate = (state == INVALIDATE);

   assign refill_o = refill;

   assign refill_req_o = read & cpu_req_i & !hit | refill;

   /*

    * SPR bus interface

    */

   assign invalidate_o = spr_bus_stb_i & spr_bus_we_i &

                         (spr_bus_addr_i == `OR1K_SPR_ICBIR_ADDR);

   /*

    * Cache FSM

    */

   integer w1;

   always @(posedge clk `OR_ASYNC_RST) begin

      refill_valid_r <= refill_valid;

      spr_bus_ack_o <= 0;

      case (state)

        IDLE: begin

           if (cpu_req_i)

             state <= READ;

        end

        READ: begin

           if (ic_access_i) begin

              if (hit) begin

                 state <= READ;

              end else if (cpu_req_i) begin

                 refill_valid <= 0;

                 refill_valid_r <= 0;

                 // Store the LRU information for correct replacement

                 // on refill. Always one when only one way.

                 tag_save_lru <= (OPTION_ICACHE_WAYS==1) | lru;

                 for (w1 = 0; w1 < OPTION_ICACHE_WAYS; w1 = w1 + 1) begin

                    tag_way_save[w1] <= tag_way_out[w1];

                 end

                 state <= REFILL;

              end

           end else begin

              state <= IDLE;

           end

        end

        REFILL: begin

           if (we_i) begin

              refill_valid[wradr_i[OPTION_ICACHE_BLOCK_WIDTH-1:2]] <= 1;

              if (refill_done)

                state <= IDLE;

           end

        end

        INVALIDATE: begin

           if (!invalidate_o)

             state <= IDLE;

           spr_bus_ack_o <= 1;

        end

        default:

          state <= IDLE;

      endcase

      if (invalidate_o & !refill) begin

         invalidate_adr <= spr_bus_dat_i[WAY_WIDTH-1:OPTION_ICACHE_BLOCK_WIDTH];

         spr_bus_ack_o <= 1;

         state <= INVALIDATE;

      end

      if (rst)

        state <= IDLE;

   end

   integer w2;

   always @(*) begin

      // Default is to keep data, don't write and don't access

      tag_lru_in = tag_lru_out;

      for (w2 = 0; w2 < OPTION_ICACHE_WAYS; w2 = w2 + 1) begin

         tag_way_in[w2] = tag_way_out[w2];

      end

      tag_we = 1'b0;

      way_we = {(OPTION_ICACHE_WAYS){1'b0}};

      access = {(OPTION_ICACHE_WAYS){1'b0}};

      case (state)

        READ: begin

           if (hit) begin

              // We got a hit. The LRU module gets the access

              // information. Depending on this we update the LRU

              // history in the tag.

              access = way_hit;

              // This is the updated LRU history after hit

              tag_lru_in = next_lru_history;

              tag_we = 1'b1;

           end

        end

        REFILL: begin

           if (we_i) begin

              // Write the data to the way that is replaced (which is

              // the LRU)

              way_we = tag_save_lru;

              // Access pattern

              access = tag_save_lru;

              /* Invalidate the way on the first write */

              if (refill_valid == 0) begin

                 for (w2 = 0; w2 < OPTION_ICACHE_WAYS; w2 = w2 + 1) begin

                    if (tag_save_lru[w2]) begin

                       tag_way_in[w2][TAGMEM_WAY_VALID] = 1'b0;

                    end

                 end

                 tag_we = 1'b1;

              end

              // After refill update the tag memory entry of the

              // filled way with the LRU history, the tag and set

              // valid to 1.

              if (refill_done) begin

                 for (w2 = 0; w2 < OPTION_ICACHE_WAYS; w2 = w2 + 1) begin

                    tag_way_in[w2] = tag_way_save[w2];

                    if (tag_save_lru[w2]) begin

                       tag_way_in[w2] = { 1'b1, tag_wtag };

                    end

                 end

                 tag_lru_in = next_lru_history;

                 tag_we = 1'b1;

              end

           end

        end

        INVALIDATE: begin

           // Lazy invalidation, invalidate everything that matches tag address

           tag_lru_in = 0;

           for (w2 = 0; w2 < OPTION_ICACHE_WAYS; w2 = w2 + 1) begin

              tag_way_in[w2] = 0;

           end

           tag_we = 1'b1;

        end

        default: begin

        end

      endcase

   end

   /* mor1kx_simple_dpram_sclk AUTO_TEMPLATE (

      // Outputs

      .dout                     (way_dout[i][OPTION_OPERAND_WIDTH-1:0]),

      // Inputs

      .raddr                    (way_raddr[i][WAY_WIDTH-3:0]),

      .re                       (1'b1),

      .waddr                    (way_waddr[i][WAY_WIDTH-3:0]),

      .we                       (way_we[i]),

      .din                      (way_din[i][31:0]));

    */

   generate

      for (i = 0; i < OPTION_ICACHE_WAYS; i=i+1) begin : way_memories

         mor1kx_simple_dpram_sclk

               #(

                 .ADDR_WIDTH(WAY_WIDTH-2),

                 .DATA_WIDTH(OPTION_OPERAND_WIDTH),

                 .ENABLE_BYPASS(0)

                 )

         way_data_ram

               (/*AUTOINST*/

                // Outputs

                .dout                   (way_dout[i][OPTION_OPERAND_WIDTH-1:0]), // Templated

                // Inputs

                .clk                    (clk),

                .raddr                  (way_raddr[i][WAY_WIDTH-3:0]), // Templated

                .re                     (1'b1),                  // Templated

                .waddr                  (way_waddr[i][WAY_WIDTH-3:0]), // Templated

                .we                     (way_we[i]),             // Templated

                .din                    (way_din[i][31:0]));      // Templated

      end // block: way_memories

      if (OPTION_ICACHE_WAYS >= 2) begin : gen_u_lru

         /* mor1kx_cache_lru AUTO_TEMPLATE(

          .current  (current_lru_history),

          .update   (next_lru_history),

          .lru_pre  (lru),

          .lru_post (),

          .access   (access),

          ); */

         mor1kx_cache_lru

           #(.NUMWAYS(OPTION_ICACHE_WAYS))

         u_lru(/*AUTOINST*/

               // Outputs

               .update                  (next_lru_history),      // Templated

               .lru_pre                 (lru),                   // Templated

               .lru_post                (),                      // Templated

               // Inputs

               .current                 (current_lru_history),   // Templated

               .access                  (access));               // Templated

      end // if (OPTION_ICACHE_WAYS >= 2)

   endgenerate

   /* mor1kx_simple_dpram_sclk AUTO_TEMPLATE (

      // Outputs

      .dout                     (tag_dout[TAGMEM_WIDTH-1:0]),

      // Inputs

      .raddr                    (tag_rindex),

      .re                       (1'b1),

      .waddr                    (tag_windex),

      .we                       (tag_we),

      .din                      (tag_din));

    */

   mor1kx_simple_dpram_sclk

     #(

       .ADDR_WIDTH(OPTION_ICACHE_SET_WIDTH),

       .DATA_WIDTH(TAGMEM_WIDTH),

       .ENABLE_BYPASS(0)

     )

   tag_ram

     (/*AUTOINST*/

      // Outputs

      .dout                             (tag_dout[TAGMEM_WIDTH-1:0]), // Templated

      // Inputs

      .clk                              (clk),

      .raddr                            (tag_rindex),            // Templated

      .re                               (1'b1),                  // Templated

      .waddr                            (tag_windex),            // Templated

      .we                               (tag_we),                // Templated

      .din                              (tag_din));              // Templated

endmodule