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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 MMU implementation

 Copyright (C) 2013 Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>

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

`include "mor1kx-defines.v"

module mor1kx_immu

  #(

    parameter FEATURE_IMMU_HW_TLB_RELOAD = "NONE",

    parameter OPTION_OPERAND_WIDTH = 32,

    parameter OPTION_IMMU_SET_WIDTH = 6,

    parameter OPTION_IMMU_WAYS = 1

    )

   (

    input                                 clk,

    input                                 rst,

    input                                 enable_i,

    output                                busy_o,

    input [OPTION_OPERAND_WIDTH-1:0]       virt_addr_i,

    input [OPTION_OPERAND_WIDTH-1:0]       virt_addr_match_i,

    output [OPTION_OPERAND_WIDTH-1:0]      phys_addr_o,

    output                                cache_inhibit_o,

    input                                 supervisor_mode_i,

    output                                tlb_miss_o,

    output                                pagefault_o,

    output reg                            tlb_reload_req_o,

    input                                 tlb_reload_ack_i,

    output reg [OPTION_OPERAND_WIDTH-1:0] tlb_reload_addr_o,

    input [OPTION_OPERAND_WIDTH-1:0]       tlb_reload_data_i,

    output                                tlb_reload_pagefault_o,

    input                                 tlb_reload_pagefault_clear_i,

    output                                tlb_reload_busy_o,

    // 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                                spr_bus_ack_o

    );

   wire [OPTION_OPERAND_WIDTH-1:0]    itlb_match_dout;

   wire [OPTION_IMMU_SET_WIDTH-1:0]   itlb_match_addr;

   wire                               itlb_match_we;

   wire [OPTION_OPERAND_WIDTH-1:0]    itlb_match_din;

   wire [OPTION_OPERAND_WIDTH-1:0]    itlb_match_huge_dout;

   wire [OPTION_IMMU_SET_WIDTH-1:0]   itlb_match_huge_addr;

   wire                               itlb_match_huge_we;

   wire [OPTION_OPERAND_WIDTH-1:0]    itlb_trans_dout;

   wire [OPTION_IMMU_SET_WIDTH-1:0]   itlb_trans_addr;

   wire                               itlb_trans_we;

   wire [OPTION_OPERAND_WIDTH-1:0]    itlb_trans_din;

   wire [OPTION_OPERAND_WIDTH-1:0]    itlb_trans_huge_dout;

   wire [OPTION_IMMU_SET_WIDTH-1:0]   itlb_trans_huge_addr;

   wire                               itlb_trans_huge_we;

   reg                                itlb_match_reload_we;

   reg [OPTION_OPERAND_WIDTH-1:0]     itlb_match_reload_din;

   reg                                itlb_trans_reload_we;

   reg [OPTION_OPERAND_WIDTH-1:0]     itlb_trans_reload_din;

   wire                               itlb_match_spr_cs;

   reg                                itlb_match_spr_cs_r;

   wire                               itlb_trans_spr_cs;

   reg                                itlb_trans_spr_cs_r;

   wire                               immucr_spr_cs;

   reg                                immucr_spr_cs_r;

   reg [OPTION_OPERAND_WIDTH-1:0]     immucr;

   wire                               tlb_huge;

   wire                               tlb_miss;

   wire                               tlb_huge_miss;

   reg                                tlb_reload_pagefault;

   reg                                tlb_reload_huge;

   // sxe: supervisor execute enable

   // uxe: user exexute enable

   wire                               sxe;

   wire                               uxe;

   reg                                spr_bus_ack;

   reg                                spr_bus_ack_r;

   wire [OPTION_OPERAND_WIDTH-1:0]    spr_bus_dat;

   reg [OPTION_OPERAND_WIDTH-1:0]     spr_bus_dat_r;

   always @(posedge clk `OR_ASYNC_RST)

     if (rst)

       spr_bus_ack <= 0;

     else if (spr_bus_stb_i & spr_bus_addr_i[15:11] == 5'd2)

       spr_bus_ack <= 1;

     else

       spr_bus_ack <= 0;

   always @(posedge clk)

     spr_bus_ack_r <= spr_bus_ack;

   always @(posedge clk)

     if (spr_bus_ack & !spr_bus_ack_r)

       spr_bus_dat_r <= spr_bus_dat;

   assign spr_bus_ack_o = spr_bus_ack & spr_bus_stb_i &

                          spr_bus_addr_i[15:11] == 5'd2;

   assign cache_inhibit_o = tlb_huge ? itlb_trans_huge_dout[1] :

                             itlb_trans_dout[1];

   assign sxe = tlb_huge ? itlb_trans_huge_dout[6] : itlb_trans_dout[6];

   assign uxe = tlb_huge ? itlb_trans_huge_dout[7] : itlb_trans_dout[7];

   assign pagefault_o = (supervisor_mode_i ? !sxe : !uxe) &

                        !tlb_reload_busy_o & !busy_o;

   assign busy_o = ((itlb_match_spr_cs | itlb_trans_spr_cs) & !spr_bus_ack |

                    (itlb_match_spr_cs_r | itlb_trans_spr_cs_r) &

                    spr_bus_ack & !spr_bus_ack_r) & enable_i;

   always @(posedge clk `OR_ASYNC_RST)

     if (rst) begin

        itlb_match_spr_cs_r <= 0;

        itlb_trans_spr_cs_r <= 0;

        immucr_spr_cs_r <= 0;

     end else begin

        itlb_match_spr_cs_r <= itlb_match_spr_cs;

        itlb_trans_spr_cs_r <= itlb_trans_spr_cs;

        immucr_spr_cs_r <= immucr_spr_cs;

     end

generate /* verilator lint_off WIDTH */

if (FEATURE_IMMU_HW_TLB_RELOAD == "ENABLED") begin

/* verilator lint_on WIDTH */

   assign immucr_spr_cs = spr_bus_stb_i &

                          spr_bus_addr_i == `OR1K_SPR_IMMUCR_ADDR;

   always @(posedge clk `OR_ASYNC_RST)

     if (rst)

       immucr <= 0;

     else if (immucr_spr_cs & spr_bus_we_i)

       immucr <= spr_bus_dat_i;

end else begin

   assign immucr_spr_cs = 0;

   always @(posedge clk)

     immucr <= 0;

end

endgenerate

   // TODO: optimize this

   assign itlb_match_spr_cs = spr_bus_stb_i &

                              (spr_bus_addr_i >= `OR1K_SPR_ITLBW0MR0_ADDR) &

                              (spr_bus_addr_i < `OR1K_SPR_ITLBW0TR0_ADDR);

   assign itlb_trans_spr_cs = spr_bus_stb_i &

                              (spr_bus_addr_i >= `OR1K_SPR_ITLBW0TR0_ADDR) &

                              (spr_bus_addr_i < `OR1K_SPR_ITLBW1MR0_ADDR);

   assign itlb_match_addr = itlb_match_spr_cs & !spr_bus_ack ?

                            spr_bus_addr_i[OPTION_IMMU_SET_WIDTH-1:0] :

                            virt_addr_i[13+(OPTION_IMMU_SET_WIDTH-1):13];

   assign itlb_trans_addr = itlb_trans_spr_cs & !spr_bus_ack ?

                            spr_bus_addr_i[OPTION_IMMU_SET_WIDTH-1:0] :

                            virt_addr_i[13+(OPTION_IMMU_SET_WIDTH-1):13];

   assign itlb_match_we = itlb_match_spr_cs & spr_bus_we_i & !spr_bus_ack |

                          itlb_match_reload_we & !tlb_reload_huge;

   assign itlb_trans_we = itlb_trans_spr_cs & spr_bus_we_i & !spr_bus_ack |

                          itlb_trans_reload_we & !tlb_reload_huge;

   assign itlb_match_din = itlb_match_spr_cs & spr_bus_we_i & !spr_bus_ack ?

                           spr_bus_dat_i : itlb_match_reload_din;

   assign itlb_trans_din = itlb_trans_spr_cs & spr_bus_we_i & !spr_bus_ack ?

                           spr_bus_dat_i : itlb_trans_reload_din;

   assign itlb_match_huge_addr = virt_addr_i[24+(OPTION_IMMU_SET_WIDTH-1):24];

   assign itlb_trans_huge_addr = virt_addr_i[24+(OPTION_IMMU_SET_WIDTH-1):24];

   assign itlb_match_huge_we = itlb_match_reload_we & tlb_reload_huge;

   assign itlb_trans_huge_we = itlb_trans_reload_we & tlb_reload_huge;

   assign spr_bus_dat = itlb_match_spr_cs_r ? itlb_match_dout :

                        itlb_trans_spr_cs_r ? itlb_trans_dout :

                        immucr_spr_cs_r ? immucr : 0;

   // Use registered value on all but the first cycle spr_bus_ack is asserted

   assign spr_bus_dat_o = spr_bus_ack & !spr_bus_ack_r ? spr_bus_dat :

                          spr_bus_dat_r;

   assign tlb_huge = &itlb_match_huge_dout[1:0]; // huge & valid

   assign tlb_miss = itlb_match_dout[31:13] != virt_addr_match_i[31:13] |

                     !itlb_match_dout[0];  // valid bit

   assign tlb_huge_miss = itlb_match_huge_dout[31:24] !=

                          virt_addr_match_i[31:24] | !itlb_match_huge_dout[0];

   assign tlb_miss_o = (tlb_miss & !tlb_huge | tlb_huge_miss & tlb_huge) &

                       !tlb_reload_pagefault & !busy_o;

   assign phys_addr_o = tlb_huge ?

                        {itlb_trans_huge_dout[31:24], virt_addr_match_i[23:0]} :

                        {itlb_trans_dout[31:13], virt_addr_match_i[12:0]};

generate /* verilator lint_off WIDTH */

if (FEATURE_IMMU_HW_TLB_RELOAD == "ENABLED") begin

   /* verilator lint_on WIDTH */

   // Hardware TLB reload

   // Compliant with the suggestions outlined in this thread:

   // http://lists.openrisc.net/pipermail/openrisc/2013-July/001806.html

   //

   // PTE layout:

   // | 31 ... 13 | 12 |  11 |   10  | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |

   // |    PPN    | Reserved |PRESENT| L | X | W | U | D | A |WOM|WBC|CI |CC |

   //

   // Where X/W/U maps into SXE/UXE like this:

   // X | W | U   SXE | UXE

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

   // 0 | x | 0 =  0  |  0

   // 0 | x | 1 =  0  |  0

   //    ...

   // 1 | x | 0 =  1  |  0

   // 1 | x | 1 =  1  |  1

   localparam TLB_IDLE                  = 2'd0;

   localparam TLB_GET_PTE_POINTER       = 2'd1;

   localparam TLB_GET_PTE               = 2'd2;

   localparam TLB_READ                  = 2'd3;

   reg [1:0] tlb_reload_state = TLB_IDLE;

   wire      do_reload;

   assign do_reload = enable_i & tlb_miss_o & (immucr[31:10] != 0);

   assign tlb_reload_busy_o = (tlb_reload_state != TLB_IDLE) | do_reload;

   assign tlb_reload_pagefault_o = tlb_reload_pagefault &

                                    !tlb_reload_pagefault_clear_i;

   always @(posedge clk) begin

      if (tlb_reload_pagefault_clear_i | rst)

        tlb_reload_pagefault <= 0;

      itlb_trans_reload_we <= 0;

      itlb_trans_reload_din <= 0;

      itlb_match_reload_we <= 0;

      itlb_match_reload_din <= 0;

      case (tlb_reload_state)

        TLB_IDLE: begin

           tlb_reload_huge <= 0;

           tlb_reload_req_o <= 0;

           if (do_reload) begin

              tlb_reload_req_o <= 1;

              tlb_reload_addr_o <= {immucr[31:10],

                                    virt_addr_match_i[31:24], 2'b00};

              tlb_reload_state <= TLB_GET_PTE_POINTER;

           end

        end

        //

        // Here we get the pointer to the PTE table, next is to fetch

        // the actual pte from the offset in the table.

        // The offset is calculated by:

        // ((virt_addr_match >> PAGE_BITS) & (PTE_CNT-1)) << 2

        // Where PAGE_BITS is 13 (8 kb page) and PTE_CNT is 2048

        // (number of PTEs in the PTE table)

        //

        TLB_GET_PTE_POINTER: begin

           tlb_reload_huge <= 0;

           if (tlb_reload_ack_i) begin

              if (tlb_reload_data_i[31:13] == 0) begin

                 tlb_reload_pagefault <= 1;

                 tlb_reload_req_o <= 0;

                 tlb_reload_state <= TLB_IDLE;

              end else if (tlb_reload_data_i[9]) begin

                 tlb_reload_huge <= 1;

                 tlb_reload_req_o <= 0;

                 tlb_reload_state <= TLB_GET_PTE;

              end else begin

                 tlb_reload_addr_o <= {tlb_reload_data_i[31:13],

                                       virt_addr_match_i[23:13], 2'b00};

                 tlb_reload_state <= TLB_GET_PTE;

              end

           end

        end

        //

        // Here we get the actual PTE, left to do is to translate the

        // PTE data into our translate and match registers.

        //

        TLB_GET_PTE: begin

           if (tlb_reload_ack_i) begin

              tlb_reload_req_o <= 0;

              // Check PRESENT bit

              if (!tlb_reload_data_i[10]) begin

                 tlb_reload_pagefault <= 1;

                 tlb_reload_state <= TLB_IDLE;

              end else begin

                 // Translate register generation.

                 // PPN

                 itlb_trans_reload_din[31:13] <= tlb_reload_data_i[31:13];

                 // UXE = X & U

                 itlb_trans_reload_din[7] <= tlb_reload_data_i[8] &

                                              tlb_reload_data_i[6];

                 // SXE = X

                 itlb_trans_reload_din[6] <= tlb_reload_data_i[8];

                 // Dirty, Accessed, Weakly-Ordered-Memory, Writeback cache,

                 // Cache inhibit, Cache coherent

                 itlb_trans_reload_din[5:0] <= tlb_reload_data_i[5:0];

                 itlb_trans_reload_we <= 1;

                 // Match register generation.

                 // VPN

                 itlb_match_reload_din[31:13] <= virt_addr_match_i[31:13];

                 // PL1

                 itlb_match_reload_din[1] <= tlb_reload_huge;

                 // Valid

                 itlb_match_reload_din[0] <= 1;

                 itlb_match_reload_we <= 1;

                 tlb_reload_state <= TLB_READ;

              end

           end

        end

        // Let the just written values propagate out on the read ports

        TLB_READ: begin

           tlb_reload_state <= TLB_IDLE;

        end

        default:

          tlb_reload_state <= TLB_IDLE;

      endcase

   end

end else begin // if (FEATURE_IMMU_HW_TLB_RELOAD == "ENABLED")

   assign tlb_reload_pagefault_o = 0;

   assign tlb_reload_busy_o = 0;

   always @(posedge clk) begin

      tlb_reload_req_o <= 0;

      tlb_reload_addr_o <= 0;

      tlb_reload_pagefault <= 0;

      itlb_trans_reload_we <= 0;

      itlb_trans_reload_din <= 0;

      itlb_match_reload_we <= 0;

      itlb_match_reload_din <= 0;

   end

end

endgenerate

   // ITLB match registers

   mor1kx_true_dpram_sclk

     #(

       .ADDR_WIDTH(OPTION_IMMU_SET_WIDTH),

       .DATA_WIDTH(OPTION_OPERAND_WIDTH)

       )

   itlb_match_regs

     (

      // Outputs

      .dout_a                           (itlb_match_dout),

      .dout_b                           (itlb_match_huge_dout),

      // Inputs

      .clk                              (clk),

      .addr_a                           (itlb_match_addr),

      .we_a                             (itlb_match_we),

      .din_a                            (itlb_match_din),

      .addr_b                           (itlb_match_huge_addr),

      .we_b                             (itlb_match_huge_we),

      .din_b                            (itlb_match_reload_din)

      );

   // ITLB translate registers

   mor1kx_true_dpram_sclk

     #(

       .ADDR_WIDTH(OPTION_IMMU_SET_WIDTH),

       .DATA_WIDTH(OPTION_OPERAND_WIDTH)

       )

   itlb_translate_regs

     (

      // Outputs

      .dout_a                           (itlb_trans_dout),

      .dout_b                           (itlb_trans_huge_dout),

      // Inputs

      .clk                              (clk),

      .addr_a                           (itlb_trans_addr),

      .we_a                             (itlb_trans_we),

      .din_a                            (itlb_trans_din),

      .addr_b                           (itlb_trans_huge_addr),

      .we_b                             (itlb_trans_huge_we),

      .din_b                            (itlb_trans_reload_din)

      );

endmodule