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

//

//  WISHBONE revB.2 compliant Xgate Coprocessor - Slave Bus interface

//

//  Author: Bob Hayes

//          rehayes@opencores.org

//

//  Downloaded from: http://www.opencores.org/projects/xgate.....

//

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

// Copyright (c) 2009, Robert Hayes

//

// 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 3 of the License, or

// (at your option) any later version.

//

// Supplemental terms.

//     * Redistributions of source code must retain the above copyright

//       notice, this list of conditions and the following disclaimer.

//     * Neither the name of the <organization> 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 Robert Hayes ''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 Robert Hayes 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.

//

// You should have received a copy of the GNU General Public License

// along with this program.  If not, see <http://www.gnu.org/licenses/>.

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

// 45678901234567890123456789012345678901234567890123456789012345678901234567890

module xgate_wbs_bus #(parameter ARST_LVL = 1'b0,    // asynchronous reset level

                       parameter DWIDTH = 16,

                       parameter WB_RD_DEFAULT = 0,  // WISHBONE Read Bus default state

                       parameter SINGLE_CYCLE = 1'b0)

  (

  // Wishbone Signals

  output      [DWIDTH-1:0] wbs_dat_o,     // databus output - Pseudo Register

  output                   wbs_ack_o,     // bus cycle acknowledge output

  output                   wbs_err_o,     // bus error, lost module select durning wait state

  input                    wbs_clk_i,     // master clock input

  input                    wbs_rst_i,     // synchronous active high reset

  input                    arst_i,        // asynchronous reset

  input             [ 6:1] wbs_adr_i,     // lower address bits

  input       [DWIDTH-1:0] wbs_dat_i,     // databus input

  input                    wbs_we_i,      // write enable input

  input                    wbs_stb_i,     // stobe/core select signal

  input                    wbs_cyc_i,     // valid bus cycle input

  input              [1:0] wbs_sel_i,     // Select byte in word bus transaction

  // XGATE Control Signals

  output reg               write_xgmctl, // Write Strobe for XGMCTL register

  output reg               write_xgchid, // Write Strobe for XGCHID register

  output reg               write_xgisp74,// Write Strobe for XGISP74 register

  output reg               write_xgisp30,// Write Strobe for XGISP30 register

  output reg         [1:0] write_xgvbr,  // Write Strobe for XGVBR register

  output reg         [1:0] write_xgif_7, // Write Strobe for Interrupt Flag Register 7

  output reg         [1:0] write_xgif_6, // Write Strobe for Interrupt Flag Register 6

  output reg         [1:0] write_xgif_5, // Write Strobe for Interrupt Flag Register 5

  output reg         [1:0] write_xgif_4, // Write Strobe for Interrupt Flag Register 4

  output reg         [1:0] write_xgif_3, // Write Strobe for Interrupt Flag Register 3

  output reg         [1:0] write_xgif_2, // Write Strobe for Interrupt Flag Register 2

  output reg         [1:0] write_xgif_1, // Write Strobe for Interrupt Flag Register 1

  output reg         [1:0] write_xgif_0, // Write Strobe for Interrupt Flag Register 0

  output reg               write_xgswt,  // Write Strobe for XGSWT register

  output reg               write_xgsem,  // Write Strobe for XGSEM register

  output reg               write_xgccr,  // Write Strobe for XGATE Condition Code Register

  output reg         [1:0] write_xgpc,   // Write Strobe for XGATE Program Counter

  output reg         [1:0] write_xgr7,   // Write Strobe for XGATE Data Register R7

  output reg         [1:0] write_xgr6,   // Write Strobe for XGATE Data Register R6

  output reg         [1:0] write_xgr5,   // Write Strobe for XGATE Data Register R5

  output reg         [1:0] write_xgr4,   // Write Strobe for XGATE Data Register R4

  output reg         [1:0] write_xgr3,   // Write Strobe for XGATE Data Register R3

  output reg         [1:0] write_xgr2,   // Write Strobe for XGATE Data Register R2

  output reg         [1:0] write_xgr1,   // Write Strobe for XGATE Data Register R1

  output reg         [1:0] write_irw_en_7, // Write Strobe for Interrupt Bypass Control Register 7

  output reg         [1:0] write_irw_en_6, // Write Strobe for Interrupt Bypass Control Register 6

  output reg         [1:0] write_irw_en_5, // Write Strobe for Interrupt Bypass Control Register 5

  output reg         [1:0] write_irw_en_4, // Write Strobe for Interrupt Bypass Control Register 4

  output reg         [1:0] write_irw_en_3, // Write Strobe for Interrupt Bypass Control Register 3

  output reg         [1:0] write_irw_en_2, // Write Strobe for Interrupt Bypass Control Register 2

  output reg         [1:0] write_irw_en_1, // Write Strobe for Interrupt Bypass Control Register 1

  output reg         [1:0] write_irw_en_0, // Write Strobe for Interrupt Bypass Control Register 0

  output                   async_rst_b,    //

  output                   sync_reset,     //

  input            [415:0] read_risc_regs, // status register bits for WISHBONE Read bus

  input            [127:1] irq_bypass      // IRQ status bits WISHBONE Read bus

  );

  // registers

  reg                bus_wait_state;  // Holdoff wbs_ack_o for one clock to add wait state

  reg         [5:0]  addr_latch;      // Capture WISHBONE Address 

  reg                write_reserv1;   // Dummy Reg decode for Reserved address

  reg                write_reserv2;   // Dummy Reg decode for Reserved address

  reg  [DWIDTH-1:0]  read_mux_irq;    // Psudo register for WISHBONE IRQ read data bus mux

  // Wires

  wire       module_sel;      // This module is selected for bus transaction

  wire       wbs_wacc;        // WISHBONE Write Strobe (Clock gating signal)

  wire       wbs_racc;        // WISHBONE Read Access (Clock gating signal)

  wire [5:0] address;         // Select either direct or latched address

  reg [DWIDTH-1:0] read_mux_risc;  // Pseudo regester for WISHBONE RISC read data bus mux 

  //

  // module body

  //

  // generate internal resets

  assign async_rst_b = arst_i ^ ARST_LVL;

  assign sync_reset  = wbs_rst_i;

  // generate wishbone signals

  assign module_sel  = wbs_cyc_i && wbs_stb_i;

  assign wbs_wacc    = module_sel && wbs_we_i && (wbs_ack_o || SINGLE_CYCLE);

  assign wbs_racc    = module_sel && !wbs_we_i;

  assign wbs_ack_o   = SINGLE_CYCLE ? module_sel : (bus_wait_state && module_sel);

  assign wbs_err_o   = !SINGLE_CYCLE && !module_sel && bus_wait_state;

  assign address     = SINGLE_CYCLE ? wbs_adr_i : addr_latch;

  assign wbs_dat_o   = read_mux_risc | read_mux_irq;

  // generate acknowledge output signal, By using register all accesses takes two cycles.

  //  Accesses in back to back clock cycles are not possible.

  always @(posedge wbs_clk_i or negedge async_rst_b)

    if (!async_rst_b)

      bus_wait_state <=  1'b0;

    else if (sync_reset)

      bus_wait_state <=  1'b0;

    else

      bus_wait_state <=  module_sel && !bus_wait_state;

  // Capture address in first cycle of WISHBONE Bus tranaction

  //  Only used when Wait states are enabled

  always @(posedge wbs_clk_i)

    if ( module_sel )                  // Clock gate for power saving

      addr_latch <= wbs_adr_i;

  // WISHBONE Read Data Mux for RISC status and control registers

  always @*

      case ({wbs_racc, address}) // synopsys parallel_case

        // 16 bit Bus, 16 bit Granularity

        7'b100_0000: read_mux_risc = read_risc_regs[ 15:  0];

        7'b100_0001: read_mux_risc = read_risc_regs[ 31: 16];

        7'b100_0010: read_mux_risc = read_risc_regs[ 47: 32];

        7'b100_0011: read_mux_risc = read_risc_regs[ 63: 48];

        7'b100_0100: read_mux_risc = read_risc_regs[ 79: 64];

        7'b100_0101: read_mux_risc = read_risc_regs[ 95: 80];

        7'b100_0110: read_mux_risc = read_risc_regs[111: 96];

        7'b100_0111: read_mux_risc = read_risc_regs[127:112];

        7'b100_1000: read_mux_risc = read_risc_regs[143:128];

        7'b100_1001: read_mux_risc = read_risc_regs[159:144];

        7'b100_1010: read_mux_risc = read_risc_regs[175:160];

        7'b100_1011: read_mux_risc = read_risc_regs[191:176];

        7'b100_1100: read_mux_risc = read_risc_regs[207:192];

        7'b100_1101: read_mux_risc = read_risc_regs[223:208];

        7'b100_1110: read_mux_risc = read_risc_regs[239:224];

        7'b100_1111: read_mux_risc = read_risc_regs[255:240];

        7'b101_0000: read_mux_risc = read_risc_regs[271:256];

        7'b101_0001: read_mux_risc = read_risc_regs[287:272];

        7'b101_0010: read_mux_risc = read_risc_regs[303:288];

        7'b101_0011: read_mux_risc = read_risc_regs[319:304];

        7'b101_0100: read_mux_risc = read_risc_regs[335:320];

        7'b101_0101: read_mux_risc = read_risc_regs[351:336];

        7'b101_0110: read_mux_risc = read_risc_regs[367:352];

        7'b101_0111: read_mux_risc = read_risc_regs[383:368];

        7'b101_1000: read_mux_risc = read_risc_regs[399:384];

        7'b101_1001: read_mux_risc = read_risc_regs[415:400];

        default: read_mux_risc = {DWIDTH{WB_RD_DEFAULT}};

      endcase

  // generate wishbone write register strobes for Xgate RISC 

  always @*

    begin

      write_reserv1 = 1'b0;

      write_reserv2 = 1'b0;

      write_xgmctl  = 1'b0;

      write_xgchid  = 1'b0;

      write_xgisp74 = 1'b0;

      write_xgisp30 = 1'b0;

      write_xgvbr  = 2'b00;

      write_xgif_7 = 2'b00;

      write_xgif_6 = 2'b00;

      write_xgif_5 = 2'b00;

      write_xgif_4 = 2'b00;

      write_xgif_3 = 2'b00;

      write_xgif_2 = 2'b00;

      write_xgif_1 = 2'b00;

      write_xgif_0 = 2'b00;

      write_xgswt  = 1'b0;

      write_xgsem  = 1'b0;

      write_xgccr  = 1'b0;

      write_xgpc   = 2'b00;

      write_xgr7   = 2'b00;

      write_xgr6   = 2'b00;

      write_xgr5   = 2'b00;

      write_xgr4   = 2'b00;

      write_xgr3   = 2'b00;

      write_xgr2   = 2'b00;

      write_xgr1   = 2'b00;

      if (wbs_wacc)

        case (address) // synopsys parallel_case

           // 16 bit Bus, 8 bit Granularity

           6'b00_0000 : write_xgmctl  = &wbs_sel_i;

           6'b00_0001 : write_xgchid  = wbs_sel_i[0];

           6'b00_0010 : write_xgisp74 = 1'b1;

           6'b00_0011 : write_xgisp30 = 1'b1;

           6'b00_0100 : write_xgvbr   = wbs_sel_i;

           6'b00_0101 : write_xgif_7  = wbs_sel_i;

           6'b00_0110 : write_xgif_6  = wbs_sel_i;

           6'b00_0111 : write_xgif_5  = wbs_sel_i;

           6'b00_1000 : write_xgif_4  = wbs_sel_i;

           6'b00_1001 : write_xgif_3  = wbs_sel_i;

           6'b00_1010 : write_xgif_2  = wbs_sel_i;

           6'b00_1011 : write_xgif_1  = wbs_sel_i;

           6'b00_1100 : write_xgif_0  = wbs_sel_i;

           6'b00_1101 : write_xgswt   = &wbs_sel_i;

           6'b00_1110 : write_xgsem   = &wbs_sel_i;

           6'b00_1111 : write_reserv1 = 1'b1;

           6'b01_0000 : write_xgccr   = wbs_sel_i[0];

           6'b01_0001 : write_xgpc    = wbs_sel_i;

           6'b01_0010 : write_reserv2 = 1'b1;

           6'b01_0011 : write_xgr1    = wbs_sel_i;

           6'b01_0100 : write_xgr2    = wbs_sel_i;

           6'b01_0101 : write_xgr3    = wbs_sel_i;

           6'b01_0110 : write_xgr4    = wbs_sel_i;

           6'b01_0111 : write_xgr5    = wbs_sel_i;

           6'b01_1000 : write_xgr6    = wbs_sel_i;

           6'b01_1001 : write_xgr7    = wbs_sel_i;

           default: ;

        endcase

    end

  // WISHBONE Read Data Mux for IRQ control registers

  always @*

      case ({wbs_racc, address}) // synopsys parallel_case

        // 16 bit Bus, 16 bit Granularity

        7'b110_0000: read_mux_irq = {irq_bypass[ 15:  1], 1'b0};

        7'b110_0001: read_mux_irq = irq_bypass[ 31: 16];

        7'b110_0010: read_mux_irq = irq_bypass[ 47: 32];

        7'b110_0011: read_mux_irq = irq_bypass[ 63: 48];

        7'b110_0100: read_mux_irq = irq_bypass[ 79: 64];

        7'b110_0101: read_mux_irq = irq_bypass[ 95: 80];

        7'b110_0110: read_mux_irq = irq_bypass[111: 96];

        7'b110_0111: read_mux_irq = irq_bypass[127:112];

        default: read_mux_irq = {DWIDTH{WB_RD_DEFAULT}};

      endcase

  // generate wishbone write register strobes for interrupt control

  always @*

    begin

      write_irw_en_7 = 2'b00;

      write_irw_en_6 = 2'b00;

      write_irw_en_5 = 2'b00;

      write_irw_en_4 = 2'b00;

      write_irw_en_3 = 2'b00;

      write_irw_en_2 = 2'b00;

      write_irw_en_1 = 2'b00;

      write_irw_en_0 = 2'b00;

      if (wbs_wacc)

        case (address) // synopsys parallel_case

           // 16 bit Bus, 8 bit Granularity

           6'b10_0000 : write_irw_en_0  = wbs_sel_i;

           6'b10_0001 : write_irw_en_1  = wbs_sel_i;

           6'b10_0010 : write_irw_en_2  = wbs_sel_i;

           6'b10_0011 : write_irw_en_3  = wbs_sel_i;

           6'b10_0100 : write_irw_en_4  = wbs_sel_i;

           6'b10_0101 : write_irw_en_5  = wbs_sel_i;

           6'b10_0110 : write_irw_en_6  = wbs_sel_i;

           6'b10_0111 : write_irw_en_7  = wbs_sel_i;

           default: ;

        endcase

    end

endmodule  // xgate_wbs_bus