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`timescale 1ns / 1ps

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

//        __

//   \\__/ o\    (C) 2013-2018  Robert Finch, Waterloo

//    \  __ /    All rights reserved.

//     \/_//     robfinch<remove>@finitron.ca

//       ||

//

// 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.                                      

//                                                                          

// This source file 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 General Public License for more details.                             

//                                                                          

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

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

//                                                                          

//

//              Encodes discrete interrupt request signals into five

//      bit code using a priority encoder.

//      

//      reg

//      0x00    - encoded request number (read / write)

//                      This register contains the number identifying

//                      the current requester in bits 0 to 4

//                      If there is no

//                      active request, then this number will be 

//                      zero.

//          bits 8 to 13 set the base number for the vector

//

//      0x04    - request enable (read / write)

//                      this register contains request enable bits

//                      for each request line. 1 = request

//                      enabled, 0 = request disabled. On reset this

//                      register is set to zero (disable all ints).

//                      bit zero is specially reserved for nmi

//

//      0x08   - write only

//                      this register disables the interrupt indicated

//                      by the low order five bits of the input data

//                      

//      0x0C    - write only

//                      this register enables the interrupt indicated

//                      by the low order five bits of the input data

//

//      0x10    - write only

//                      this register indicates which interrupt inputs are

//                      edge sensitive

//

//  0x14        - write only

//                      This register resets the edge sense circuitry

//                      indicated by the low order five bits of the input data.

//

//  0x80    - irq control for irq #0

//  0x84    - irq control for irq #1

//            bits 0 to 7  = cause code to issue

//            bits 8 to 11 = irq level to issue

//            bit 16 = irq enable

//            bit 17 = edge sensitivity

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

module FT64_pic

(

        input rst_i,            // reset

        input clk_i,            // system clock

        input cyc_i,

        input stb_i,

        output ack_o,       // controller is ready

        input wr_i,                     // write

        input [31:0] adr_i,      // address

        input [31:0] dat_i,

        output reg [31:0] dat_o,

        output vol_o,           // volatile register selected

        input i1, i2, i3, i4, i5, i6, i7,

                i8, i9, i10, i11, i12, i13, i14, i15,

                i16, i17, i18, i19, i20, i21, i22, i23,

                i24, i25, i26, i27, i28, i29, i30, i31,

        output [3:0] irqo,       // normally connected to the processor irq

        input nmii,             // nmi input connected to nmi requester

        output nmio,    // normally connected to the nmi of cpu

        output [6:0] causeo

);

parameter pIOAddress = 32'hFFDC_0F00;

reg [31:0] ie;           // interrupt enable register

reg rdy1;

reg [4:0] irqenc;

wire [31:0] i = {   i31,i30,i29,i28,i27,i26,i25,i24,i23,i22,i21,i20,i19,i18,i17,i16,

                    i15,i14,i13,i12,i11,i10,i9,i8,i7,i6,i5,i4,i3,i2,i1,nmii};

reg [31:0] ib;

reg [31:0] iedge;

reg [31:0] rste;

reg [31:0] es;

reg [5:0] cause_base;

reg [3:0] irq [0:31];

reg [7:0] cause [0:31];

integer n;

initial begin

        ie <= 32'h0;

        es <= 32'hFFFFFFFF;

        rste <= 32'h0;

        for (n = 0; n < 32; n = n + 1) begin

                cause[n] <= 8'h00;

                irq[n] <= 4'h8;

        end

end

wire cs = cyc_i && stb_i && adr_i[31:8]==pIOAddress[31:8];

assign vol_o = cs;

always @(posedge clk_i)

        rdy1 <= cs;

assign ack_o = cs ? (wr_i ? 1'b1 : rdy1) : 1'b0;

// write registers      

always @(posedge clk_i)

        if (rst_i) begin

                ie <= 32'h0;

                rste <= 32'h0;

        end

        else begin

                rste <= 32'h0;

                if (cs & wr_i) begin

                        casez (adr_i[7:2])

                        6'd0:    ;

                        6'd1:

                                begin

                                        ie[31:0] <= dat_i[31:0];

                                end

                        6'd2,6'd3:

                                ie[dat_i[4:0]] <= adr_i[2];

                        6'd4:   es <= dat_i[31:0];

                        6'd5:   rste[dat_i[4:0]] <= 1'b1;

                        6'b1?????:

                             begin

                                 cause[adr_i[6:2]] <= dat_i[7:0];

                                 irq[adr_i[6:2]] <= dat_i[11:8];

                                 ie[adr_i[6:2]] <= dat_i[16];

                                 es[adr_i[6:2]] <= dat_i[17];

                             end

                        endcase

                end

        end

// read registers

always @(posedge clk_i)

begin

        if (irqenc!=5'd0)

                $display("PIC: %d",irqenc);

        if (cs)

                casez (adr_i[7:2])

                6'd0:   dat_o <= {cause_base,3'd0} + irqenc;

                6'b1?????: dat_o <= {es[adr_i[6:2]],ie[adr_i[6:2]],4'b0,irq[adr_i[6:2]],cause[adr_i[6:2]]};

                default:        dat_o <= ie;

                endcase

        else

                dat_o <= 32'h0000;

end

assign irqo = (irqenc == 5'h0) ? 4'd0 : irq[irqenc];

assign causeo = (irqenc == 5'h0) ? 8'd0 : cause[irqenc];

assign nmio = nmii & ie[0];

// Edge detect circuit

always @(posedge clk_i)

begin

        for (n = 1; n < 32; n = n + 1)

        begin

                ib[n] <= i[n];

                if (i[n] & !ib[n]) iedge[n] <= 1'b1;

                if (rste[n]) iedge[n] <= 1'b0;

        end

end

// irq requests are latched on every rising clock edge to prevent

// misreads

// nmi is not encoded

always @(posedge clk_i)

begin

        irqenc <= 5'd0;

        for (n = 31; n > 0; n = n - 1)

                if (ie[n] & (es[n] ? iedge[n] : i[n])) irqenc <= n;

end

endmodule