source: sandbox/MultiChannelUSB/histogram16.v@ 167

module histogram16
        (
                input   wire                    clock, frame, reset,
                
                input   wire                    hst_good,
                input   wire    [13:0]  hst_data,

                input   wire                    bus_ssel, bus_wren,
                input   wire    [13:0]  bus_addr,
                input   wire    [15:0]  bus_mosi,

                output  wire    [15:0]  bus_miso,
                output  wire                    bus_busy
        );
        
        // signal declaration
        reg             [3:0]   int_case_reg, int_case_next;
        reg                             int_wren_reg, int_wren_next;
        reg             [13:0]  int_addr_reg, int_addr_next;
        reg             [15:0]  int_data_reg, int_data_next;

        reg             [13:0]  bus_addr_reg, bus_addr_next;
        reg             [15:0]  bus_miso_reg, bus_miso_next;

        reg                             bus_wren_reg, bus_wren_next;
        reg             [15:0]  bus_mosi_reg, bus_mosi_next;

        wire    [15:0]  q_a_wire;
        wire    [15:0]  q_b_wire;

        altsyncram #(
                .address_reg_b("CLOCK0"),
                .clock_enable_input_a("BYPASS"),
                .clock_enable_input_b("BYPASS"),
                .clock_enable_output_a("BYPASS"),
                .clock_enable_output_b("BYPASS"),
                .indata_reg_b("CLOCK0"),
                .intended_device_family("Cyclone III"),
                .lpm_type("altsyncram"),
                .numwords_a(16384),
                .numwords_b(16384),
                .operation_mode("BIDIR_DUAL_PORT"),
                .outdata_aclr_a("NONE"),
                .outdata_aclr_b("NONE"),
                .outdata_reg_a("CLOCK0"),
                .outdata_reg_b("CLOCK0"),
                .power_up_uninitialized("FALSE"),
                .read_during_write_mode_mixed_ports("OLD_DATA"),
                .read_during_write_mode_port_a("NEW_DATA_NO_NBE_READ"),
                .read_during_write_mode_port_b("NEW_DATA_NO_NBE_READ"),
                .widthad_a(14),
                .widthad_b(14),
                .width_a(16),
                .width_b(16),
                .width_byteena_a(1),
                .width_byteena_b(1),
                .wrcontrol_wraddress_reg_b("CLOCK0")) hst_ram_unit(
                .wren_a(int_wren_reg),
                .clock0(clock),
                .wren_b(bus_wren_reg),
                .address_a(int_addr_reg),
                .address_b(bus_addr_reg),
                .data_a(int_data_reg),
                .data_b(bus_mosi_reg),
                .q_a(q_a_wire),
                .q_b(q_b_wire),
                .aclr0(1'b0),
                .aclr1(1'b0),
                .addressstall_a(1'b0),
                .addressstall_b(1'b0),
                .byteena_a(1'b1),
                .byteena_b(1'b1),
                .clock1(1'b1),
                .clocken0(1'b1),
                .clocken1(1'b1),
                .clocken2(1'b1),
                .clocken3(1'b1),
                .eccstatus(),
                .rden_a(1'b1),
                .rden_b(1'b1));

        // body
        always @(posedge clock)
        begin
                if (reset)
        begin
                        int_wren_reg <= 1'b1;
                        int_addr_reg <= 14'd0;
                        int_data_reg <= 16'd0;
                        int_case_reg <= 4'b0;
                        bus_addr_reg <= 14'd0;
                        bus_miso_reg <= 16'd0;
                        bus_wren_reg <= 1'b0;
                        bus_mosi_reg <= 16'd0;
                end
                else
                begin
                        int_wren_reg <= int_wren_next;
                        int_addr_reg <= int_addr_next;
                        int_data_reg <= int_data_next;
                        int_case_reg <= int_case_next;
                        bus_addr_reg <= bus_addr_next;
                        bus_miso_reg <= bus_miso_next;
                        bus_wren_reg <= bus_wren_next;
                        bus_mosi_reg <= bus_mosi_next;
                end             
        end

        always @*
        begin
                bus_addr_next = bus_addr_reg;
                bus_miso_next = bus_miso_reg;

                bus_wren_next = 1'b0;
                bus_mosi_next = bus_mosi_reg;

                if (bus_ssel)
                begin
                        bus_miso_next = q_b_wire;       
                        bus_addr_next = bus_addr;
                        bus_wren_next = bus_wren;       
                        if (bus_wren)
                        begin
                                bus_mosi_next = bus_mosi;
                        end
                end
        end

        always @*
        begin
                int_wren_next = int_wren_reg;
                int_addr_next = int_addr_reg;
                int_data_next = int_data_reg;
                int_case_next = int_case_reg;

                case (int_case_reg)
                                                
                        0:
                        begin
                                // write zeros
                                int_addr_next = int_addr_reg + 14'd1;
                                if (&int_addr_reg)
                                begin
                                        int_wren_next = 1'b0;
                                        int_case_next = 4'd1;
                                end
                        end     

                        1:
                        begin
                                int_wren_next = 1'b0;
/*
                                if (&int_data_reg)
                                begin
                                        int_case_next = 4'd0;
                                end
                                else if (frame & hst_good)
*/
                                if (frame & hst_good)
                                begin
                                        int_addr_next = hst_data;
                                        int_case_next = 4'd2;
                                end
                        end

                        2:
                        begin
                                int_case_next = 4'd3;
                        end

                        3:
                        begin
                                int_case_next = 4'd4;
                        end

                        4:
                        begin
                                int_case_next = 4'd1;
                                if (~&q_a_wire)
                                begin
                                        int_wren_next = 1'b1;
                                        int_data_next = q_a_wire + 16'd1;
                                end
                        end

                        default:
                        begin
                                int_wren_next = 1'b0;
                                int_addr_next = 14'd0;
                                int_data_next = 16'd0;
                                int_case_next = 4'd0;
                        end
                endcase
        end

        // output logic
        assign  bus_miso = bus_miso_reg;
        assign  bus_busy = 1'b0;
endmodule