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/*

 * Copyright 2010, Aleksander Osman, alfik@poczta.fm. All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without modification, are

 * permitted provided that the following conditions are met:

 *

 *  1. Redistributions of source code must retain the above copyright notice, this list of

 *     conditions and the following disclaimer.

 *

 *  2. Redistributions in binary form must reproduce the above copyright notice, this list

 *     of conditions and the following disclaimer in the documentation and/or other materials

 *     provided with the distribution.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 THE AUTHOR OR

 * CONTRIBUTORS 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.

 */

/*! \file

 * \brief OCS floppy implementation with WISHBONE master and slave interface.

 */

/*! \brief \copybrief ocs_floppy.v

List of floppy registers:

\verbatim

Implemented:

     [SERDATR   *018  R   P       Serial port data and status read              read not implemented here]

    DSKBYTR     *01A  R   P       Disk data byte and status read                read not implemented here

    DSKPTH    + *020  W   A( E )  Disk pointer (high 3 bits, 5 bits if ECS)

    DSKPTL    + *022  W   A       Disk pointer (low 15 bits)

    DSKLEN      *024  W   P       Disk length

    DSKDAT    & *026  W   P       Disk DMA data write

        [not used 07C]

    DSKSYNC     ~07E  W   P       Disk sync pattern register for disk read

Not implemented:

    DSKDATR   & *008  ER  P       Disk data early read (dummy address)          not implemented

     [JOY0DAT   *00A  R   D       Joystick-mouse 0 data (vert,horiz)            read not implemented here]

\endverbatim

*/

module ocs_floppy(

    //% \name Clock and reset

    //% @{

    input               CLK_I,

    input               reset_n,

    //% @}

    //% \name On-Screen-Display floppy management interface

    //% @{

    input               floppy_inserted,

    input [31:0]        floppy_sector,

    input               floppy_write_enabled,

    output reg          floppy_error,

    //% @}

    //% \name WISHBONE master

    //% @{

    output reg          CYC_O,

    output reg          STB_O,

    output reg          WE_O,

    output reg [31:2]   ADR_O,

    output reg [3:0]    SEL_O,

    output reg [31:0]   master_DAT_O,

    input [31:0]        master_DAT_I,

    input               ACK_I,

    //% @}

    //% \name WISHBONE slave for OCS registers

    //% @{

    input               CYC_I,

    input               STB_I,

    input               WE_I,

    input [8:2]         ADR_I,

    input [3:0]         SEL_I,

    input [31:0]        slave_DAT_I,

    output reg          ACK_O,

    //% @}

    //% \name WISHBONE slave for floppy buffer

    //% @{

    input               buffer_CYC_I,

    input               buffer_STB_I,

    input               buffer_WE_I,

    input [13:2]        buffer_ADR_I,

    input [3:0]         buffer_SEL_I,

    input [31:0]        buffer_DAT_I,

    output [31:0]       buffer_DAT_O,

    output reg          buffer_ACK_O,

    //% @}

    //% \name Not aligned register access on a 32-bit WISHBONE bus

    //% @{

        // DSKBYTR read not implemented here

    input               na_dskbytr_read,

    output [15:0]       na_dskbytr,

    //% @}

    //% \name Internal OCS ports

    //% @{

    input               line_start,

    input [10:0]        dma_con,

    input [14:0]        adk_con,

    output reg          floppy_syn_irq,

    output reg          floppy_blk_irq,

    //% @}

    //% \name Floppy CIA interface

    //% @{

    output              fl_rdy_n,

    output              fl_tk0_n,

    output              fl_wpro_n,

    output              fl_chng_n,

    output              fl_index_n,

    input               fl_mtr_n,

    input [3:0]         fl_sel_n,

    input               fl_side_n,

    input               fl_dir,

    input               fl_step_n,

    //% @}

    //% \name Debug signals

    //% @{

    output [7:0]        debug_floppy,

    output [7:0]        debug_track

    //% @}

);

reg [33:0]  mfm_encoder;

reg [31:0]  checksum;

reg [3:0]   sector;

reg         last_checksum_bit;

reg [31:0]  first_long_word;

wire [63:0] mfm_output = {

    ~mfm_encoder[33] & ~mfm_encoder[31], mfm_encoder[31], ~mfm_encoder[31] & ~mfm_encoder[29], mfm_encoder[29],

    ~mfm_encoder[29] & ~mfm_encoder[27], mfm_encoder[27], ~mfm_encoder[27] & ~mfm_encoder[25], mfm_encoder[25],

    ~mfm_encoder[25] & ~mfm_encoder[23], mfm_encoder[23], ~mfm_encoder[23] & ~mfm_encoder[21], mfm_encoder[21],

    ~mfm_encoder[21] & ~mfm_encoder[19], mfm_encoder[19], ~mfm_encoder[19] & ~mfm_encoder[17], mfm_encoder[17],

    ~mfm_encoder[17] & ~mfm_encoder[15], mfm_encoder[15], ~mfm_encoder[15] & ~mfm_encoder[13], mfm_encoder[13],

    ~mfm_encoder[13] & ~mfm_encoder[11], mfm_encoder[11], ~mfm_encoder[11] & ~mfm_encoder[9],  mfm_encoder[9],

    ~mfm_encoder[9]  & ~mfm_encoder[7],  mfm_encoder[7],  ~mfm_encoder[7]  & ~mfm_encoder[5],  mfm_encoder[5],

    ~mfm_encoder[5]  & ~mfm_encoder[3],  mfm_encoder[3],  ~mfm_encoder[3]  & ~mfm_encoder[1],  mfm_encoder[1],

    ~mfm_encoder[32] & ~mfm_encoder[30], mfm_encoder[30], ~mfm_encoder[30] & ~mfm_encoder[28], mfm_encoder[28],

    ~mfm_encoder[28] & ~mfm_encoder[26], mfm_encoder[26], ~mfm_encoder[26] & ~mfm_encoder[24], mfm_encoder[24],

    ~mfm_encoder[24] & ~mfm_encoder[22], mfm_encoder[22], ~mfm_encoder[22] & ~mfm_encoder[20], mfm_encoder[20],

    ~mfm_encoder[20] & ~mfm_encoder[18], mfm_encoder[18], ~mfm_encoder[18] & ~mfm_encoder[16], mfm_encoder[16],

    ~mfm_encoder[16] & ~mfm_encoder[14], mfm_encoder[14], ~mfm_encoder[14] & ~mfm_encoder[12], mfm_encoder[12],

    ~mfm_encoder[12] & ~mfm_encoder[10], mfm_encoder[10], ~mfm_encoder[10] & ~mfm_encoder[8],  mfm_encoder[8],

    ~mfm_encoder[8]  & ~mfm_encoder[6],  mfm_encoder[6],  ~mfm_encoder[6]  & ~mfm_encoder[4],  mfm_encoder[4],

    ~mfm_encoder[4]  & ~mfm_encoder[2],  mfm_encoder[2],  ~mfm_encoder[2]  & ~mfm_encoder[0],  mfm_encoder[0]

};

wire [31:0] header =

    { 8'hFF, {track, 1'b0} + {7'b0, ~last_fl_side_n}, {4'b0, sector}, 8'd11 - {4'b0, sector} };

wire [31:0] masked_checksum = checksum & 32'h55555555;

reg [47:0] output_shift;

reg [15:0] output_first_word;

reg [5:0] output_line_cnt;

reg [5:0] last_output_line_cnt;

reg [4:0] output_shift_cnt;

wire output_shifting = (last_output_line_cnt != 6'd0);

wire output_shifted = (last_dsksync_halt == 1'b0 && last_output_line_cnt != 6'd0 && output_line_cnt == 6'd0);

wire output_index = (last_buffer_addr == 12'd3124 && buffer_addr == 12'd0);

wire write_sector_ready = (buffer_addr == 12'd127);

wire [31:0] output_long_word = { output_first_word, output_shift[47:32] };

//*********************************** FLOPPY BUFFER start

reg [11:0] buffer_addr;

reg [11:0] last_buffer_addr;

reg [8:0] buffer_counter;

reg last_buffer_ACK_O;

wire buffer_write_cycle =

    (buffer_CYC_I == 1'b1 && buffer_STB_I == 1'b1 && buffer_WE_I == 1'b1 && buffer_SEL_I == 4'b1111 && buffer_ACK_O == 1'b0);

wire buffer_read_cycle =

    (buffer_CYC_I == 1'b1 && buffer_STB_I == 1'b1 && buffer_WE_I == 1'b0 && buffer_SEL_I == 4'b1111 && buffer_ACK_O == 1'b0);

wire buffer_wren =

    (enable_write == 1'b1)?                                                         1'b1 :

    (buffer_counter >= 9'd1 && buffer_counter <= 9'd14)?                            1'b1 :

    (buffer_counter >= 9'd16 && buffer_counter <= 9'd271 && (buffer_ACK_O == 1'b1 || last_buffer_ACK_O == 1'b1))?  1'b1 :

    (buffer_counter >= 9'd272 && buffer_counter <= 9'd275)?                         1'b1 :

    1'b0;

wire [31:0] buffer_data =

    (enable_write == 1'b1)?                                 master_DAT_O :

    (buffer_counter == 9'd1)?                               32'hAAAAAAAA :

    (buffer_counter == 9'd2)?                               32'h44894489 :

    // insert header, insert header checksum

    (buffer_counter == 9'd3 || buffer_counter == 9'd13)?    mfm_output[63:32] :

    (buffer_counter == 9'd4 || buffer_counter == 9'd14)?    mfm_output[31:0] :

    (buffer_counter == 9'd5)?                               { ~mfm_encoder[0], 1'b0, 2'b10, 28'hAAAAAAA } :

    (buffer_counter <= 9'd14)?                              32'hAAAAAAAA :

    // insert data, count data checksum

    (buffer_counter >= 9'd16 && buffer_counter <= 9'd270 && buffer_counter[0] == 1'b0)?

                                                            mfm_output[63:32] :

    (buffer_counter >= 9'd17 && buffer_counter <= 9'd271 && buffer_counter[0] == 1'b1)?

                                                            mfm_output[31:0] :

    // fix first and middle bit

    (buffer_counter == 9'd272 || buffer_counter == 9'd274)? mfm_output[63:32] :

    // write checksum

    (buffer_counter == 9'd273 || buffer_counter == 9'd275)? mfm_output[31:0] :

                                                            32'd0;

wire [31:0] buffer_q;

altsyncram buffer_ram_inst(

    .clock0     (CLK_I),

    .address_a  (buffer_addr),

    .wren_a     (buffer_wren),

    .data_a     (buffer_data),

    .q_a        (buffer_q),

    .clock1     (CLK_I),

    .address_b  (buffer_ADR_I),

    .q_b        (buffer_DAT_O)

);

defparam

    buffer_ram_inst.operation_mode  = "BIDIR_DUAL_PORT",

    buffer_ram_inst.width_a         = 32,

    buffer_ram_inst.widthad_a       = 12,

    buffer_ram_inst.width_b         = 32,

    buffer_ram_inst.widthad_b       = 12,

    buffer_ram_inst.init_file       = "ocs_floppy.mif";

/*

    buffer_counter

    15->16:     load mfm A, load addr A

    16->17:     store A, load addr A+128

    17->18:     load mfm A+1, store A+128, load addr A+1

    18->19:     store A+1, load addr A+129

    ......

    269->270:   load mfm A+127, store A+254, load addr A+127

    270->271:   store A+127, load addr A+255

    271->272:   store A+255

*/

always @(posedge CLK_I or negedge reset_n) begin

    if(reset_n == 1'b0) begin

        buffer_addr             <= 12'd0;

        last_buffer_addr        <= 12'd0;

        buffer_counter          <= 9'd0;

        mfm_encoder             <= 34'd0;

        checksum                <= 32'd0;

        sector                  <= 4'd0;

        last_checksum_bit       <= 1'b0;

        first_long_word         <= 32'd0;

        buffer_ACK_O            <= 1'b0;

        last_buffer_ACK_O       <= 1'b0;

        output_shift            <= 48'd0;

        output_first_word       <= 16'd0;

        output_line_cnt         <= 6'd0;

        last_output_line_cnt    <= 6'd0;

        output_shift_cnt        <= 5'd0;

    end

    else begin

        last_buffer_ACK_O <= buffer_ACK_O;

        if(buffer_write_cycle == 1'b1 || buffer_read_cycle == 1'b1) buffer_ACK_O <= 1'b1;

        else                                                        buffer_ACK_O <= 1'b0;

        if(buffer_counter >= 9'd3 && buffer_counter <= 9'd12)

            checksum <= checksum ^ buffer_data;

        else if(buffer_counter == 9'd14)

            checksum <= 32'd0;

        else if(buffer_counter >= 9'd16 && buffer_counter <= 9'd271 && buffer_wren == 1'b1)

            checksum <= checksum ^ buffer_data;

        else if(buffer_counter == 9'd275)

            checksum <= 32'd0;

        if(buffer_counter == 9'd14)     last_checksum_bit <= buffer_data[0];

        if(buffer_counter == 9'd15)     first_long_word <= buffer_DAT_I;

        if(buffer_counter == 9'd275 && sector < 4'd10)  sector <= sector + 4'd1;

        else if(buffer_counter == 9'd275)               sector <= 4'd0;

        if(start_read == 1'b1) begin

            buffer_counter <= 9'd1;

            buffer_addr <= 12'd0;

            checksum <= 32'd0;

            sector <= 4'd0;

        end

        if(buffer_counter >= 9'd1 && buffer_counter <= 9'd14)

            buffer_counter <= buffer_counter + 9'd1;

        else if(buffer_counter >= 9'd15 && buffer_counter <= 9'd269 && buffer_counter[0] == 1'b1 && buffer_write_cycle == 1'b1)

            buffer_counter <= buffer_counter + 9'd1;

        else if(buffer_counter >= 9'd16 && buffer_counter <= 9'd270 && buffer_counter[0] == 1'b0)

            buffer_counter <= buffer_counter + 9'd1;

        else if(buffer_counter >= 9'd271 && buffer_counter <= 9'd274)

            buffer_counter <= buffer_counter + 9'd1;

        else if(buffer_counter == 9'd275 && sector < 4'd10)

            buffer_counter <= 9'd1;

        else if(buffer_counter == 9'd275)

            buffer_counter <= 9'd0;

        if(buffer_counter >= 9'd1 && buffer_counter <= 9'd13)

            buffer_addr <= buffer_addr + 12'd1;

        // skip data checksum

        else if(buffer_counter == 9'd14)

            buffer_addr <= buffer_addr + 12'd3;

        else if(buffer_counter >= 9'd17 && buffer_counter <= 9'd269 && buffer_counter[0] == 1'b1 && buffer_write_cycle == 1'b1)

            buffer_addr <= buffer_addr - 12'd128 + 12'd1;

        else if(buffer_counter >= 9'd16 && buffer_counter <= 9'd270 && buffer_counter[0] == 1'b0)

            buffer_addr <= buffer_addr + 12'd128;

        else if(buffer_counter == 9'd271)

            buffer_addr <= buffer_addr - 12'd256 + 12'd1;

        else if(buffer_counter == 9'd272)

            buffer_addr <= buffer_addr + 12'd128;

        else if(buffer_counter == 9'd273)

            buffer_addr <= buffer_addr - 12'd128 - 12'd2;

        else if(buffer_counter == 9'd274)

            buffer_addr <= buffer_addr + 12'd1;

        else if(buffer_counter == 9'd275 && sector < 4'd10)

            buffer_addr <= buffer_addr + 12'd1 + 12'd256;

        else if(buffer_counter == 9'd275)

            buffer_addr <= 12'd0;

        if(buffer_counter == 9'd2)

            mfm_encoder <= { 1'b1, header[1], header[31:0] };

        // checksum

        else if(buffer_counter == 9'd12)

            mfm_encoder <= { 1'b0, masked_checksum[1], masked_checksum[31:0] };

        else if(buffer_counter == 9'd15 && buffer_write_cycle == 1'b1)

            mfm_encoder <= { 1'b1, 1'b1, buffer_DAT_I };

        else if(buffer_counter >= 9'd17 && buffer_counter <= 9'd269 && buffer_counter[0] == 1'b1 && buffer_write_cycle == 1'b1)

            mfm_encoder <= { mfm_encoder[1], mfm_encoder[0], buffer_DAT_I};

        else if(buffer_counter == 9'd271)

            mfm_encoder <= { checksum[0]^buffer_data[0], mfm_encoder[1], first_long_word };

        else if(buffer_counter == 9'd273)

            mfm_encoder <= { last_checksum_bit, masked_checksum[1], masked_checksum[31:0] };

        last_output_line_cnt <= output_line_cnt;

        last_buffer_addr <= buffer_addr;

        if(output_line_cnt == 6'd16) output_first_word[15:0] <= output_shift[47:32];

        //if(output_shifted) $display("%08x ", output_long_word);

        // read mfm data

        if(buffer_counter == 9'd0 && start_read == 1'b0 && active_write == 1'b0) begin

            if(output_line_cnt != 6'd0 && dsksync_halt == 1'b0) begin

                if(output_shift_cnt == 5'd0)    output_shift <= { output_shift[46:32], buffer_q, 1'b0 };

                else                            output_shift <= { output_shift[46:0], 1'b0 };

                if(output_shift_cnt == 5'd0) begin

                    if(buffer_addr == 12'd3124) buffer_addr <= 12'd0;

                    else                        buffer_addr <= buffer_addr + 12'd1;

                end

                output_shift_cnt <= output_shift_cnt - 5'd1;

            end

            if(output_line_cnt != 6'd0 && dsksync_halt == 1'b1) begin

                output_line_cnt <= 6'd0;

            end

            else if(output_line_cnt != 6'd0) begin

                output_line_cnt <= output_line_cnt - 6'd1;

            end

            else if(line_start == 1'b1) begin

                output_line_cnt <= 6'd32;

            end

        end

        // write data

        else if(buffer_counter == 9'd0 && start_read == 1'b0 && active_write == 1'b1) begin

            if(start_write == 1'b1)         buffer_addr <= 12'd0;

            else if(enable_write == 1'b1)   buffer_addr <= buffer_addr + 12'd1;

        end

        else begin

            output_shift_cnt <= 5'd0;

            output_line_cnt <= 6'd0;

        end

    end

end

//*********************************** FLOPPY BUFFER end

assign debug_track = { 1'b0, track };

assign debug_floppy = { last_fl_side_n, adk_con[10], dma_active, state > 4'd7, state };

assign fl_tk0_n     = (fl_sel_n == 4'b1110 && track == 7'd0)? 1'b0 : 1'b1;

assign fl_wpro_n    = (floppy_inserted == 1'b1 && fl_sel_n == 4'b1110)? floppy_write_enabled : 1'b1;

//id bit = 1 for internal drive

assign fl_rdy_n     = (floppy_inserted == 1'b1 && fl_sel_n == 4'b1110 && motor_spinup_delay == 15'd32767)? 1'b0 : 1'b1;

assign fl_chng_n    = (fl_sel_n == 4'b1110)? reg_fl_chng_n : 1'b1;

assign fl_index_n   = (fl_sel_n == 4'b1110)? reg_fl_index_n : 1'b1;

reg [6:0] track;

reg last_fl_step_n;

reg floppy_pos_changed;

reg [3:0] last_fl_sel_n;

reg last_fl_side_n;

reg reg_fl_chng_n;

reg reg_fl_index_n;

reg reg_fl_mtr_n;

reg [14:0] motor_spinup_delay;

reg [31:0] dskptr;

reg [15:0] dsklen;

reg [15:0] dsksync;

reg last_dma_secondary;

reg dma_started;

reg [31:0] mfm_decoder;

wire dma_active;

assign dma_active =

    last_dma_secondary == 1'b1 && dsklen[15] == 1'b1 && dma_con[9] == 1'b1 && dma_con[4] == 1'b1 && dsklen[13:0] != 14'd0;

reg [5:0] byte_dsksync;

reg [2:0] byte_counter;

assign na_dskbytr = { byte_counter != 3'd0, dma_active, dsklen[14], byte_dsksync != 6'd0,

    (byte_counter == 3'd1)? output_long_word[31:24] :

    (byte_counter == 3'd2)? output_long_word[23:16] :

    (byte_counter == 3'd3)? output_long_word[15:8] :

    output_long_word[7:0]

};

reg [3:0] substate;

reg [3:0] last_substate;

reg [3:0] state;

reg [3:0] last_state;

parameter [3:0]

    S_IDLE              = 4'd0,

    S_READ_FROM_SD      = 4'd1,

    S_READ_READY_0      = 4'd2,

    S_READ_READY_1      = 4'd3,

    S_WRITE_CONVERT_0   = 4'd4,

    S_WRITE_CONVERT_1   = 4'd5,

    S_WRITE_CONVERT_2   = 4'd6,

    S_WRITE_TO_SD       = 4'd7;

// byte position:   track*2*11*512  + side*11*512

// sector position: track*2*11      + side*11       = track*2*(8+2+1) + side*(8+2+1) = track*(16+4+2) + side*(8+2+1)

wire [31:0] sd_track_address;

assign sd_track_address =

    floppy_sector +

    { 21'b0, track, 4'b0 } +

    { 23'b0, track, 2'b0 } +

    { 24'b0, track, 1'b0 } +

    { 28'b0, ~last_fl_side_n, 3'b0 } +

    { 30'b0, ~last_fl_side_n, 1'b0 } +

    { 31'b0, ~last_fl_side_n };

wire [15:0] mfm_decoder_odd_30_16 = {

    master_DAT_I[30], 1'b0, master_DAT_I[28], 1'b0,

    master_DAT_I[26], 1'b0, master_DAT_I[24], 1'b0,

    master_DAT_I[22], 1'b0, master_DAT_I[20], 1'b0,

    master_DAT_I[18], 1'b0, master_DAT_I[16], 1'b0

};

wire [15:0] mfm_decoder_odd_14_0 = {

    master_DAT_I[14], 1'b0, master_DAT_I[12], 1'b0,

    master_DAT_I[10], 1'b0, master_DAT_I[8], 1'b0,

    master_DAT_I[6], 1'b0, master_DAT_I[4], 1'b0,

    master_DAT_I[2], 1'b0, master_DAT_I[0], 1'b0

};

wire [15:0] mfm_decoder_even_30_16 = {

    1'b0, master_DAT_I[30], 1'b0, master_DAT_I[28],

    1'b0, master_DAT_I[26], 1'b0, master_DAT_I[24],

    1'b0, master_DAT_I[22], 1'b0, master_DAT_I[20],

    1'b0, master_DAT_I[18], 1'b0, master_DAT_I[16]

};

wire [15:0] mfm_decoder_even_14_0 = {

    1'b0, master_DAT_I[14], 1'b0, master_DAT_I[12],

    1'b0, master_DAT_I[10], 1'b0, master_DAT_I[8],

    1'b0, master_DAT_I[6], 1'b0, master_DAT_I[4],

    1'b0, master_DAT_I[2], 1'b0, master_DAT_I[0]

};

wire [31:0] dskptr_sum =

    (substate == 4'd0)? dskptr + 32'd0 :

    (substate == 4'd1)? dskptr + 32'd2 :

    (substate == 4'd2)? dskptr + 32'd512 :

    dskptr + 32'd514;

wire start_read     = (last_state == S_IDLE && state == S_READ_FROM_SD);

wire start_write    = (last_state == S_WRITE_CONVERT_1 && state == S_WRITE_CONVERT_2);

wire active_write   = (state == S_WRITE_CONVERT_2 || state == S_WRITE_TO_SD);

wire enable_write   = (last_state == S_WRITE_CONVERT_2 && last_substate == 4'd3 && substate == 4'd0);

wire dsksync_halt   = (output_shift[47:32] == dsksync && dma_started == 1'b0 && output_shifting == 1'b1 && dma_active == 1'b1 && dsklen[14] == 1'b0);

reg last_dsksync_halt;

always @(posedge CLK_I or negedge reset_n) begin

    if(reset_n == 1'b0) begin

        floppy_error <= 1'b0;

        CYC_O <= 1'b0;

        STB_O <= 1'b0;

        WE_O <= 1'b0;

        ADR_O <= 30'd0;

        SEL_O <= 4'b0000;

        master_DAT_O <= 32'd0;

        ACK_O <= 1'b0;

        floppy_syn_irq <= 1'b0;

        floppy_blk_irq <= 1'b0;