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[/] [eco32/] [trunk/] [fpga/] [mc/] [src/] [dsk/] [atactrl.v] - Blame information for rev 323

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//
// atactrl.v -- parallel ATA controller
//
 
 
`timescale 1ns/10ps
`default_nettype none
 
 
`define ADDR_ALTERNATE_STATUS   4'b0110
`define ADDR_DEVICE_CONTROL     4'b0110
`define ADDR_DEVICE_ADDRESS     4'b0111
`define ADDR_DATA               4'b1000
`define ADDR_ERROR              4'b1001
`define ADDR_FEATURES           4'b1001
`define ADDR_SECTOR_COUNT       4'b1010
`define ADDR_LBA0               4'b1011
`define ADDR_LBA1               4'b1100
`define ADDR_LBA2               4'b1101
`define ADDR_LBA3_DRV           4'b1110
`define ADDR_STATUS             4'b1111
`define ADDR_COMMAND            4'b1111
 
 
module ata_ctrl (
        input clk, reset,
 
        input bus_en, bus_wr,
        input [19:2] bus_addr,
        input [31:0] bus_din,
        output [31:0] bus_dout,
        output bus_wait,
        output bus_irq,
 
        inout [15:0] ata_d,
        output [2:0] ata_a,
        output ata_cs0_n, ata_cs1_n,
        output ata_dior_n, ata_diow_n,
        input ata_intrq,
        input ata_dmarq,
        output ata_dmack_n,
        input ata_iordy
);
 
// --- ATA IRQ line debouncing
reg debounced_ata_intrq, prev_ata_intrq;
reg [3:0] ata_intrq_debounce_counter;
 
// --- disk buffer
 
// interface to the bus
wire buffer_bus_wait;
wire [31:0] buffer_bus_dout;
 
// interface to the state machine
wire buffer_ata_write;
wire [11:1] buffer_ata_addr;
wire [15:0] buffer_ata_din;
wire [15:0] buffer_ata_dout;
wire buffer_bus_addressed;
wire buffer_bus_write;
reg buffer_bus_second_cycle;
 
ata_buffer ata_buffer_1(
    .clk (clk),
    .bus_write (buffer_bus_write),
    .bus_addr (bus_addr [11:2]),
    .bus_din (bus_din),
    .bus_dout (buffer_bus_dout),
    .ata_write (buffer_ata_write),
    .ata_addr (buffer_ata_addr),
    .ata_din (buffer_ata_din),
    .ata_dout (buffer_ata_dout)
);
 
assign buffer_bus_addressed = bus_addr [19];
assign buffer_bus_wait = bus_en & !buffer_bus_second_cycle;
assign buffer_bus_write = bus_en & bus_wr &
    buffer_bus_addressed & !buffer_bus_second_cycle;
 
// --- control registers
 
// interface to the bus
wire control_bus_wait;
wire [31:0] control_bus_dout;
 
// interface to the state machine
reg [31:0] capacity;
reg [27:0] requestedSectorAddress;
reg [3:0] requestedSectorCount;
wire commandUnlocked;
reg enableInterrupts, requestedWrite, errorOutput;
reg operationFinished, diskInitialized;
wire control_bus_addressed;
 
assign control_bus_addressed = !bus_addr[19];
assign control_bus_wait = 0;
assign control_bus_dout =
        (bus_addr [3:2] == 2'b00) ? {ata_dmarq, 25'd0,
                diskInitialized, operationFinished,
                errorOutput, requestedWrite,
                enableInterrupts, 1'b0} :
        (bus_addr [3:2] == 2'b01) ? { 28'd0, requestedSectorCount } :
        (bus_addr [3:2] == 2'b10) ? { 4'd0, requestedSectorAddress } :
        capacity;
 
// --- ATA IO component
 
reg io_en, io_write;
wire io_wait;
reg [3:0] io_addr;
reg [15:0] io_data_out;
wire [15:0] io_data_in;
 
assign ata_dmack_n = 1'b1;
ata_io io (
        .clk(clk),
        .reset(reset),
        .bus_en(io_en),
        .bus_wr(io_write),
        .bus_addr(io_addr),
        .bus_din(io_data_out),
        .bus_dout(io_data_in),
        .bus_wait(io_wait),
        .ata_d(ata_d),
        .ata_a(ata_a),
        .ata_cs0_n(ata_cs0_n),
        .ata_cs1_n(ata_cs1_n),
        .ata_dior_n(ata_dior_n),
        .ata_diow_n(ata_diow_n),
        .ata_iordy(ata_iordy)
);
 
// --- bus interface
 
assign bus_dout = bus_addr [19] ? buffer_bus_dout : control_bus_dout;
assign bus_wait = bus_addr [19] ? buffer_bus_wait : control_bus_wait;
assign bus_irq = enableInterrupts & operationFinished;
 
// --- state machine
 
reg [4:0] state;
reg [7:0] aux_counter;
reg [2:0] sector_counter;
/*
    STARTUP DEBUG LOGGING
reg [15:0] debugTimer;
*/
 
wire startBit;
assign commandUnlocked = (state == 5'd8);
assign startBit = bus_en & bus_wr &
    (!bus_addr [19]) & (bus_addr [3:2] == 2'b00) &
    bus_din [0];
 
assign buffer_ata_write = (state == 5'd16) & (!io_wait);
assign buffer_ata_addr = {sector_counter, aux_counter [7:0]};
assign buffer_ata_din = io_data_in;
 
always @(posedge clk) begin
    if (reset) begin
 
        prev_ata_intrq <= 1'b0;
        debounced_ata_intrq <= 1'b0;
        ata_intrq_debounce_counter <= 4'b0;
 
        buffer_bus_second_cycle <= 1'b0;
 
        capacity <= 32'd0;
        requestedSectorAddress <= 32'd0;
        requestedSectorCount <= 4'b0000;
 
        enableInterrupts <= 1'b0;
        requestedWrite <= 1'b0;
        errorOutput <= 1'b0;
        operationFinished <= 1'b0;
        diskInitialized <= 1'b0;
 
        io_en <= 1'b0;
        io_write <= 1'b0;
        io_addr <= 32'd0;
        io_data_out <= 16'd0;
 
        state <= 5'd0;
        aux_counter <= 8'd0;
        sector_counter <= 3'd0;
 
/*
    STARTUP DEBUG LOGGING
        debugTimer <= 16'd0;
*/
 
    end else begin
 
        if (ata_intrq == prev_ata_intrq) begin
            if (ata_intrq_debounce_counter == 4'd0) begin
                debounced_ata_intrq <= ata_intrq;
            end else begin
                ata_intrq_debounce_counter <= ata_intrq_debounce_counter - 1;
            end
        end else begin
            ata_intrq_debounce_counter <= 4'd10;
        end
        prev_ata_intrq <= ata_intrq;
 
/*
    STARTUP DEBUG LOGGING
        debugTimer <= debugTimer + 1;
*/
 
        if (bus_en)
            buffer_bus_second_cycle <= !buffer_bus_second_cycle;
        else
            buffer_bus_second_cycle <= 1'b0;
 
        if (bus_en & bus_wr & control_bus_addressed) begin
                if (bus_addr [3:2] == 2'b00) begin
                            operationFinished <= bus_din [4];
                        if (commandUnlocked)
                                    requestedWrite <= bus_din [2];
                            enableInterrupts <= bus_din [1];
                    end
                    else if (bus_addr [3:2] == 2'b01 & commandUnlocked) begin
                        requestedSectorCount <= bus_din [3:0];
                    end
                    else if (bus_addr [3:2] == 2'b10 & commandUnlocked) begin
                        requestedSectorAddress <= bus_din [27:0];
                    end
            end
 
        if (!io_wait) begin
/*
    STARTUP DEBUG LOGGING
            buffer_ata_write <= 1;
            if (buffer_ata_addr < 2000)
                buffer_ata_addr <= buffer_ata_addr + 2;
            buffer_ata_din <= io_data_in;
*/
            case (state)
 
                // startup sequence: ask for access to command regs
                    // and drive
                    5'd0: begin
                        io_en <= 1'b1;
                            io_write <= 1'b0;
                            io_addr <= `ADDR_ALTERNATE_STATUS;
                state <= 5'd1;
                    end
 
                // startup sequence: wait for command regs and
                    // drive, or select drive 0 if ready
                    5'd1: begin
                        if (io_data_in [7:6] == 2'b01) begin
                                    // ready, so select drive 0
                                    io_write <= 1'b1;
                                    io_addr <= `ADDR_LBA3_DRV;
                                    io_data_out <= 8'b11100000;
                                    state <= 5'd2;
                            end else begin
                                // busy, so keep asking
                            end
                end
 
                    // startup sequence: send "identify drive" command
                    5'd2: begin
                        io_write <= 1'b1;
                            io_addr <= `ADDR_COMMAND;
                            io_data_out <= 16'h00ec;
                            state <= 5'd3;
                    end
 
            // wait for the ATA to send an IRQ, then read the status register
                    5'd3: begin
                if (debounced_ata_intrq) begin
                    io_en <= 1'b1;
                    io_write <= 1'b0;
                    io_addr <= `ADDR_STATUS;
                            aux_counter <= 8'd60;
                    state <= 5'd4;
                end else begin
                    io_en <= 1'b0;
                    io_write <= 1'b0;
                end
                    end
 
 
                    // skip 60 words from the data buffer, then read
                    // the high 16 bits of the capacity
            5'd4: begin
                        io_write <= 1'b0;
                            io_addr <= `ADDR_DATA;
                            if (aux_counter == 0) state <= 5'd5;
                            else aux_counter <= aux_counter - 1;
            end
 
                // store the high 16 bits of the capacity just
                    // read and read the low 16 bits
                    5'd5: begin
                        io_write <= 1'b0;
                            io_addr <= `ADDR_DATA;
                            capacity [15:0] <= io_data_in;
                            state <= 5'd6;
                    end
 
                // store the low 16 bits of the capacity,
            // then read another 194 words to finish the
            // "identify drive" buffer
                    5'd6: begin
                            capacity [31:16] <= io_data_in;
                            state <= 5'd7;
                        io_write <= 1'b0;
                            io_addr <= `ADDR_DATA;
                aux_counter <= 8'd193; // one is read now
                    end
 
            // skip another 193 words from the buffer
                    5'd7: begin
                if (aux_counter == 0) begin
                    io_en <= 1'b0;
                    io_write <= 1'b0;
                    state <= 5'd8;
                    diskInitialized <= 1'b1;
                        end else begin
                    aux_counter <= aux_counter - 1;
                end
            end
 
    //----------------------------------------------------------
 
            // ready and waiting for commands. Only on this
            // state is write access from the on-chip bus
            // allowed. When a request arrives, write the
            // drive/head/lba3 register and goto state 9.
            5'd8: begin
                if (startBit) begin
                    state <= 5'd19;
                    io_en <= 1'b1;
                    io_write <= 1'b0;
                    io_addr <= `ADDR_STATUS;
                end else begin
                    io_en <= 1'b0;
                end
            end
 
            5'd19: begin
              if (io_data_in[7] == 0) begin
                    state <= 5'd9;
                    io_en <= 1'b1;
                    io_write <= 1'b1;
                    io_addr <= `ADDR_LBA3_DRV;
                    io_data_out <=
                        { 8'd0, 4'b1110, requestedSectorAddress [27:24] };
                    sector_counter <= 3'd0;
              end else begin
                // read status again
              end
            end
 
            // next, write the lba2 register
            5'd9: begin
                io_addr <= `ADDR_LBA2;
                io_data_out <= { 8'd0, requestedSectorAddress [23:16] };
                state <= 5'd10;
            end
 
            // next, write the lba1 register
            5'd10: begin
                io_addr <= `ADDR_LBA1;
                io_data_out <= { 8'd0, requestedSectorAddress [15:8] };
                state <= 5'd11;
            end
 
            // next, write the lba0 register
            5'd11: begin
                io_addr <= `ADDR_LBA0;
                io_data_out <= { 8'd0, requestedSectorAddress [7:0] };
                state <= 5'd12;
            end
 
            // next, write the sector count register
            5'd12: begin
                io_addr <= `ADDR_SECTOR_COUNT;
                io_data_out <= { 8'd0, 4'd0, requestedSectorCount };
                state <= 5'd13;
            end
 
            // finally, write the command register
            5'd13: begin
                io_addr <= `ADDR_COMMAND;
                io_data_out <= requestedWrite ? 16'h30 : 16'h20;
                state <= 5'd14;
            end
 
            // now branch whether reading or writing.
            // for reading, wait for IRQ, then read status
            // for writing, wait for DRQ and simultaneously
            // fetch the first word from the buffer
            5'd14: begin
                if (requestedWrite) begin
                    io_en <= 1'b1;
                    io_write <= 1'b0;
                    io_addr <= `ADDR_STATUS;
                    state <= 5'd17;
                    aux_counter <= 8'd0;
                end else begin
                    if (debounced_ata_intrq) begin
                        io_en <= 1'b1;
                        io_write <= 1'b0;
                        io_addr <= `ADDR_STATUS;
                        state <= 5'd15;
                    end else begin
                        io_en <= 1'b0;
                    end
                end
            end
 
            // read 256 words of data
            5'd15: begin
                io_en <= 1'b1;
                io_write <= 1'b0;
                io_addr <= `ADDR_DATA;
                aux_counter <= 8'd0;
                state <= 5'd16;
            end
 
            // sample data in, and read next if needed. Data sampling is
            // done directly by the blockRAM, and the necessary wiring is
            // defined above.
            5'd16: begin
                if (aux_counter == 8'd255) begin
                    if (requestedSectorCount == 4'b0001) begin
                        io_en <= 1'b0;
                        state <= 5'd8;
                        errorOutput <= 1'b0;
                        operationFinished <= 1'b1;
                    end else begin
                        if (debounced_ata_intrq) begin
                            requestedSectorCount <= requestedSectorCount - 1;
                            sector_counter <= sector_counter + 1;
                            io_en <= 1'b1;
                            io_write <= 1'b0;
                            io_addr <= `ADDR_STATUS;
                            state <= 5'd15;
                        end else begin
                            io_en <= 1'b0;
                            // last word of finished sector is sampled
                            // repeatedly here (harmless)
                        end
                    end
                end else begin
                    aux_counter <= aux_counter + 1;
                end
            end
 
            // if DRQ is not yet set, wait for it. Otherwise send the
            // first data word to the ATA and fetch the next one
            5'd17: begin
                if (io_data_in[7] == 0 && io_data_in[3] == 1) begin
                    io_en <= 1'b1;
                    io_write <= 1'b1;
                    io_addr <= `ADDR_DATA;
                    io_data_out <= buffer_ata_dout;
                    aux_counter <= aux_counter + 1;
                    state <= 5'd18;
                end else begin
                    // read status again
                end
            end
 
            // write words to the buffer until finished. Note that since
            // an ATA transfer cycle takes at least two clock cycles, the
            // buffer is always read to buffer_ata_dout before that register
            // is used. After the transfer is finished, wait for IRQ, then
            // read the status register and select the correct next state
            // depending on whether more sectors must follow.
            5'd18: begin
                // loop until done. All addressing is done automatically.
                if (aux_counter == 8'd0) begin
                    if (debounced_ata_intrq) begin
                        io_en <= 1'b1;
                        io_write <= 1'b0;
                        io_addr <= `ADDR_STATUS;
                        if (requestedSectorCount == 4'b0001) begin
                            state <= 5'd8;
                            errorOutput <= 1'b0;
                            operationFinished <= 1'b1;
                        end else begin
                            requestedSectorCount <= requestedSectorCount - 1;
                            sector_counter <= sector_counter + 1;
                            state <= 5'd17;
                        end
                    end else begin
                        io_en <= 1'b0;
                    end
                end else begin
                    io_data_out <= buffer_ata_dout;
                    aux_counter <= aux_counter + 1;
                end
            end
 
            endcase
        end else begin
/*
    STARTUP DEBUG LOGGING
            buffer_ata_write <= 0;
*/
        end
    end
end
 
endmodule

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[/] [eco32/] [trunk/] [fpga/] [mc/] [src/] [dsk/] [atactrl.v] - Blame information for rev 323

Line No.	Rev	Author	Line
1	121	hellwig	`//`
2			`// atactrl.v -- parallel ATA controller`
3			`//`
4	27	hellwig
5	121	hellwig
6	290	hellwig	`timescale 1ns/10ps
7			`default_nettype none
8
9
10	121	hellwig	`define ADDR_ALTERNATE_STATUS 4'b0110
11			`define ADDR_DEVICE_CONTROL 4'b0110
12			`define ADDR_DEVICE_ADDRESS 4'b0111
13			`define ADDR_DATA 4'b1000
14			`define ADDR_ERROR 4'b1001
15			`define ADDR_FEATURES 4'b1001
16			`define ADDR_SECTOR_COUNT 4'b1010
17			`define ADDR_LBA0 4'b1011
18			`define ADDR_LBA1 4'b1100
19			`define ADDR_LBA2 4'b1101
20			`define ADDR_LBA3_DRV 4'b1110
21			`define ADDR_STATUS 4'b1111
22			`define ADDR_COMMAND 4'b1111
23
24
25	27	hellwig	`module ata_ctrl (`
26			`input clk, reset,`
27
28			`input bus_en, bus_wr,`
29			`input [19:2] bus_addr,`
30			`input [31:0] bus_din,`
31			`output [31:0] bus_dout,`
32			`output bus_wait,`
33			`output bus_irq,`
34
35			`inout [15:0] ata_d,`
36			`output [2:0] ata_a,`
37			`output ata_cs0_n, ata_cs1_n,`
38			`output ata_dior_n, ata_diow_n,`
39			`input ata_intrq,`
40			`input ata_dmarq,`
41			`output ata_dmack_n,`
42			`input ata_iordy`
43			`);`
44
45			`// --- ATA IRQ line debouncing`
46			`reg debounced_ata_intrq, prev_ata_intrq;`
47			`reg [3:0] ata_intrq_debounce_counter;`
48
49			`// --- disk buffer`
50
51			`// interface to the bus`
52			`wire buffer_bus_wait;`
53			`wire [31:0] buffer_bus_dout;`
54
55			`// interface to the state machine`
56			`wire buffer_ata_write;`
57			`wire [11:1] buffer_ata_addr;`
58			`wire [15:0] buffer_ata_din;`
59			`wire [15:0] buffer_ata_dout;`
60			`wire buffer_bus_addressed;`
61			`wire buffer_bus_write;`
62			`reg buffer_bus_second_cycle;`
63
64	290	hellwig	`ata_buffer ata_buffer_1(`
65	27	hellwig	`.clk (clk),`
66			`.bus_write (buffer_bus_write),`
67			`.bus_addr (bus_addr [11:2]),`
68			`.bus_din (bus_din),`
69			`.bus_dout (buffer_bus_dout),`
70			`.ata_write (buffer_ata_write),`
71			`.ata_addr (buffer_ata_addr),`
72			`.ata_din (buffer_ata_din),`
73			`.ata_dout (buffer_ata_dout)`
74			`);`
75
76			`assign buffer_bus_addressed = bus_addr [19];`
77			`assign buffer_bus_wait = bus_en & !buffer_bus_second_cycle;`
78			`assign buffer_bus_write = bus_en & bus_wr &`
79			`buffer_bus_addressed & !buffer_bus_second_cycle;`
80
81			`// --- control registers`
82
83			`// interface to the bus`
84			`wire control_bus_wait;`
85			`wire [31:0] control_bus_dout;`
86
87			`// interface to the state machine`
88			`reg [31:0] capacity;`
89			`reg [27:0] requestedSectorAddress;`
90			`reg [3:0] requestedSectorCount;`
91			`wire commandUnlocked;`
92			`reg enableInterrupts, requestedWrite, errorOutput;`
93			`reg operationFinished, diskInitialized;`
94			`wire control_bus_addressed;`
95
96			`assign control_bus_addressed = !bus_addr[19];`
97			`assign control_bus_wait = 0;`
98			`assign control_bus_dout =`
99			`(bus_addr [3:2] == 2'b00) ? {ata_dmarq, 25'd0,`
100			`diskInitialized, operationFinished,`
101			`errorOutput, requestedWrite,`
102			`enableInterrupts, 1'b0} :`
103			`(bus_addr [3:2] == 2'b01) ? { 28'd0, requestedSectorCount } :`
104			`(bus_addr [3:2] == 2'b10) ? { 4'd0, requestedSectorAddress } :`
105			`capacity;`
106
107			`// --- ATA IO component`
108
109			`reg io_en, io_write;`
110			`wire io_wait;`
111			`reg [3:0] io_addr;`
112			`reg [15:0] io_data_out;`
113			`wire [15:0] io_data_in;`
114
115			`assign ata_dmack_n = 1'b1;`
116			`ata_io io (`
117			`.clk(clk),`
118			`.reset(reset),`
119			`.bus_en(io_en),`
120			`.bus_wr(io_write),`
121			`.bus_addr(io_addr),`
122			`.bus_din(io_data_out),`
123			`.bus_dout(io_data_in),`
124			`.bus_wait(io_wait),`
125			`.ata_d(ata_d),`
126			`.ata_a(ata_a),`
127			`.ata_cs0_n(ata_cs0_n),`
128			`.ata_cs1_n(ata_cs1_n),`
129			`.ata_dior_n(ata_dior_n),`
130			`.ata_diow_n(ata_diow_n),`
131			`.ata_iordy(ata_iordy)`
132			`);`
133
134			`// --- bus interface`
135
136			`assign bus_dout = bus_addr [19] ? buffer_bus_dout : control_bus_dout;`
137			`assign bus_wait = bus_addr [19] ? buffer_bus_wait : control_bus_wait;`
138			`assign bus_irq = enableInterrupts & operationFinished;`
139
140			`// --- state machine`
141
142			`reg [4:0] state;`
143			`reg [7:0] aux_counter;`
144			`reg [2:0] sector_counter;`
145			`/*`
146			`STARTUP DEBUG LOGGING`
147			`reg [15:0] debugTimer;`
148			`*/`
149
150			`wire startBit;`
151			`assign commandUnlocked = (state == 5'd8);`
152			`assign startBit = bus_en & bus_wr &`
153			`(!bus_addr [19]) & (bus_addr [3:2] == 2'b00) &`
154			`bus_din [0];`
155
156			`assign buffer_ata_write = (state == 5'd16) & (!io_wait);`
157			`assign buffer_ata_addr = {sector_counter, aux_counter [7:0]};`
158			`assign buffer_ata_din = io_data_in;`
159
160			`always @(posedge clk) begin`
161			`if (reset) begin`
162
163			`prev_ata_intrq <= 1'b0;`
164			`debounced_ata_intrq <= 1'b0;`
165			`ata_intrq_debounce_counter <= 4'b0;`
166
167			`buffer_bus_second_cycle <= 1'b0;`
168
169			`capacity <= 32'd0;`
170			`requestedSectorAddress <= 32'd0;`
171			`requestedSectorCount <= 4'b0000;`
172
173			`enableInterrupts <= 1'b0;`
174			`requestedWrite <= 1'b0;`
175			`errorOutput <= 1'b0;`
176			`operationFinished <= 1'b0;`
177			`diskInitialized <= 1'b0;`
178
179			`io_en <= 1'b0;`
180			`io_write <= 1'b0;`
181			`io_addr <= 32'd0;`
182			`io_data_out <= 16'd0;`
183
184			`state <= 5'd0;`
185			`aux_counter <= 8'd0;`
186			`sector_counter <= 3'd0;`
187
188			`/*`
189			`STARTUP DEBUG LOGGING`
190			`debugTimer <= 16'd0;`
191			`*/`
192
193			`end else begin`
194
195			`if (ata_intrq == prev_ata_intrq) begin`
196			`if (ata_intrq_debounce_counter == 4'd0) begin`
197			`debounced_ata_intrq <= ata_intrq;`
198			`end else begin`
199			`ata_intrq_debounce_counter <= ata_intrq_debounce_counter - 1;`
200			`end`
201			`end else begin`
202			`ata_intrq_debounce_counter <= 4'd10;`
203			`end`
204			`prev_ata_intrq <= ata_intrq;`
205
206			`/*`
207			`STARTUP DEBUG LOGGING`
208			`debugTimer <= debugTimer + 1;`
209			`*/`
210
211			`if (bus_en)`
212			`buffer_bus_second_cycle <= !buffer_bus_second_cycle;`
213			`else`
214			`buffer_bus_second_cycle <= 1'b0;`
215
216			`if (bus_en & bus_wr & control_bus_addressed) begin`
217			`if (bus_addr [3:2] == 2'b00) begin`
218			`operationFinished <= bus_din [4];`
219			`if (commandUnlocked)`
220			`requestedWrite <= bus_din [2];`
221			`enableInterrupts <= bus_din [1];`
222			`end`
223			`else if (bus_addr [3:2] == 2'b01 & commandUnlocked) begin`
224			`requestedSectorCount <= bus_din [3:0];`
225			`end`
226			`else if (bus_addr [3:2] == 2'b10 & commandUnlocked) begin`
227			`requestedSectorAddress <= bus_din [27:0];`
228			`end`
229			`end`
230
231			`if (!io_wait) begin`
232			`/*`
233			`STARTUP DEBUG LOGGING`
234			`buffer_ata_write <= 1;`
235			`if (buffer_ata_addr < 2000)`
236			`buffer_ata_addr <= buffer_ata_addr + 2;`
237			`buffer_ata_din <= io_data_in;`
238			`*/`
239			`case (state)`
240
241			`// startup sequence: ask for access to command regs`
242			`// and drive`
243			`5'd0: begin`
244			`io_en <= 1'b1;`
245			`io_write <= 1'b0;`
246			io_addr <= `ADDR_ALTERNATE_STATUS;
247			`state <= 5'd1;`
248			`end`
249
250			`// startup sequence: wait for command regs and`
251			`// drive, or select drive 0 if ready`
252			`5'd1: begin`
253			`if (io_data_in [7:6] == 2'b01) begin`
254			`// ready, so select drive 0`
255			`io_write <= 1'b1;`
256			io_addr <= `ADDR_LBA3_DRV;
257			`io_data_out <= 8'b11100000;`
258			`state <= 5'd2;`
259			`end else begin`
260			`// busy, so keep asking`
261			`end`
262			`end`
263
264			`// startup sequence: send "identify drive" command`
265			`5'd2: begin`
266			`io_write <= 1'b1;`
267			io_addr <= `ADDR_COMMAND;
268			`io_data_out <= 16'h00ec;`
269			`state <= 5'd3;`
270			`end`
271
272			`// wait for the ATA to send an IRQ, then read the status register`
273			`5'd3: begin`
274			`if (debounced_ata_intrq) begin`
275			`io_en <= 1'b1;`
276			`io_write <= 1'b0;`
277			io_addr <= `ADDR_STATUS;
278			`aux_counter <= 8'd60;`
279			`state <= 5'd4;`
280			`end else begin`
281			`io_en <= 1'b0;`
282			`io_write <= 1'b0;`
283			`end`
284			`end`
285
286
287			`// skip 60 words from the data buffer, then read`
288			`// the high 16 bits of the capacity`
289			`5'd4: begin`
290			`io_write <= 1'b0;`
291			io_addr <= `ADDR_DATA;
292			`if (aux_counter == 0) state <= 5'd5;`
293			`else aux_counter <= aux_counter - 1;`
294			`end`
295
296			`// store the high 16 bits of the capacity just`
297			`// read and read the low 16 bits`
298			`5'd5: begin`
299			`io_write <= 1'b0;`
300			io_addr <= `ADDR_DATA;
301			`capacity [15:0] <= io_data_in;`
302			`state <= 5'd6;`
303			`end`
304
305			`// store the low 16 bits of the capacity,`
306			`// then read another 194 words to finish the`
307			`// "identify drive" buffer`
308			`5'd6: begin`
309			`capacity [31:16] <= io_data_in;`
310			`state <= 5'd7;`
311			`io_write <= 1'b0;`
312			io_addr <= `ADDR_DATA;
313			`aux_counter <= 8'd193; // one is read now`
314			`end`
315
316			`// skip another 193 words from the buffer`
317			`5'd7: begin`
318			`if (aux_counter == 0) begin`
319			`io_en <= 1'b0;`
320			`io_write <= 1'b0;`
321			`state <= 5'd8;`
322			`diskInitialized <= 1'b1;`
323			`end else begin`
324			`aux_counter <= aux_counter - 1;`
325			`end`
326			`end`
327
328			`//----------------------------------------------------------`
329
330			`// ready and waiting for commands. Only on this`
331			`// state is write access from the on-chip bus`
332			`// allowed. When a request arrives, write the`
333			`// drive/head/lba3 register and goto state 9.`
334			`5'd8: begin`
335			`if (startBit) begin`
336			`state <= 5'd19;`
337			`io_en <= 1'b1;`
338			`io_write <= 1'b0;`
339			io_addr <= `ADDR_STATUS;
340			`end else begin`
341			`io_en <= 1'b0;`
342			`end`
343			`end`
344
345			`5'd19: begin`
346			`if (io_data_in[7] == 0) begin`
347			`state <= 5'd9;`
348			`io_en <= 1'b1;`
349			`io_write <= 1'b1;`
350			io_addr <= `ADDR_LBA3_DRV;
351			`io_data_out <=`
352			`{ 8'd0, 4'b1110, requestedSectorAddress [27:24] };`
353			`sector_counter <= 3'd0;`
354			`end else begin`
355			`// read status again`
356			`end`
357			`end`
358
359			`// next, write the lba2 register`
360			`5'd9: begin`
361			io_addr <= `ADDR_LBA2;
362			`io_data_out <= { 8'd0, requestedSectorAddress [23:16] };`
363			`state <= 5'd10;`
364			`end`
365
366			`// next, write the lba1 register`
367			`5'd10: begin`
368			io_addr <= `ADDR_LBA1;
369			`io_data_out <= { 8'd0, requestedSectorAddress [15:8] };`
370			`state <= 5'd11;`
371			`end`
372
373			`// next, write the lba0 register`
374			`5'd11: begin`
375			io_addr <= `ADDR_LBA0;
376			`io_data_out <= { 8'd0, requestedSectorAddress [7:0] };`
377			`state <= 5'd12;`
378			`end`
379
380			`// next, write the sector count register`
381			`5'd12: begin`
382			io_addr <= `ADDR_SECTOR_COUNT;
383			`io_data_out <= { 8'd0, 4'd0, requestedSectorCount };`
384			`state <= 5'd13;`
385			`end`
386
387			`// finally, write the command register`
388			`5'd13: begin`
389			io_addr <= `ADDR_COMMAND;
390			`io_data_out <= requestedWrite ? 16'h30 : 16'h20;`
391			`state <= 5'd14;`
392			`end`
393
394			`// now branch whether reading or writing.`
395			`// for reading, wait for IRQ, then read status`
396			`// for writing, wait for DRQ and simultaneously`
397			`// fetch the first word from the buffer`
398			`5'd14: begin`
399			`if (requestedWrite) begin`
400			`io_en <= 1'b1;`
401			`io_write <= 1'b0;`
402			io_addr <= `ADDR_STATUS;
403			`state <= 5'd17;`
404			`aux_counter <= 8'd0;`
405			`end else begin`
406			`if (debounced_ata_intrq) begin`
407			`io_en <= 1'b1;`
408			`io_write <= 1'b0;`
409			io_addr <= `ADDR_STATUS;
410			`state <= 5'd15;`
411			`end else begin`
412			`io_en <= 1'b0;`
413			`end`
414			`end`
415			`end`
416
417			`// read 256 words of data`
418			`5'd15: begin`
419			`io_en <= 1'b1;`
420			`io_write <= 1'b0;`
421			io_addr <= `ADDR_DATA;
422			`aux_counter <= 8'd0;`
423			`state <= 5'd16;`
424			`end`
425
426			`// sample data in, and read next if needed. Data sampling is`
427			`// done directly by the blockRAM, and the necessary wiring is`
428			`// defined above.`
429			`5'd16: begin`
430			`if (aux_counter == 8'd255) begin`
431			`if (requestedSectorCount == 4'b0001) begin`
432			`io_en <= 1'b0;`
433			`state <= 5'd8;`
434			`errorOutput <= 1'b0;`
435			`operationFinished <= 1'b1;`
436			`end else begin`
437			`if (debounced_ata_intrq) begin`
438			`requestedSectorCount <= requestedSectorCount - 1;`
439			`sector_counter <= sector_counter + 1;`
440			`io_en <= 1'b1;`
441			`io_write <= 1'b0;`
442			io_addr <= `ADDR_STATUS;
443			`state <= 5'd15;`
444			`end else begin`
445			`io_en <= 1'b0;`
446			`// last word of finished sector is sampled`
447			`// repeatedly here (harmless)`
448			`end`
449			`end`
450			`end else begin`
451			`aux_counter <= aux_counter + 1;`
452			`end`
453			`end`
454
455			`// if DRQ is not yet set, wait for it. Otherwise send the`
456			`// first data word to the ATA and fetch the next one`
457			`5'd17: begin`
458			`if (io_data_in[7] == 0 && io_data_in[3] == 1) begin`
459			`io_en <= 1'b1;`
460			`io_write <= 1'b1;`
461			io_addr <= `ADDR_DATA;
462			`io_data_out <= buffer_ata_dout;`
463			`aux_counter <= aux_counter + 1;`
464			`state <= 5'd18;`
465			`end else begin`
466			`// read status again`
467			`end`
468			`end`
469
470			`// write words to the buffer until finished. Note that since`
471			`// an ATA transfer cycle takes at least two clock cycles, the`
472			`// buffer is always read to buffer_ata_dout before that register`
473			`// is used. After the transfer is finished, wait for IRQ, then`
474			`// read the status register and select the correct next state`
475			`// depending on whether more sectors must follow.`
476			`5'd18: begin`
477			`// loop until done. All addressing is done automatically.`
478			`if (aux_counter == 8'd0) begin`
479			`if (debounced_ata_intrq) begin`
480			`io_en <= 1'b1;`
481			`io_write <= 1'b0;`
482			io_addr <= `ADDR_STATUS;
483			`if (requestedSectorCount == 4'b0001) begin`
484			`state <= 5'd8;`
485			`errorOutput <= 1'b0;`
486			`operationFinished <= 1'b1;`
487			`end else begin`
488			`requestedSectorCount <= requestedSectorCount - 1;`
489			`sector_counter <= sector_counter + 1;`
490			`state <= 5'd17;`
491			`end`
492			`end else begin`
493			`io_en <= 1'b0;`
494			`end`
495			`end else begin`
496			`io_data_out <= buffer_ata_dout;`
497			`aux_counter <= aux_counter + 1;`
498			`end`
499			`end`
500
501			`endcase`
502			`end else begin`
503			`/*`
504			`STARTUP DEBUG LOGGING`
505			`buffer_ata_write <= 0;`
506			`*/`
507			`end`
508			`end`
509			`end`
510
511			`endmodule`