module axi_cdma #
(
    // Width of data bus in bits
    parameter AXI_DATA_WIDTH = 32,
    // Width of address bus in bits
    parameter AXI_ADDR_WIDTH = 16,
    // Width of wstrb (width of data bus in words)
    parameter AXI_STRB_WIDTH = (AXI_DATA_WIDTH/8),
    // Width of AXI ID signal
    parameter AXI_ID_WIDTH = 8,
    // Maximum AXI burst length to generate
    parameter AXI_MAX_BURST_LEN = 16,
    // Width of length field
    parameter LEN_WIDTH = 20,
    // Width of tag field
    parameter TAG_WIDTH = 8,
    // Enable support for unaligned transfers
    parameter ENABLE_UNALIGNED = 0
)
(
    input  wire                       clk,
    input  wire                       rst,

    /*
     * AXI descriptor input
     */
    input  wire [AXI_ADDR_WIDTH-1:0]  s_axis_desc_read_addr,
    input  wire [AXI_ADDR_WIDTH-1:0]  s_axis_desc_write_addr,
    input  wire [LEN_WIDTH-1:0]       s_axis_desc_len,
    input  wire [TAG_WIDTH-1:0]       s_axis_desc_tag,
    input  wire                       s_axis_desc_valid,
    output wire                       s_axis_desc_ready,

    /*
     * AXI descriptor status output
     */
    output wire [TAG_WIDTH-1:0]       m_axis_desc_status_tag,
    output wire                       m_axis_desc_status_valid,

    /*
     * AXI write master interface
     */
    output wire [AXI_ID_WIDTH-1:0]    m_axi_awid,
    output wire [AXI_ADDR_WIDTH-1:0]  m_axi_awaddr,
    output wire [7:0]                 m_axi_awlen,
    output wire [2:0]                 m_axi_awsize,
    output wire [1:0]                 m_axi_awburst,
    output wire                       m_axi_awlock,
    output wire [3:0]                 m_axi_awcache,
    output wire [2:0]                 m_axi_awprot,
    output wire                       m_axi_awvalid,
    input  wire                       m_axi_awready,
    output wire [AXI_DATA_WIDTH-1:0]  m_axi_wdata,
    output wire [AXI_STRB_WIDTH-1:0]  m_axi_wstrb,
    output wire                       m_axi_wlast,
    output wire                       m_axi_wvalid,
    input  wire                       m_axi_wready,
    input  wire [AXI_ID_WIDTH-1:0]    m_axi_bid,
    input  wire [1:0]                 m_axi_bresp,
    input  wire                       m_axi_bvalid,
    output wire                       m_axi_bready,

    /*
     * AXI read master interface
     */
    output wire [AXI_ID_WIDTH-1:0]    m_axi_arid,
    output wire [AXI_ADDR_WIDTH-1:0]  m_axi_araddr,
    output wire [7:0]                 m_axi_arlen,
    output wire [2:0]                 m_axi_arsize,
    output wire [1:0]                 m_axi_arburst,
    output wire                       m_axi_arlock,
    output wire [3:0]                 m_axi_arcache,
    output wire [2:0]                 m_axi_arprot,
    output wire                       m_axi_arvalid,
    input  wire                       m_axi_arready,
    input  wire [AXI_ID_WIDTH-1:0]    m_axi_rid,
    input  wire [AXI_DATA_WIDTH-1:0]  m_axi_rdata,
    input  wire [1:0]                 m_axi_rresp,
    input  wire                       m_axi_rlast,
    input  wire                       m_axi_rvalid,
    output wire                       m_axi_rready,

    /*
     * Configuration
     */
    input  wire                       enable
);

parameter AXI_WORD_WIDTH = AXI_STRB_WIDTH;
parameter AXI_WORD_SIZE = AXI_DATA_WIDTH/AXI_WORD_WIDTH;
parameter AXI_BURST_SIZE = $clog2(AXI_STRB_WIDTH);
parameter AXI_MAX_BURST_SIZE = AXI_MAX_BURST_LEN << AXI_BURST_SIZE;

parameter OFFSET_WIDTH = AXI_STRB_WIDTH > 1 ? $clog2(AXI_STRB_WIDTH) : 1;
parameter OFFSET_MASK = AXI_STRB_WIDTH > 1 ? {OFFSET_WIDTH{1'b1}} : 0;
parameter ADDR_MASK = {AXI_ADDR_WIDTH{1'b1}} << $clog2(AXI_STRB_WIDTH);
parameter CYCLE_COUNT_WIDTH = LEN_WIDTH - AXI_BURST_SIZE + 1;

parameter STATUS_FIFO_ADDR_WIDTH = 5;

// bus width assertions
initial begin
    if (AXI_WORD_SIZE * AXI_STRB_WIDTH != AXI_DATA_WIDTH) begin
        $error("Error: AXI data width not evenly divisble (instance %m)");
        $finish;
    end

    if (2**$clog2(AXI_WORD_WIDTH) != AXI_WORD_WIDTH) begin
        $error("Error: AXI word width must be even power of two (instance %m)");
        $finish;
    end

    if (AXI_MAX_BURST_LEN < 1 || AXI_MAX_BURST_LEN > 256) begin
        $error("Error: AXI_MAX_BURST_LEN must be between 1 and 256 (instance %m)");
        $finish;
    end
end

localparam [1:0]
    READ_STATE_IDLE = 2'd0,
    READ_STATE_START = 2'd1,
    READ_STATE_REQ = 2'd2;

reg [1:0] read_state_reg = READ_STATE_IDLE, read_state_next;

localparam [0:0]
    AXI_STATE_IDLE = 1'd0,
    AXI_STATE_WRITE = 1'd1;

reg [0:0] axi_state_reg = AXI_STATE_IDLE, axi_state_next;

// datapath control signals
reg transfer_in_save;
reg axi_cmd_ready;
reg status_fifo_we;

reg [AXI_ADDR_WIDTH-1:0] read_addr_reg = {AXI_ADDR_WIDTH{1'b0}}, read_addr_next;
reg [AXI_ADDR_WIDTH-1:0] write_addr_reg = {AXI_ADDR_WIDTH{1'b0}}, write_addr_next;
reg [LEN_WIDTH-1:0] op_word_count_reg = {LEN_WIDTH{1'b0}}, op_word_count_next;
reg [LEN_WIDTH-1:0] tr_word_count_reg = {LEN_WIDTH{1'b0}}, tr_word_count_next;
reg [LEN_WIDTH-1:0] axi_word_count_reg = {LEN_WIDTH{1'b0}}, axi_word_count_next;

reg [AXI_ADDR_WIDTH-1:0] axi_cmd_addr_reg = {AXI_ADDR_WIDTH{1'b0}}, axi_cmd_addr_next;
reg [OFFSET_WIDTH-1:0] axi_cmd_offset_reg = {OFFSET_WIDTH{1'b0}}, axi_cmd_offset_next;
reg [OFFSET_WIDTH-1:0] axi_cmd_first_cycle_offset_reg = {OFFSET_WIDTH{1'b0}}, axi_cmd_first_cycle_offset_next;
reg [OFFSET_WIDTH-1:0] axi_cmd_last_cycle_offset_reg = {OFFSET_WIDTH{1'b0}}, axi_cmd_last_cycle_offset_next;
reg [CYCLE_COUNT_WIDTH-1:0] axi_cmd_input_cycle_count_reg = {CYCLE_COUNT_WIDTH{1'b0}}, axi_cmd_input_cycle_count_next;
reg [CYCLE_COUNT_WIDTH-1:0] axi_cmd_output_cycle_count_reg = {CYCLE_COUNT_WIDTH{1'b0}}, axi_cmd_output_cycle_count_next;
reg axi_cmd_bubble_cycle_reg = 1'b0, axi_cmd_bubble_cycle_next;
reg axi_cmd_last_transfer_reg = 1'b0, axi_cmd_last_transfer_next;
reg [TAG_WIDTH-1:0] axi_cmd_tag_reg = {TAG_WIDTH{1'b0}}, axi_cmd_tag_next;
reg axi_cmd_valid_reg = 1'b0, axi_cmd_valid_next;

reg [OFFSET_WIDTH-1:0] offset_reg = {OFFSET_WIDTH{1'b0}}, offset_next;
reg [OFFSET_WIDTH-1:0] first_cycle_offset_reg = {OFFSET_WIDTH{1'b0}}, first_cycle_offset_next;
reg [OFFSET_WIDTH-1:0] last_cycle_offset_reg = {OFFSET_WIDTH{1'b0}}, last_cycle_offset_next;
reg [CYCLE_COUNT_WIDTH-1:0] input_cycle_count_reg = {CYCLE_COUNT_WIDTH{1'b0}}, input_cycle_count_next;
reg [CYCLE_COUNT_WIDTH-1:0] output_cycle_count_reg = {CYCLE_COUNT_WIDTH{1'b0}}, output_cycle_count_next;
reg input_active_reg = 1'b0, input_active_next;
reg output_active_reg = 1'b0, output_active_next;
reg bubble_cycle_reg = 1'b0, bubble_cycle_next;
reg first_input_cycle_reg = 1'b0, first_input_cycle_next;
reg first_output_cycle_reg = 1'b0, first_output_cycle_next;
reg output_last_cycle_reg = 1'b0, output_last_cycle_next;
reg last_transfer_reg = 1'b0, last_transfer_next;

reg [TAG_WIDTH-1:0] tag_reg = {TAG_WIDTH{1'b0}}, tag_next;

reg [STATUS_FIFO_ADDR_WIDTH+1-1:0] status_fifo_wr_ptr_reg = 0, status_fifo_wr_ptr_next;
reg [STATUS_FIFO_ADDR_WIDTH+1-1:0] status_fifo_rd_ptr_reg = 0, status_fifo_rd_ptr_next;
reg [TAG_WIDTH-1:0] status_fifo_tag[(2**STATUS_FIFO_ADDR_WIDTH)-1:0];
reg status_fifo_last[(2**STATUS_FIFO_ADDR_WIDTH)-1:0];
reg [TAG_WIDTH-1:0] status_fifo_wr_tag;
reg status_fifo_wr_last;

reg s_axis_desc_ready_reg = 1'b0, s_axis_desc_ready_next;

reg [TAG_WIDTH-1:0] m_axis_desc_status_tag_reg = {TAG_WIDTH{1'b0}}, m_axis_desc_status_tag_next;
reg m_axis_desc_status_valid_reg = 1'b0, m_axis_desc_status_valid_next;

reg [AXI_ADDR_WIDTH-1:0] m_axi_araddr_reg = {AXI_ADDR_WIDTH{1'b0}}, m_axi_araddr_next;
reg [7:0] m_axi_arlen_reg = 8'd0, m_axi_arlen_next;
reg m_axi_arvalid_reg = 1'b0, m_axi_arvalid_next;
reg m_axi_rready_reg = 1'b0, m_axi_rready_next;

reg [AXI_ADDR_WIDTH-1:0] m_axi_awaddr_reg = {AXI_ADDR_WIDTH{1'b0}}, m_axi_awaddr_next;
reg [7:0] m_axi_awlen_reg = 8'd0, m_axi_awlen_next;
reg m_axi_awvalid_reg = 1'b0, m_axi_awvalid_next;
reg m_axi_bready_reg = 1'b0, m_axi_bready_next;

reg [AXI_DATA_WIDTH-1:0] save_axi_rdata_reg = {AXI_DATA_WIDTH{1'b0}};

wire [AXI_DATA_WIDTH-1:0] shift_axi_rdata = {m_axi_rdata, save_axi_rdata_reg} >> ((AXI_STRB_WIDTH-offset_reg)*AXI_WORD_SIZE);

// internal datapath
reg  [AXI_DATA_WIDTH-1:0] m_axi_wdata_int;
reg  [AXI_STRB_WIDTH-1:0] m_axi_wstrb_int;
reg                       m_axi_wlast_int;
reg                       m_axi_wvalid_int;
reg                       m_axi_wready_int_reg = 1'b0;
wire                      m_axi_wready_int_early;

assign s_axis_desc_ready = s_axis_desc_ready_reg;

assign m_axis_desc_status_tag = m_axis_desc_status_tag_reg;
assign m_axis_desc_status_valid = m_axis_desc_status_valid_reg;

assign m_axi_arid = {AXI_ID_WIDTH{1'b0}};
assign m_axi_araddr = m_axi_araddr_reg;
assign m_axi_arlen = m_axi_arlen_reg;
assign m_axi_arsize = AXI_BURST_SIZE;
assign m_axi_arburst = 2'b01;
assign m_axi_arlock = 1'b0;
assign m_axi_arcache = 4'b0011;
assign m_axi_arprot = 3'b010;
assign m_axi_arvalid = m_axi_arvalid_reg;
assign m_axi_rready = m_axi_rready_reg;

assign m_axi_awid = {AXI_ID_WIDTH{1'b0}};
assign m_axi_awaddr = m_axi_awaddr_reg;
assign m_axi_awlen = m_axi_awlen_reg;
assign m_axi_awsize = AXI_BURST_SIZE;
assign m_axi_awburst = 2'b01;
assign m_axi_awlock = 1'b0;
assign m_axi_awcache = 4'b0011;
assign m_axi_awprot = 3'b010;
assign m_axi_awvalid = m_axi_awvalid_reg;
assign m_axi_bready = m_axi_bready_reg;

wire [AXI_ADDR_WIDTH-1:0] read_addr_plus_max_burst = read_addr_reg + AXI_MAX_BURST_SIZE;
wire [AXI_ADDR_WIDTH-1:0] read_addr_plus_op_count = read_addr_reg + op_word_count_reg;
wire [AXI_ADDR_WIDTH-1:0] read_addr_plus_axi_count = read_addr_reg + axi_word_count_reg;

wire [AXI_ADDR_WIDTH-1:0] write_addr_plus_max_burst = write_addr_reg + AXI_MAX_BURST_SIZE;
wire [AXI_ADDR_WIDTH-1:0] write_addr_plus_op_count = write_addr_reg + op_word_count_reg;
wire [AXI_ADDR_WIDTH-1:0] write_addr_plus_axi_count = write_addr_reg + axi_word_count_reg;

always @* begin
    read_state_next = READ_STATE_IDLE;

    s_axis_desc_ready_next = 1'b0;

    m_axi_araddr_next = m_axi_araddr_reg;
    m_axi_arlen_next = m_axi_arlen_reg;
    m_axi_arvalid_next = m_axi_arvalid_reg && !m_axi_arready;

    read_addr_next = read_addr_reg;
    write_addr_next = write_addr_reg;
    op_word_count_next = op_word_count_reg;
    tr_word_count_next = tr_word_count_reg;
    axi_word_count_next = axi_word_count_reg;

    axi_cmd_addr_next = axi_cmd_addr_reg;
    axi_cmd_offset_next = axi_cmd_offset_reg;
    axi_cmd_first_cycle_offset_next = axi_cmd_first_cycle_offset_reg;
    axi_cmd_last_cycle_offset_next = axi_cmd_last_cycle_offset_reg;
    axi_cmd_input_cycle_count_next = axi_cmd_input_cycle_count_reg;
    axi_cmd_output_cycle_count_next = axi_cmd_output_cycle_count_reg;
    axi_cmd_bubble_cycle_next = axi_cmd_bubble_cycle_reg;
    axi_cmd_last_transfer_next = axi_cmd_last_transfer_reg;
    axi_cmd_tag_next = axi_cmd_tag_reg;
    axi_cmd_valid_next = axi_cmd_valid_reg && !axi_cmd_ready;

    case (read_state_reg)
        READ_STATE_IDLE: begin
            // idle state - load new descriptor to start operation
            s_axis_desc_ready_next = !axi_cmd_valid_reg && enable;

            if (s_axis_desc_ready && s_axis_desc_valid) begin
                if (ENABLE_UNALIGNED) begin
                    read_addr_next = s_axis_desc_read_addr;
                    write_addr_next = s_axis_desc_write_addr;
                end else begin
                    read_addr_next = s_axis_desc_read_addr & ADDR_MASK;
                    write_addr_next = s_axis_desc_write_addr & ADDR_MASK;
                end
                axi_cmd_tag_next = s_axis_desc_tag;
                op_word_count_next = s_axis_desc_len;

                s_axis_desc_ready_next = 1'b0;
                read_state_next = READ_STATE_START;
            end else begin
                read_state_next = READ_STATE_IDLE;
            end
        end
        READ_STATE_START: begin
            // start state - compute write length
            if (!axi_cmd_valid_reg) begin
                if (op_word_count_reg <= AXI_MAX_BURST_SIZE - (write_addr_reg & OFFSET_MASK)) begin
                    // packet smaller than max burst size
                    if (write_addr_reg[12] != write_addr_plus_op_count[12]) begin
                        // crosses 4k boundary
                        axi_word_count_next = 13'h1000 - write_addr_reg[11:0];
                    end else begin
                        // does not cross 4k boundary
                        axi_word_count_next = op_word_count_reg;
                    end
                end else begin
                    // packet larger than max burst size
                    if (write_addr_reg[12] != write_addr_plus_max_burst[12]) begin
                        // crosses 4k boundary
                        axi_word_count_next = 13'h1000 - write_addr_reg[11:0];
                    end else begin
                        // does not cross 4k boundary
                        axi_word_count_next = AXI_MAX_BURST_SIZE - (write_addr_reg & OFFSET_MASK);
                    end
                end

                write_addr_next = write_addr_reg + axi_word_count_next;
                op_word_count_next = op_word_count_reg - axi_word_count_next;

                axi_cmd_addr_next = write_addr_reg;
                if (ENABLE_UNALIGNED) begin
                    axi_cmd_input_cycle_count_next = (axi_word_count_next + (read_addr_reg & OFFSET_MASK) - 1) >> AXI_BURST_SIZE;
                    axi_cmd_output_cycle_count_next = (axi_word_count_next + (write_addr_reg & OFFSET_MASK) - 1) >> AXI_BURST_SIZE;
                    axi_cmd_offset_next = (write_addr_reg & OFFSET_MASK) - (read_addr_reg & OFFSET_MASK);
                    axi_cmd_bubble_cycle_next = (read_addr_reg & OFFSET_MASK) > (write_addr_reg & OFFSET_MASK);
                    axi_cmd_first_cycle_offset_next = write_addr_reg & OFFSET_MASK;
                    axi_cmd_last_cycle_offset_next = axi_cmd_first_cycle_offset_next + axi_word_count_next & OFFSET_MASK;
                end else begin
                    axi_cmd_input_cycle_count_next = (axi_word_count_next - 1) >> AXI_BURST_SIZE;
                    axi_cmd_output_cycle_count_next = (axi_word_count_next - 1) >> AXI_BURST_SIZE;
                    axi_cmd_offset_next = 0;
                    axi_cmd_bubble_cycle_next = 0;
                    axi_cmd_first_cycle_offset_next = 0;
                    axi_cmd_last_cycle_offset_next = axi_word_count_next & OFFSET_MASK;
                end
                axi_cmd_last_transfer_next = op_word_count_next == 0;
                axi_cmd_valid_next = 1'b1;

                read_state_next = READ_STATE_REQ;
            end else begin
                read_state_next = READ_STATE_START;
            end
        end
        READ_STATE_REQ: begin
            // request state - issue AXI read requests
            if (!m_axi_arvalid) begin
                if (axi_word_count_reg <= AXI_MAX_BURST_SIZE - (read_addr_reg & OFFSET_MASK)) begin
                    // packet smaller than max burst size
                    if (read_addr_reg[12] != read_addr_plus_axi_count[12]) begin
                        // crosses 4k boundary
                        tr_word_count_next = 13'h1000 - read_addr_reg[11:0];
                    end else begin
                        // does not cross 4k boundary
                        tr_word_count_next = axi_word_count_reg;
                    end
                end else begin
                    // packet larger than max burst size
                    if (read_addr_reg[12] != read_addr_plus_max_burst[12]) begin
                        // crosses 4k boundary
                        tr_word_count_next = 13'h1000 - read_addr_reg[11:0];
                    end else begin
                        // does not cross 4k boundary
                        tr_word_count_next = AXI_MAX_BURST_SIZE - (read_addr_reg & OFFSET_MASK);
                    end
                end

                m_axi_araddr_next = read_addr_reg;
                if (ENABLE_UNALIGNED) begin
                    m_axi_arlen_next = (tr_word_count_next + (read_addr_reg & OFFSET_MASK) - 1) >> AXI_BURST_SIZE;
                end else begin
                    m_axi_arlen_next = (tr_word_count_next - 1) >> AXI_BURST_SIZE;
                end
                m_axi_arvalid_next = 1'b1;

                read_addr_next = read_addr_reg + tr_word_count_next;
                axi_word_count_next = axi_word_count_reg - tr_word_count_next;

                if (axi_word_count_next > 0) begin
                    read_state_next = READ_STATE_REQ;
                end else if (op_word_count_next > 0) begin
                    read_state_next = READ_STATE_START;
                end else begin
                    s_axis_desc_ready_next = !axi_cmd_valid_reg && enable;
                    read_state_next = READ_STATE_IDLE;
                end
            end else begin
                read_state_next = READ_STATE_REQ;
            end
        end
    endcase
end

always @* begin
    axi_state_next = AXI_STATE_IDLE;

    m_axis_desc_status_tag_next = m_axis_desc_status_tag_reg;
    m_axis_desc_status_valid_next = 1'b0;

    m_axi_awaddr_next = m_axi_awaddr_reg;
    m_axi_awlen_next = m_axi_awlen_reg;
    m_axi_awvalid_next = m_axi_awvalid_reg && !m_axi_awready;
    m_axi_wdata_int = shift_axi_rdata;
    m_axi_wstrb_int = {AXI_STRB_WIDTH{1'b0}};
    m_axi_wlast_int = 1'b0;
    m_axi_wvalid_int = 1'b0;
    m_axi_bready_next = 1'b0;

    m_axi_rready_next = 1'b0;

    transfer_in_save = 1'b0;
    axi_cmd_ready = 1'b0;
    status_fifo_we = 1'b0;

    offset_next = offset_reg;
    first_cycle_offset_next = first_cycle_offset_reg;
    last_cycle_offset_next = last_cycle_offset_reg;
    input_cycle_count_next = input_cycle_count_reg;
    output_cycle_count_next = output_cycle_count_reg;
    input_active_next = input_active_reg;
    output_active_next = output_active_reg;
    bubble_cycle_next = bubble_cycle_reg;
    first_input_cycle_next = first_input_cycle_reg;
    first_output_cycle_next = first_output_cycle_reg;
    output_last_cycle_next = output_last_cycle_reg;
    last_transfer_next = last_transfer_reg;

    tag_next = tag_reg;

    status_fifo_rd_ptr_next = status_fifo_rd_ptr_reg;

    status_fifo_wr_tag = tag_reg;
    status_fifo_wr_last = 1'b0;

    case (axi_state_reg)
        AXI_STATE_IDLE: begin
            // idle state - load new descriptor to start operation
            m_axi_rready_next = 1'b0;

            // store transfer parameters
            if (ENABLE_UNALIGNED) begin
                offset_next = axi_cmd_offset_reg;
                first_cycle_offset_next = axi_cmd_first_cycle_offset_reg;
            end else begin
                offset_next = 0;
                first_cycle_offset_next = 0;
            end
            last_cycle_offset_next = axi_cmd_last_cycle_offset_reg;
            input_cycle_count_next = axi_cmd_input_cycle_count_reg;
            output_cycle_count_next = axi_cmd_output_cycle_count_reg;
            bubble_cycle_next = axi_cmd_bubble_cycle_reg;
            last_transfer_next = axi_cmd_last_transfer_reg;
            tag_next = axi_cmd_tag_reg;

            output_last_cycle_next = output_cycle_count_next == 0;
            input_active_next = 1'b1;
            output_active_next = 1'b1;
            first_input_cycle_next = 1'b1;
            first_output_cycle_next = 1'b1;

            if (!m_axi_awvalid && axi_cmd_valid_reg) begin
                axi_cmd_ready = 1'b1;

                m_axi_awaddr_next = axi_cmd_addr_reg;
                m_axi_awlen_next = axi_cmd_output_cycle_count_reg;
                m_axi_awvalid_next = 1'b1;

                m_axi_rready_next = m_axi_wready_int_early;
                axi_state_next = AXI_STATE_WRITE;
            end
        end
        AXI_STATE_WRITE: begin
            // handle AXI read data
            m_axi_rready_next = m_axi_wready_int_early && input_active_reg;

            if (m_axi_wready_int_reg && ((m_axi_rready && m_axi_rvalid) || !input_active_reg)) begin
                // transfer in AXI read data
                transfer_in_save = m_axi_rready && m_axi_rvalid;

                if (ENABLE_UNALIGNED && first_input_cycle_reg && bubble_cycle_reg) begin
                    if (input_active_reg) begin
                        input_cycle_count_next = input_cycle_count_reg - 1;
                        input_active_next = input_cycle_count_reg > 0;
                    end
                    bubble_cycle_next = 1'b0;
                    first_input_cycle_next = 1'b0;

                    m_axi_rready_next = m_axi_wready_int_early && input_active_next;
                    axi_state_next = AXI_STATE_WRITE;
                end else begin
                    // update counters
                    if (input_active_reg) begin
                        input_cycle_count_next = input_cycle_count_reg - 1;
                        input_active_next = input_cycle_count_reg > 0;
                    end
                    if (output_active_reg) begin
                        output_cycle_count_next = output_cycle_count_reg - 1;
                        output_active_next = output_cycle_count_reg > 0;
                    end
                    output_last_cycle_next = output_cycle_count_next == 0;
                    bubble_cycle_next = 1'b0;
                    first_input_cycle_next = 1'b0;
                    first_output_cycle_next = 1'b0;

                    // pass through read data
                    m_axi_wdata_int = shift_axi_rdata;
                    if (first_output_cycle_reg) begin
                        m_axi_wstrb_int = {AXI_STRB_WIDTH{1'b1}} << first_cycle_offset_reg;
                    end else begin
                        m_axi_wstrb_int = {AXI_STRB_WIDTH{1'b1}};
                    end
                    m_axi_wvalid_int = 1'b1;

                    if (output_last_cycle_reg) begin
                        // no more data to transfer, finish operation
                        if (last_cycle_offset_reg > 0) begin
                            m_axi_wstrb_int = m_axi_wstrb_int & {AXI_STRB_WIDTH{1'b1}} >> (AXI_STRB_WIDTH - last_cycle_offset_reg);
                        end
                        m_axi_wlast_int = 1'b1;

                        status_fifo_we = 1'b1;
                        status_fifo_wr_tag = tag_reg;
                        status_fifo_wr_last = last_transfer_reg;

                        m_axi_rready_next = 1'b0;
                        axi_state_next = AXI_STATE_IDLE;
                    end else begin
                        // more cycles in AXI transfer
                        axi_state_next = AXI_STATE_WRITE;
                    end
                end
            end else begin
                axi_state_next = AXI_STATE_WRITE;
            end
        end
    endcase

    if (status_fifo_rd_ptr_reg != status_fifo_wr_ptr_reg) begin
        // status FIFO not empty
        if (m_axi_bready && m_axi_bvalid) begin
            // got write completion, pop and return status
            m_axis_desc_status_tag_next = status_fifo_tag[status_fifo_rd_ptr_reg[STATUS_FIFO_ADDR_WIDTH-1:0]];
            m_axis_desc_status_valid_next = status_fifo_last[status_fifo_rd_ptr_reg[STATUS_FIFO_ADDR_WIDTH-1:0]];
            status_fifo_rd_ptr_next = status_fifo_rd_ptr_reg + 1;
            m_axi_bready_next = 1'b0;
        end else begin
            // wait for write completion
            m_axi_bready_next = 1'b1;
        end
    end
end

always @(posedge clk) begin
    if (rst) begin
        read_state_reg <= READ_STATE_IDLE;
        axi_state_reg <= AXI_STATE_IDLE;
        axi_cmd_valid_reg <= 1'b0;
        s_axis_desc_ready_reg <= 1'b0;
        m_axis_desc_status_valid_reg <= 1'b0;
        m_axi_awvalid_reg <= 1'b0;
        m_axi_bready_reg <= 1'b0;
        m_axi_arvalid_reg <= 1'b0;
        m_axi_rready_reg <= 1'b0;

        status_fifo_wr_ptr_reg <= 0;
        status_fifo_rd_ptr_reg <= 0;
    end else begin
        read_state_reg <= read_state_next;
        axi_state_reg <= axi_state_next;
        axi_cmd_valid_reg <= axi_cmd_valid_next;
        s_axis_desc_ready_reg <= s_axis_desc_ready_next;
        m_axis_desc_status_valid_reg <= m_axis_desc_status_valid_next;
        m_axi_awvalid_reg <= m_axi_awvalid_next;
        m_axi_bready_reg <= m_axi_bready_next;
        m_axi_arvalid_reg <= m_axi_arvalid_next;
        m_axi_rready_reg <= m_axi_rready_next;

        if (status_fifo_we) begin
            status_fifo_wr_ptr_reg <= status_fifo_wr_ptr_reg + 1;
        end
        status_fifo_rd_ptr_reg <= status_fifo_rd_ptr_next;
    end

    m_axis_desc_status_tag_reg <= m_axis_desc_status_tag_next;

    m_axi_awaddr_reg <= m_axi_awaddr_next;
    m_axi_awlen_reg <= m_axi_awlen_next;
    m_axi_araddr_reg <= m_axi_araddr_next;
    m_axi_arlen_reg <= m_axi_arlen_next;

    read_addr_reg <= read_addr_next;
    write_addr_reg <= write_addr_next;
    op_word_count_reg <= op_word_count_next;
    tr_word_count_reg <= tr_word_count_next;
    axi_word_count_reg <= axi_word_count_next;

    axi_cmd_addr_reg <= axi_cmd_addr_next;
    axi_cmd_offset_reg <= axi_cmd_offset_next;
    axi_cmd_first_cycle_offset_reg <= axi_cmd_first_cycle_offset_next;
    axi_cmd_last_cycle_offset_reg <= axi_cmd_last_cycle_offset_next;
    axi_cmd_input_cycle_count_reg <= axi_cmd_input_cycle_count_next;
    axi_cmd_output_cycle_count_reg <= axi_cmd_output_cycle_count_next;
    axi_cmd_bubble_cycle_reg <= axi_cmd_bubble_cycle_next;
    axi_cmd_last_transfer_reg <= axi_cmd_last_transfer_next;
    axi_cmd_tag_reg <= axi_cmd_tag_next;
    axi_cmd_valid_reg <= axi_cmd_valid_next;

    offset_reg <= offset_next;
    first_cycle_offset_reg <= first_cycle_offset_next;
    last_cycle_offset_reg <= last_cycle_offset_next;
    input_cycle_count_reg <= input_cycle_count_next;
    output_cycle_count_reg <= output_cycle_count_next;
    input_active_reg <= input_active_next;
    output_active_reg <= output_active_next;
    bubble_cycle_reg <= bubble_cycle_next;
    first_input_cycle_reg <= first_input_cycle_next;
    first_output_cycle_reg <= first_output_cycle_next;
    output_last_cycle_reg <= output_last_cycle_next;
    last_transfer_reg <= last_transfer_next;

    tag_reg <= tag_next;

    if (transfer_in_save) begin
        save_axi_rdata_reg <= m_axi_rdata;
    end

    if (status_fifo_we) begin
        status_fifo_tag[status_fifo_wr_ptr_reg[STATUS_FIFO_ADDR_WIDTH-1:0]] <= status_fifo_wr_tag;
        status_fifo_last[status_fifo_wr_ptr_reg[STATUS_FIFO_ADDR_WIDTH-1:0]] <= status_fifo_wr_last;
        status_fifo_wr_ptr_reg <= status_fifo_wr_ptr_reg + 1;
    end
end

// output datapath logic
reg [AXI_DATA_WIDTH-1:0] m_axi_wdata_reg  = {AXI_DATA_WIDTH{1'b0}};
reg [AXI_STRB_WIDTH-1:0] m_axi_wstrb_reg  = {AXI_STRB_WIDTH{1'b0}};
reg                      m_axi_wlast_reg  = 1'b0;
reg                      m_axi_wvalid_reg = 1'b0, m_axi_wvalid_next;

reg [AXI_DATA_WIDTH-1:0] temp_m_axi_wdata_reg  = {AXI_DATA_WIDTH{1'b0}};
reg [AXI_STRB_WIDTH-1:0] temp_m_axi_wstrb_reg  = {AXI_STRB_WIDTH{1'b0}};
reg                      temp_m_axi_wlast_reg  = 1'b0;
reg                      temp_m_axi_wvalid_reg = 1'b0, temp_m_axi_wvalid_next;

// datapath control
reg store_axi_w_int_to_output;
reg store_axi_w_int_to_temp;
reg store_axi_w_temp_to_output;

assign m_axi_wdata  = m_axi_wdata_reg;
assign m_axi_wstrb  = m_axi_wstrb_reg;
assign m_axi_wvalid = m_axi_wvalid_reg;
assign m_axi_wlast  = m_axi_wlast_reg;

// enable ready input next cycle if output is ready or the temp reg will not be filled on the next cycle (output reg empty or no input)
assign m_axi_wready_int_early = m_axi_wready || (!temp_m_axi_wvalid_reg && (!m_axi_wvalid_reg || !m_axi_wvalid_int));

always @* begin
    // transfer sink ready state to source
    m_axi_wvalid_next = m_axi_wvalid_reg;
    temp_m_axi_wvalid_next = temp_m_axi_wvalid_reg;

    store_axi_w_int_to_output = 1'b0;
    store_axi_w_int_to_temp = 1'b0;
    store_axi_w_temp_to_output = 1'b0;

    if (m_axi_wready_int_reg) begin
        // input is ready
        if (m_axi_wready || !m_axi_wvalid_reg) begin
            // output is ready or currently not valid, transfer data to output
            m_axi_wvalid_next = m_axi_wvalid_int;
            store_axi_w_int_to_output = 1'b1;
        end else begin
            // output is not ready, store input in temp
            temp_m_axi_wvalid_next = m_axi_wvalid_int;
            store_axi_w_int_to_temp = 1'b1;
        end
    end else if (m_axi_wready) begin
        // input is not ready, but output is ready
        m_axi_wvalid_next = temp_m_axi_wvalid_reg;
        temp_m_axi_wvalid_next = 1'b0;
        store_axi_w_temp_to_output = 1'b1;
    end
end

always @(posedge clk) begin
    if (rst) begin
        m_axi_wvalid_reg <= 1'b0;
        m_axi_wready_int_reg <= 1'b0;
        temp_m_axi_wvalid_reg <= 1'b0;
    end else begin
        m_axi_wvalid_reg <= m_axi_wvalid_next;
        m_axi_wready_int_reg <= m_axi_wready_int_early;
        temp_m_axi_wvalid_reg <= temp_m_axi_wvalid_next;
    end

    // datapath
    if (store_axi_w_int_to_output) begin
        m_axi_wdata_reg <= m_axi_wdata_int;
        m_axi_wstrb_reg <= m_axi_wstrb_int;
        m_axi_wlast_reg <= m_axi_wlast_int;
    end else if (store_axi_w_temp_to_output) begin
        m_axi_wdata_reg <= temp_m_axi_wdata_reg;
        m_axi_wstrb_reg <= temp_m_axi_wstrb_reg;
        m_axi_wlast_reg <= temp_m_axi_wlast_reg;
    end

    if (store_axi_w_int_to_temp) begin
        temp_m_axi_wdata_reg <= m_axi_wdata_int;
        temp_m_axi_wstrb_reg <= m_axi_wstrb_int;
        temp_m_axi_wlast_reg <= m_axi_wlast_int;
    end
end

endmodule