module axi_dma_rd #
(
    // Width of AXI data bus in bits
    parameter AXI_DATA_WIDTH = 32,
    // Width of AXI address bus in bits
    parameter AXI_ADDR_WIDTH = 16,
    // Width of AXI 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 AXI stream interfaces in bits
    parameter AXIS_DATA_WIDTH = AXI_DATA_WIDTH,
    // Use AXI stream tkeep signal
    parameter AXIS_KEEP_ENABLE = (AXIS_DATA_WIDTH>8),
    // AXI stream tkeep signal width (words per cycle)
    parameter AXIS_KEEP_WIDTH = (AXIS_DATA_WIDTH/8),
    // Use AXI stream tlast signal
    parameter AXIS_LAST_ENABLE = 1,
    // Propagate AXI stream tid signal
    parameter AXIS_ID_ENABLE = 0,
    // AXI stream tid signal width
    parameter AXIS_ID_WIDTH = 8,
    // Propagate AXI stream tdest signal
    parameter AXIS_DEST_ENABLE = 0,
    // AXI stream tdest signal width
    parameter AXIS_DEST_WIDTH = 8,
    // Propagate AXI stream tuser signal
    parameter AXIS_USER_ENABLE = 1,
    // AXI stream tuser signal width
    parameter AXIS_USER_WIDTH = 1,
    // Width of length field
    parameter LEN_WIDTH = 20,
    // Width of tag field
    parameter TAG_WIDTH = 8,
    // Enable support for scatter/gather DMA
    // (multiple descriptors per AXI stream frame)
    parameter ENABLE_SG = 0,
    // Enable support for unaligned transfers
    parameter ENABLE_UNALIGNED = 0
)
(
    input  wire                       clk,
    input  wire                       rst,

    /*
     * AXI read descriptor input
     */
    input  wire [AXI_ADDR_WIDTH-1:0]  s_axis_read_desc_addr,
    input  wire [LEN_WIDTH-1:0]       s_axis_read_desc_len,
    input  wire [TAG_WIDTH-1:0]       s_axis_read_desc_tag,
    input  wire [AXIS_ID_WIDTH-1:0]   s_axis_read_desc_id,
    input  wire [AXIS_DEST_WIDTH-1:0] s_axis_read_desc_dest,
    input  wire [AXIS_USER_WIDTH-1:0] s_axis_read_desc_user,
    input  wire                       s_axis_read_desc_valid,
    output wire                       s_axis_read_desc_ready,

    /*
     * AXI read descriptor status output
     */
    output wire [TAG_WIDTH-1:0]       m_axis_read_desc_status_tag,
    output wire [3:0]                 m_axis_read_desc_status_error,
    output wire                       m_axis_read_desc_status_valid,

    /*
     * AXI stream read data output
     */
    output wire [AXIS_DATA_WIDTH-1:0] m_axis_read_data_tdata,
    output wire [AXIS_KEEP_WIDTH-1:0] m_axis_read_data_tkeep,
    output wire                       m_axis_read_data_tvalid,
    input  wire                       m_axis_read_data_tready,
    output wire                       m_axis_read_data_tlast,
    output wire [AXIS_ID_WIDTH-1:0]   m_axis_read_data_tid,
    output wire [AXIS_DEST_WIDTH-1:0] m_axis_read_data_tdest,
    output wire [AXIS_USER_WIDTH-1:0] m_axis_read_data_tuser,

    /*
     * AXI 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 AXIS_KEEP_WIDTH_INT = AXIS_KEEP_ENABLE ? AXIS_KEEP_WIDTH : 1;
parameter AXIS_WORD_WIDTH = AXIS_KEEP_WIDTH_INT;
parameter AXIS_WORD_SIZE = AXIS_DATA_WIDTH/AXIS_WORD_WIDTH;

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 OUTPUT_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 (AXIS_WORD_SIZE * AXIS_KEEP_WIDTH_INT != AXIS_DATA_WIDTH) begin
        $error("Error: AXI stream data width not evenly divisble (instance %m)");
        $finish;
    end

    if (AXI_WORD_SIZE != AXIS_WORD_SIZE) begin
        $error("Error: word size mismatch (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_DATA_WIDTH != AXIS_DATA_WIDTH) begin
        $error("Error: AXI interface width must match AXI stream interface width (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

    if (ENABLE_SG) begin
        $error("Error: scatter/gather is not yet implemented (instance %m)");
        $finish;
    end
end

localparam [1:0]
    AXI_RESP_OKAY = 2'b00,
    AXI_RESP_EXOKAY = 2'b01,
    AXI_RESP_SLVERR = 2'b10,
    AXI_RESP_DECERR = 2'b11;

localparam [3:0]
    DMA_ERROR_NONE = 4'd0,
    DMA_ERROR_TIMEOUT = 4'd1,
    DMA_ERROR_PARITY = 4'd2,
    DMA_ERROR_AXI_RD_SLVERR = 4'd4,
    DMA_ERROR_AXI_RD_DECERR = 4'd5,
    DMA_ERROR_AXI_WR_SLVERR = 4'd6,
    DMA_ERROR_AXI_WR_DECERR = 4'd7,
    DMA_ERROR_PCIE_FLR = 4'd8,
    DMA_ERROR_PCIE_CPL_POISONED = 4'd9,
    DMA_ERROR_PCIE_CPL_STATUS_UR = 4'd10,
    DMA_ERROR_PCIE_CPL_STATUS_CA = 4'd11;

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

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

localparam [0:0]
    AXIS_STATE_IDLE = 1'd0,
    AXIS_STATE_READ = 1'd1;

reg [0:0] axis_state_reg = AXIS_STATE_IDLE, axis_state_next;

// datapath control signals
reg transfer_in_save;
reg axis_cmd_ready;

reg [AXI_ADDR_WIDTH-1:0] addr_reg = {AXI_ADDR_WIDTH{1'b0}}, 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 [OFFSET_WIDTH-1:0] axis_cmd_offset_reg = {OFFSET_WIDTH{1'b0}}, axis_cmd_offset_next;
reg [OFFSET_WIDTH-1:0] axis_cmd_last_cycle_offset_reg = {OFFSET_WIDTH{1'b0}}, axis_cmd_last_cycle_offset_next;
reg [CYCLE_COUNT_WIDTH-1:0] axis_cmd_input_cycle_count_reg = {CYCLE_COUNT_WIDTH{1'b0}}, axis_cmd_input_cycle_count_next;
reg [CYCLE_COUNT_WIDTH-1:0] axis_cmd_output_cycle_count_reg = {CYCLE_COUNT_WIDTH{1'b0}}, axis_cmd_output_cycle_count_next;
reg axis_cmd_bubble_cycle_reg = 1'b0, axis_cmd_bubble_cycle_next;
reg [TAG_WIDTH-1:0] axis_cmd_tag_reg = {TAG_WIDTH{1'b0}}, axis_cmd_tag_next;
reg [AXIS_ID_WIDTH-1:0] axis_cmd_axis_id_reg = {AXIS_ID_WIDTH{1'b0}}, axis_cmd_axis_id_next;
reg [AXIS_DEST_WIDTH-1:0] axis_cmd_axis_dest_reg = {AXIS_DEST_WIDTH{1'b0}}, axis_cmd_axis_dest_next;
reg [AXIS_USER_WIDTH-1:0] axis_cmd_axis_user_reg = {AXIS_USER_WIDTH{1'b0}}, axis_cmd_axis_user_next;
reg axis_cmd_valid_reg = 1'b0, axis_cmd_valid_next;

reg [OFFSET_WIDTH-1:0] offset_reg = {OFFSET_WIDTH{1'b0}}, 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_cycle_reg = 1'b0, first_cycle_next;
reg output_last_cycle_reg = 1'b0, output_last_cycle_next;
reg [1:0] rresp_reg = AXI_RESP_OKAY, rresp_next;

reg [TAG_WIDTH-1:0] tag_reg = {TAG_WIDTH{1'b0}}, tag_next;
reg [AXIS_ID_WIDTH-1:0] axis_id_reg = {AXIS_ID_WIDTH{1'b0}}, axis_id_next;
reg [AXIS_DEST_WIDTH-1:0] axis_dest_reg = {AXIS_DEST_WIDTH{1'b0}}, axis_dest_next;
reg [AXIS_USER_WIDTH-1:0] axis_user_reg = {AXIS_USER_WIDTH{1'b0}}, axis_user_next;

reg s_axis_read_desc_ready_reg = 1'b0, s_axis_read_desc_ready_next;

reg [TAG_WIDTH-1:0] m_axis_read_desc_status_tag_reg = {TAG_WIDTH{1'b0}}, m_axis_read_desc_status_tag_next;
reg [3:0] m_axis_read_desc_status_error_reg = 4'd0, m_axis_read_desc_status_error_next;
reg m_axis_read_desc_status_valid_reg = 1'b0, m_axis_read_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_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  [AXIS_DATA_WIDTH-1:0] m_axis_read_data_tdata_int;
reg  [AXIS_KEEP_WIDTH-1:0] m_axis_read_data_tkeep_int;
reg                        m_axis_read_data_tvalid_int;
wire                       m_axis_read_data_tready_int;
reg                        m_axis_read_data_tlast_int;
reg  [AXIS_ID_WIDTH-1:0]   m_axis_read_data_tid_int;
reg  [AXIS_DEST_WIDTH-1:0] m_axis_read_data_tdest_int;
reg  [AXIS_USER_WIDTH-1:0] m_axis_read_data_tuser_int;

assign s_axis_read_desc_ready = s_axis_read_desc_ready_reg;

assign m_axis_read_desc_status_tag = m_axis_read_desc_status_tag_reg;
assign m_axis_read_desc_status_error = m_axis_read_desc_status_error_reg;
assign m_axis_read_desc_status_valid = m_axis_read_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;

always @* begin
    axi_state_next = AXI_STATE_IDLE;

    s_axis_read_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;

    addr_next = addr_reg;
    op_word_count_next = op_word_count_reg;
    tr_word_count_next = tr_word_count_reg;

    axis_cmd_offset_next = axis_cmd_offset_reg;
    axis_cmd_last_cycle_offset_next = axis_cmd_last_cycle_offset_reg;
    axis_cmd_input_cycle_count_next = axis_cmd_input_cycle_count_reg;
    axis_cmd_output_cycle_count_next = axis_cmd_output_cycle_count_reg;
    axis_cmd_bubble_cycle_next = axis_cmd_bubble_cycle_reg;
    axis_cmd_tag_next = axis_cmd_tag_reg;
    axis_cmd_axis_id_next = axis_cmd_axis_id_reg;
    axis_cmd_axis_dest_next = axis_cmd_axis_dest_reg;
    axis_cmd_axis_user_next = axis_cmd_axis_user_reg;
    axis_cmd_valid_next = axis_cmd_valid_reg && !axis_cmd_ready;

    case (axi_state_reg)
        AXI_STATE_IDLE: begin
            // idle state - load new descriptor to start operation
            s_axis_read_desc_ready_next = !axis_cmd_valid_reg && enable;

            if (s_axis_read_desc_ready && s_axis_read_desc_valid) begin
                if (ENABLE_UNALIGNED) begin
                    addr_next = s_axis_read_desc_addr;
                    axis_cmd_offset_next = AXI_STRB_WIDTH > 1 ? AXI_STRB_WIDTH - (s_axis_read_desc_addr & OFFSET_MASK) : 0;
                    axis_cmd_bubble_cycle_next = axis_cmd_offset_next > 0;
                    axis_cmd_last_cycle_offset_next = s_axis_read_desc_len & OFFSET_MASK;
                end else begin
                    addr_next = s_axis_read_desc_addr & ADDR_MASK;
                    axis_cmd_offset_next = 0;
                    axis_cmd_bubble_cycle_next = 1'b0;
                    axis_cmd_last_cycle_offset_next = s_axis_read_desc_len & OFFSET_MASK;
                end
                axis_cmd_tag_next = s_axis_read_desc_tag;
                op_word_count_next = s_axis_read_desc_len;

                axis_cmd_axis_id_next = s_axis_read_desc_id;
                axis_cmd_axis_dest_next = s_axis_read_desc_dest;
                axis_cmd_axis_user_next = s_axis_read_desc_user;

                if (ENABLE_UNALIGNED) begin
                    axis_cmd_input_cycle_count_next = (op_word_count_next + (s_axis_read_desc_addr & OFFSET_MASK) - 1) >> AXI_BURST_SIZE;
                end else begin
                    axis_cmd_input_cycle_count_next = (op_word_count_next - 1) >> AXI_BURST_SIZE;
                end
                axis_cmd_output_cycle_count_next = (op_word_count_next - 1) >> AXI_BURST_SIZE;

                axis_cmd_valid_next = 1'b1;

                s_axis_read_desc_ready_next = 1'b0;
                axi_state_next = AXI_STATE_START;
            end else begin
                axi_state_next = AXI_STATE_IDLE;
            end
        end
        AXI_STATE_START: begin
            // start state - initiate new AXI transfer
            if (!m_axi_arvalid) begin
                if (op_word_count_reg <= AXI_MAX_BURST_SIZE - (addr_reg & OFFSET_MASK) || AXI_MAX_BURST_SIZE >= 4096) begin
                    // packet smaller than max burst size
                    if (((addr_reg & 12'hfff) + (op_word_count_reg & 12'hfff)) >> 12 != 0 || op_word_count_reg >> 12 != 0) begin
                        // crosses 4k boundary
                        tr_word_count_next = 13'h1000 - (addr_reg & 12'hfff);
                    end else begin
                        // does not cross 4k boundary
                        tr_word_count_next = op_word_count_reg;
                    end
                end else begin
                    // packet larger than max burst size
                    if (((addr_reg & 12'hfff) + AXI_MAX_BURST_SIZE) >> 12 != 0) begin
                        // crosses 4k boundary
                        tr_word_count_next = 13'h1000 - (addr_reg & 12'hfff);
                    end else begin
                        // does not cross 4k boundary
                        tr_word_count_next = AXI_MAX_BURST_SIZE - (addr_reg & OFFSET_MASK);
                    end
                end

                m_axi_araddr_next = addr_reg;
                if (ENABLE_UNALIGNED) begin
                    m_axi_arlen_next = (tr_word_count_next + (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;

                addr_next = addr_reg + tr_word_count_next;
                op_word_count_next = op_word_count_reg - tr_word_count_next;

                if (op_word_count_next > 0) begin
                    axi_state_next = AXI_STATE_START;
                end else begin
                    s_axis_read_desc_ready_next = !axis_cmd_valid_reg && enable;
                    axi_state_next = AXI_STATE_IDLE;
                end
            end else begin
                axi_state_next = AXI_STATE_START;
            end
        end
    endcase
end

always @* begin
    axis_state_next = AXIS_STATE_IDLE;

    m_axis_read_desc_status_tag_next = m_axis_read_desc_status_tag_reg;
    m_axis_read_desc_status_error_next = m_axis_read_desc_status_error_reg;
    m_axis_read_desc_status_valid_next = 1'b0;

    m_axis_read_data_tdata_int = shift_axi_rdata;
    m_axis_read_data_tkeep_int = {AXIS_KEEP_WIDTH{1'b1}};
    m_axis_read_data_tlast_int = 1'b0;
    m_axis_read_data_tvalid_int = 1'b0;
    m_axis_read_data_tid_int = axis_id_reg;
    m_axis_read_data_tdest_int = axis_dest_reg;
    m_axis_read_data_tuser_int = axis_user_reg;

    m_axi_rready_next = 1'b0;

    transfer_in_save = 1'b0;
    axis_cmd_ready = 1'b0;

    offset_next = 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_cycle_next = first_cycle_reg;
    output_last_cycle_next = output_last_cycle_reg;

    tag_next = tag_reg;
    axis_id_next = axis_id_reg;
    axis_dest_next = axis_dest_reg;
    axis_user_next = axis_user_reg;

    if (m_axi_rready && m_axi_rvalid && (m_axi_rresp == AXI_RESP_SLVERR || m_axi_rresp == AXI_RESP_DECERR)) begin
        rresp_next = m_axi_rresp;
    end else begin
        rresp_next = rresp_reg;
    end

    case (axis_state_reg)
        AXIS_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 = axis_cmd_offset_reg;
            end else begin
                offset_next = 0;
            end
            last_cycle_offset_next = axis_cmd_last_cycle_offset_reg;
            input_cycle_count_next = axis_cmd_input_cycle_count_reg;
            output_cycle_count_next = axis_cmd_output_cycle_count_reg;
            bubble_cycle_next = axis_cmd_bubble_cycle_reg;
            tag_next = axis_cmd_tag_reg;
            axis_id_next = axis_cmd_axis_id_reg;
            axis_dest_next = axis_cmd_axis_dest_reg;
            axis_user_next = axis_cmd_axis_user_reg;

            output_last_cycle_next = output_cycle_count_next == 0;
            input_active_next = 1'b1;
            output_active_next = 1'b1;
            first_cycle_next = 1'b1;

            if (axis_cmd_valid_reg) begin
                axis_cmd_ready = 1'b1;
                m_axi_rready_next = m_axis_read_data_tready_int;
                axis_state_next = AXIS_STATE_READ;
            end
        end
        AXIS_STATE_READ: begin
            // handle AXI read data
            m_axi_rready_next = m_axis_read_data_tready_int && input_active_reg;

            if ((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_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_cycle_next = 1'b0;

                    m_axi_rready_next = m_axis_read_data_tready_int && input_active_next;
                    axis_state_next = AXIS_STATE_READ;
                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_cycle_next = 1'b0;

                    // pass through read data
                    m_axis_read_data_tdata_int = shift_axi_rdata;
                    m_axis_read_data_tkeep_int = {AXIS_KEEP_WIDTH_INT{1'b1}};
                    m_axis_read_data_tvalid_int = 1'b1;

                    if (output_last_cycle_reg) begin
                        // no more data to transfer, finish operation
                        if (last_cycle_offset_reg > 0) begin
                            m_axis_read_data_tkeep_int = {AXIS_KEEP_WIDTH_INT{1'b1}} >> (AXIS_KEEP_WIDTH_INT - last_cycle_offset_reg);
                        end
                        m_axis_read_data_tlast_int = 1'b1;

                        m_axis_read_desc_status_tag_next = tag_reg;
                        if (rresp_next == AXI_RESP_SLVERR) begin
                            m_axis_read_desc_status_error_next = DMA_ERROR_AXI_RD_SLVERR;
                        end else if (rresp_next == AXI_RESP_DECERR) begin
                            m_axis_read_desc_status_error_next = DMA_ERROR_AXI_RD_DECERR;
                        end else begin
                            m_axis_read_desc_status_error_next = DMA_ERROR_NONE;
                        end
                        m_axis_read_desc_status_valid_next = 1'b1;

                        rresp_next = AXI_RESP_OKAY;

                        m_axi_rready_next = 1'b0;
                        axis_state_next = AXIS_STATE_IDLE;
                    end else begin
                        // more cycles in AXI transfer
                        m_axi_rready_next = m_axis_read_data_tready_int && input_active_next;
                        axis_state_next = AXIS_STATE_READ;
                    end
                end
            end else begin
                axis_state_next = AXIS_STATE_READ;
            end
        end
    endcase
end

always @(posedge clk) begin
    axi_state_reg <= axi_state_next;
    axis_state_reg <= axis_state_next;

    s_axis_read_desc_ready_reg <= s_axis_read_desc_ready_next;

    m_axis_read_desc_status_tag_reg <= m_axis_read_desc_status_tag_next;
    m_axis_read_desc_status_error_reg <= m_axis_read_desc_status_error_next;
    m_axis_read_desc_status_valid_reg <= m_axis_read_desc_status_valid_next;

    m_axi_araddr_reg <= m_axi_araddr_next;
    m_axi_arlen_reg <= m_axi_arlen_next;
    m_axi_arvalid_reg <= m_axi_arvalid_next;
    m_axi_rready_reg <= m_axi_rready_next;

    addr_reg <= addr_next;
    op_word_count_reg <= op_word_count_next;
    tr_word_count_reg <= tr_word_count_next;

    axis_cmd_offset_reg <= axis_cmd_offset_next;
    axis_cmd_last_cycle_offset_reg <= axis_cmd_last_cycle_offset_next;
    axis_cmd_input_cycle_count_reg <= axis_cmd_input_cycle_count_next;
    axis_cmd_output_cycle_count_reg <= axis_cmd_output_cycle_count_next;
    axis_cmd_bubble_cycle_reg <= axis_cmd_bubble_cycle_next;
    axis_cmd_tag_reg <= axis_cmd_tag_next;
    axis_cmd_axis_id_reg <= axis_cmd_axis_id_next;
    axis_cmd_axis_dest_reg <= axis_cmd_axis_dest_next;
    axis_cmd_axis_user_reg <= axis_cmd_axis_user_next;
    axis_cmd_valid_reg <= axis_cmd_valid_next;

    offset_reg <= 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_cycle_reg <= first_cycle_next;
    output_last_cycle_reg <= output_last_cycle_next;
    rresp_reg <= rresp_next;

    tag_reg <= tag_next;
    axis_id_reg <= axis_id_next;
    axis_dest_reg <= axis_dest_next;
    axis_user_reg <= axis_user_next;

    if (transfer_in_save) begin
        save_axi_rdata_reg <= m_axi_rdata;
    end

    if (rst) begin
        axi_state_reg <= AXI_STATE_IDLE;
        axis_state_reg <= AXIS_STATE_IDLE;

        axis_cmd_valid_reg <= 1'b0;

        s_axis_read_desc_ready_reg <= 1'b0;

        m_axis_read_desc_status_valid_reg <= 1'b0;
        m_axi_arvalid_reg <= 1'b0;
        m_axi_rready_reg <= 1'b0;

        rresp_reg <= AXI_RESP_OKAY;
    end
end

// output datapath logic
reg [AXIS_DATA_WIDTH-1:0] m_axis_read_data_tdata_reg  = {AXIS_DATA_WIDTH{1'b0}};
reg [AXIS_KEEP_WIDTH-1:0] m_axis_read_data_tkeep_reg  = {AXIS_KEEP_WIDTH{1'b0}};
reg                       m_axis_read_data_tvalid_reg = 1'b0;
reg                       m_axis_read_data_tlast_reg  = 1'b0;
reg [AXIS_ID_WIDTH-1:0]   m_axis_read_data_tid_reg    = {AXIS_ID_WIDTH{1'b0}};
reg [AXIS_DEST_WIDTH-1:0] m_axis_read_data_tdest_reg  = {AXIS_DEST_WIDTH{1'b0}};
reg [AXIS_USER_WIDTH-1:0] m_axis_read_data_tuser_reg  = {AXIS_USER_WIDTH{1'b0}};

reg [OUTPUT_FIFO_ADDR_WIDTH+1-1:0] out_fifo_wr_ptr_reg = 0;
reg [OUTPUT_FIFO_ADDR_WIDTH+1-1:0] out_fifo_rd_ptr_reg = 0;
reg out_fifo_half_full_reg = 1'b0;

wire out_fifo_full = out_fifo_wr_ptr_reg == (out_fifo_rd_ptr_reg ^ {1'b1, {OUTPUT_FIFO_ADDR_WIDTH{1'b0}}});
wire out_fifo_empty = out_fifo_wr_ptr_reg == out_fifo_rd_ptr_reg;

(* ram_style = "distributed", ramstyle = "no_rw_check, mlab" *)
reg [AXIS_DATA_WIDTH-1:0] out_fifo_tdata[2**OUTPUT_FIFO_ADDR_WIDTH-1:0];
(* ram_style = "distributed", ramstyle = "no_rw_check, mlab" *)
reg [AXIS_KEEP_WIDTH-1:0] out_fifo_tkeep[2**OUTPUT_FIFO_ADDR_WIDTH-1:0];
(* ram_style = "distributed", ramstyle = "no_rw_check, mlab" *)
reg                       out_fifo_tlast[2**OUTPUT_FIFO_ADDR_WIDTH-1:0];
(* ram_style = "distributed", ramstyle = "no_rw_check, mlab" *)
reg [AXIS_ID_WIDTH-1:0]   out_fifo_tid[2**OUTPUT_FIFO_ADDR_WIDTH-1:0];
(* ram_style = "distributed", ramstyle = "no_rw_check, mlab" *)
reg [AXIS_DEST_WIDTH-1:0] out_fifo_tdest[2**OUTPUT_FIFO_ADDR_WIDTH-1:0];
(* ram_style = "distributed", ramstyle = "no_rw_check, mlab" *)
reg [AXIS_USER_WIDTH-1:0] out_fifo_tuser[2**OUTPUT_FIFO_ADDR_WIDTH-1:0];

assign m_axis_read_data_tready_int = !out_fifo_half_full_reg;

assign m_axis_read_data_tdata  = m_axis_read_data_tdata_reg;
assign m_axis_read_data_tkeep  = AXIS_KEEP_ENABLE ? m_axis_read_data_tkeep_reg : {AXIS_KEEP_WIDTH{1'b1}};
assign m_axis_read_data_tvalid = m_axis_read_data_tvalid_reg;
assign m_axis_read_data_tlast  = AXIS_LAST_ENABLE ? m_axis_read_data_tlast_reg : 1'b1;
assign m_axis_read_data_tid    = AXIS_ID_ENABLE   ? m_axis_read_data_tid_reg   : {AXIS_ID_WIDTH{1'b0}};
assign m_axis_read_data_tdest  = AXIS_DEST_ENABLE ? m_axis_read_data_tdest_reg : {AXIS_DEST_WIDTH{1'b0}};
assign m_axis_read_data_tuser  = AXIS_USER_ENABLE ? m_axis_read_data_tuser_reg : {AXIS_USER_WIDTH{1'b0}};

always @(posedge clk) begin
    m_axis_read_data_tvalid_reg <= m_axis_read_data_tvalid_reg && !m_axis_read_data_tready;

    out_fifo_half_full_reg <= $unsigned(out_fifo_wr_ptr_reg - out_fifo_rd_ptr_reg) >= 2**(OUTPUT_FIFO_ADDR_WIDTH-1);

    if (!out_fifo_full && m_axis_read_data_tvalid_int) begin
        out_fifo_tdata[out_fifo_wr_ptr_reg[OUTPUT_FIFO_ADDR_WIDTH-1:0]] <= m_axis_read_data_tdata_int;
        out_fifo_tkeep[out_fifo_wr_ptr_reg[OUTPUT_FIFO_ADDR_WIDTH-1:0]] <= m_axis_read_data_tkeep_int;
        out_fifo_tlast[out_fifo_wr_ptr_reg[OUTPUT_FIFO_ADDR_WIDTH-1:0]] <= m_axis_read_data_tlast_int;
        out_fifo_tid[out_fifo_wr_ptr_reg[OUTPUT_FIFO_ADDR_WIDTH-1:0]] <= m_axis_read_data_tid_int;
        out_fifo_tdest[out_fifo_wr_ptr_reg[OUTPUT_FIFO_ADDR_WIDTH-1:0]] <= m_axis_read_data_tdest_int;
        out_fifo_tuser[out_fifo_wr_ptr_reg[OUTPUT_FIFO_ADDR_WIDTH-1:0]] <= m_axis_read_data_tuser_int;
        out_fifo_wr_ptr_reg <= out_fifo_wr_ptr_reg + 1;
    end

    if (!out_fifo_empty && (!m_axis_read_data_tvalid_reg || m_axis_read_data_tready)) begin
        m_axis_read_data_tdata_reg <= out_fifo_tdata[out_fifo_rd_ptr_reg[OUTPUT_FIFO_ADDR_WIDTH-1:0]];
        m_axis_read_data_tkeep_reg <= out_fifo_tkeep[out_fifo_rd_ptr_reg[OUTPUT_FIFO_ADDR_WIDTH-1:0]];
        m_axis_read_data_tvalid_reg <= 1'b1;
        m_axis_read_data_tlast_reg <= out_fifo_tlast[out_fifo_rd_ptr_reg[OUTPUT_FIFO_ADDR_WIDTH-1:0]];
        m_axis_read_data_tid_reg <= out_fifo_tid[out_fifo_rd_ptr_reg[OUTPUT_FIFO_ADDR_WIDTH-1:0]];
        m_axis_read_data_tdest_reg <= out_fifo_tdest[out_fifo_rd_ptr_reg[OUTPUT_FIFO_ADDR_WIDTH-1:0]];
        m_axis_read_data_tuser_reg <= out_fifo_tuser[out_fifo_rd_ptr_reg[OUTPUT_FIFO_ADDR_WIDTH-1:0]];
        out_fifo_rd_ptr_reg <= out_fifo_rd_ptr_reg + 1;
    end

    if (rst) begin
        out_fifo_wr_ptr_reg <= 0;
        out_fifo_rd_ptr_reg <= 0;
        m_axis_read_data_tvalid_reg <= 1'b0;
    end
end

endmodule