module desc_fetch #
(
    // Number of ports
    parameter PORTS = 2,
    // Select field width
    parameter SELECT_WIDTH = $clog2(PORTS),
    // RAM segment count
    parameter SEG_COUNT = 2,
    // RAM segment data width
    parameter SEG_DATA_WIDTH = 64,
    // RAM segment address width
    parameter SEG_ADDR_WIDTH = 8,
    // RAM segment byte enable width
    parameter SEG_BE_WIDTH = SEG_DATA_WIDTH/8,
    // RAM address width
    parameter RAM_ADDR_WIDTH = SEG_ADDR_WIDTH+$clog2(SEG_COUNT)+$clog2(SEG_BE_WIDTH),
    // DMA RAM pipeline stages
    parameter RAM_PIPELINE = 2,
    // DMA address width
    parameter DMA_ADDR_WIDTH = 64,
    // DMA length field width
    parameter DMA_LEN_WIDTH = 20,
    // DMA tag field width
    parameter DMA_TAG_WIDTH = 8,
    // Transmit request tag field width
    parameter REQ_TAG_WIDTH = 8,
    // Queue request tag field width
    parameter QUEUE_REQ_TAG_WIDTH = 8,
    // Queue operation tag field width
    parameter QUEUE_OP_TAG_WIDTH = 8,
    // Queue index width
    parameter QUEUE_INDEX_WIDTH = 4,
    // Completion queue index width
    parameter CPL_QUEUE_INDEX_WIDTH = 4,
    // Queue element pointer width
    parameter QUEUE_PTR_WIDTH = 16,
    // Descriptor size (in bytes)
    parameter DESC_SIZE = 16,
    // Log desc block size field width
    parameter LOG_BLOCK_SIZE_WIDTH = 2,
    // Descriptor table size (number of in-flight operations)
    parameter DESC_TABLE_SIZE = 8,
    // Width of AXI stream interface in bits
    parameter AXIS_DATA_WIDTH = DESC_SIZE*8,
    // AXI stream tkeep signal width (words per cycle)
    parameter AXIS_KEEP_WIDTH = AXIS_DATA_WIDTH/8
)
(
    input  wire                                   clk,
    input  wire                                   rst,

    /*
     * Descriptor read request input
     */
    input  wire [SELECT_WIDTH-1:0]                s_axis_req_sel,
    input  wire [QUEUE_INDEX_WIDTH-1:0]           s_axis_req_queue,
    input  wire [REQ_TAG_WIDTH-1:0]               s_axis_req_tag,
    input  wire                                   s_axis_req_valid,
    output wire                                   s_axis_req_ready,

    /*
     * Descriptor read request status output
     */
    output wire [QUEUE_INDEX_WIDTH-1:0]           m_axis_req_status_queue,
    output wire [QUEUE_PTR_WIDTH-1:0]             m_axis_req_status_ptr,
    output wire [CPL_QUEUE_INDEX_WIDTH-1:0]       m_axis_req_status_cpl,
    output wire [REQ_TAG_WIDTH-1:0]               m_axis_req_status_tag,
    output wire                                   m_axis_req_status_empty,
    output wire                                   m_axis_req_status_error,
    output wire                                   m_axis_req_status_valid,

    /*
     * Descriptor data output
     */
    output wire [AXIS_DATA_WIDTH-1:0]             m_axis_desc_tdata,
    output wire [AXIS_KEEP_WIDTH-1:0]             m_axis_desc_tkeep,
    output wire                                   m_axis_desc_tvalid,
    input  wire                                   m_axis_desc_tready,
    output wire                                   m_axis_desc_tlast,
    output wire [REQ_TAG_WIDTH-1:0]               m_axis_desc_tid,
    output wire                                   m_axis_desc_tuser,

    /*
     * Descriptor dequeue request output
     */
    output wire [PORTS*QUEUE_INDEX_WIDTH-1:0]     m_axis_desc_dequeue_req_queue,
    output wire [PORTS*REQ_TAG_WIDTH-1:0]         m_axis_desc_dequeue_req_tag,
    output wire [PORTS-1:0]                       m_axis_desc_dequeue_req_valid,
    input  wire [PORTS-1:0]                       m_axis_desc_dequeue_req_ready,

    /*
     * Descriptor dequeue response input
     */
    input  wire [PORTS*QUEUE_INDEX_WIDTH-1:0]     s_axis_desc_dequeue_resp_queue,
    input  wire [PORTS*QUEUE_PTR_WIDTH-1:0]       s_axis_desc_dequeue_resp_ptr,
    input  wire [PORTS*DMA_ADDR_WIDTH-1:0]        s_axis_desc_dequeue_resp_addr,
    input  wire [PORTS*LOG_BLOCK_SIZE_WIDTH-1:0]  s_axis_desc_dequeue_resp_block_size,
    input  wire [PORTS*CPL_QUEUE_INDEX_WIDTH-1:0] s_axis_desc_dequeue_resp_cpl,
    input  wire [PORTS*QUEUE_REQ_TAG_WIDTH-1:0]   s_axis_desc_dequeue_resp_tag,
    input  wire [PORTS*QUEUE_OP_TAG_WIDTH-1:0]    s_axis_desc_dequeue_resp_op_tag,
    input  wire [PORTS-1:0]                       s_axis_desc_dequeue_resp_empty,
    input  wire [PORTS-1:0]                       s_axis_desc_dequeue_resp_error,
    input  wire [PORTS-1:0]                       s_axis_desc_dequeue_resp_valid,
    output wire [PORTS-1:0]                       s_axis_desc_dequeue_resp_ready,

    /*
     * Descriptor dequeue commit output
     */
    output wire [PORTS*QUEUE_OP_TAG_WIDTH-1:0]    m_axis_desc_dequeue_commit_op_tag,
    output wire [PORTS-1:0]                       m_axis_desc_dequeue_commit_valid,
    input  wire [PORTS-1:0]                       m_axis_desc_dequeue_commit_ready,

    /*
     * DMA read descriptor output
     */
    output wire [DMA_ADDR_WIDTH-1:0]              m_axis_dma_read_desc_dma_addr,
    output wire [RAM_ADDR_WIDTH-1:0]              m_axis_dma_read_desc_ram_addr,
    output wire [DMA_LEN_WIDTH-1:0]               m_axis_dma_read_desc_len,
    output wire [DMA_TAG_WIDTH-1:0]               m_axis_dma_read_desc_tag,
    output wire                                   m_axis_dma_read_desc_valid,
    input  wire                                   m_axis_dma_read_desc_ready,

    /*
     * DMA read descriptor status input
     */
    input  wire [DMA_TAG_WIDTH-1:0]               s_axis_dma_read_desc_status_tag,
    input  wire                                   s_axis_dma_read_desc_status_valid,

    /*
     * RAM interface
     */
    input  wire [SEG_COUNT*SEG_BE_WIDTH-1:0]      dma_ram_wr_cmd_be,
    input  wire [SEG_COUNT*SEG_ADDR_WIDTH-1:0]    dma_ram_wr_cmd_addr,
    input  wire [SEG_COUNT*SEG_DATA_WIDTH-1:0]    dma_ram_wr_cmd_data,
    input  wire [SEG_COUNT-1:0]                   dma_ram_wr_cmd_valid,
    output wire [SEG_COUNT-1:0]                   dma_ram_wr_cmd_ready,

    /*
     * Configuration
     */
    input  wire                                   enable
);

parameter CL_DESC_TABLE_SIZE = $clog2(DESC_TABLE_SIZE);
parameter DESC_PTR_MASK = {CL_DESC_TABLE_SIZE{1'b1}};

parameter CL_PORTS = $clog2(PORTS);

parameter CL_DESC_SIZE = $clog2(DESC_SIZE);

// bus width assertions
initial begin
    if (DMA_TAG_WIDTH < CL_DESC_TABLE_SIZE) begin
        $error("Error: DMA tag width insufficient for descriptor table size (instance %m)");
        $finish;
    end

    if (QUEUE_REQ_TAG_WIDTH < CL_DESC_TABLE_SIZE) begin
        $error("Error: Queue request tag width insufficient for descriptor table size (instance %m)");
        $finish;
    end

    if (QUEUE_REQ_TAG_WIDTH < REQ_TAG_WIDTH) begin
        $error("Error: QUEUE_REQ_TAG_WIDTH must be at least REQ_TAG_WIDTH (instance %m)");
        $finish;
    end

    if (AXIS_KEEP_WIDTH * 8 != AXIS_DATA_WIDTH) begin
        $error("Error: AXI stream interface requires byte (8-bit) granularity (instance %m)");
        $finish;
    end

    if (2**CL_DESC_SIZE != DESC_SIZE) begin
        $error("Error: Descriptor size must be even power of two (instance %m)");
        $finish;
    end
end

reg s_axis_req_ready_reg = 1'b0, s_axis_req_ready_next;

reg [QUEUE_INDEX_WIDTH-1:0] m_axis_req_status_queue_reg = {QUEUE_INDEX_WIDTH{1'b0}}, m_axis_req_status_queue_next;
reg [QUEUE_PTR_WIDTH-1:0] m_axis_req_status_ptr_reg = {QUEUE_PTR_WIDTH{1'b0}}, m_axis_req_status_ptr_next;
reg [CPL_QUEUE_INDEX_WIDTH-1:0] m_axis_req_status_cpl_reg = {CPL_QUEUE_INDEX_WIDTH{1'b0}}, m_axis_req_status_cpl_next;
reg [REQ_TAG_WIDTH-1:0] m_axis_req_status_tag_reg = {REQ_TAG_WIDTH{1'b0}}, m_axis_req_status_tag_next;
reg m_axis_req_status_empty_reg = 1'b0, m_axis_req_status_empty_next;
reg m_axis_req_status_error_reg = 1'b0, m_axis_req_status_error_next;
reg m_axis_req_status_valid_reg = 1'b0, m_axis_req_status_valid_next;

reg [QUEUE_INDEX_WIDTH-1:0] m_axis_desc_dequeue_req_queue_reg = {QUEUE_INDEX_WIDTH{1'b0}}, m_axis_desc_dequeue_req_queue_next;
reg [QUEUE_REQ_TAG_WIDTH-1:0] m_axis_desc_dequeue_req_tag_reg = {QUEUE_REQ_TAG_WIDTH{1'b0}}, m_axis_desc_dequeue_req_tag_next;
reg [PORTS-1:0] m_axis_desc_dequeue_req_valid_reg = {PORTS{1'b0}}, m_axis_desc_dequeue_req_valid_next;

reg [PORTS-1:0] s_axis_desc_dequeue_resp_ready_reg = {PORTS{1'b0}}, s_axis_desc_dequeue_resp_ready_next;

reg [QUEUE_OP_TAG_WIDTH-1:0] m_axis_desc_dequeue_commit_op_tag_reg = {QUEUE_OP_TAG_WIDTH{1'b0}}, m_axis_desc_dequeue_commit_op_tag_next;
reg [PORTS-1:0] m_axis_desc_dequeue_commit_valid_reg = {PORTS{1'b0}}, m_axis_desc_dequeue_commit_valid_next;

reg [DMA_ADDR_WIDTH-1:0] m_axis_dma_read_desc_dma_addr_reg = {DMA_ADDR_WIDTH{1'b0}}, m_axis_dma_read_desc_dma_addr_next;
reg [RAM_ADDR_WIDTH-1:0] m_axis_dma_read_desc_ram_addr_reg = {RAM_ADDR_WIDTH{1'b0}}, m_axis_dma_read_desc_ram_addr_next;
reg [DMA_LEN_WIDTH-1:0] m_axis_dma_read_desc_len_reg = {DMA_LEN_WIDTH{1'b0}}, m_axis_dma_read_desc_len_next;
reg [DMA_TAG_WIDTH-1:0] m_axis_dma_read_desc_tag_reg = {DMA_TAG_WIDTH{1'b0}}, m_axis_dma_read_desc_tag_next;
reg m_axis_dma_read_desc_valid_reg = 1'b0, m_axis_dma_read_desc_valid_next;

reg [CL_DESC_TABLE_SIZE+1-1:0] active_count_reg = 0;
reg inc_active;
reg dec_active_1;
reg dec_active_2;

reg [DESC_TABLE_SIZE-1:0] desc_table_active = 0;
reg [DESC_TABLE_SIZE-1:0] desc_table_desc_fetched = 0;
reg [DESC_TABLE_SIZE-1:0] desc_table_desc_read_done = 0;
reg [CL_PORTS-1:0] desc_table_sel[DESC_TABLE_SIZE-1:0];
reg [LOG_BLOCK_SIZE_WIDTH-1:0] desc_table_log_desc_block_size[DESC_TABLE_SIZE-1:0];
reg [REQ_TAG_WIDTH-1:0] desc_table_tag[DESC_TABLE_SIZE-1:0];
reg [QUEUE_OP_TAG_WIDTH-1:0] desc_table_queue_op_tag[DESC_TABLE_SIZE-1:0];

reg [CL_DESC_TABLE_SIZE+1-1:0] desc_table_start_ptr_reg = 0;
reg [CL_PORTS-1:0] desc_table_start_sel;
reg [LOG_BLOCK_SIZE_WIDTH-1:0] desc_table_start_log_desc_block_size;
reg [REQ_TAG_WIDTH-1:0] desc_table_start_tag;
reg [QUEUE_OP_TAG_WIDTH-1:0] desc_table_start_queue_op_tag;
reg desc_table_start_en;
reg [CL_DESC_TABLE_SIZE-1:0] desc_table_desc_fetched_ptr;
reg desc_table_desc_fetched_en;
reg [CL_DESC_TABLE_SIZE+1-1:0] desc_table_desc_read_ptr_reg = 0;
reg desc_table_desc_read_en;
reg [CL_DESC_TABLE_SIZE-1:0] desc_table_desc_read_done_ptr;
reg desc_table_desc_read_done_en;
reg [CL_DESC_TABLE_SIZE+1-1:0] desc_table_finish_ptr_reg = 0;
reg desc_table_finish_en;

reg [RAM_ADDR_WIDTH-1:0] dma_read_desc_ram_addr_reg = {RAM_ADDR_WIDTH{1'b0}}, dma_read_desc_ram_addr_next;
reg [7:0] dma_read_desc_len_reg = 8'd0, dma_read_desc_len_next;
reg [CL_DESC_TABLE_SIZE-1:0] dma_read_desc_tag_reg = {CL_DESC_TABLE_SIZE{1'b0}}, dma_read_desc_tag_next;
reg [REQ_TAG_WIDTH-1:0] dma_read_desc_id_reg = {REQ_TAG_WIDTH{1'b0}}, dma_read_desc_id_next;
reg dma_read_desc_user_reg = 1'b0, dma_read_desc_user_next;
reg dma_read_desc_valid_reg = 1'b0, dma_read_desc_valid_next;
wire dma_read_desc_ready;

wire [CL_DESC_TABLE_SIZE-1:0] dma_read_desc_status_tag;
wire dma_read_desc_status_valid;

assign s_axis_req_ready = s_axis_req_ready_reg;

assign m_axis_req_status_queue = m_axis_req_status_queue_reg;
assign m_axis_req_status_ptr = m_axis_req_status_ptr_reg;
assign m_axis_req_status_cpl = m_axis_req_status_cpl_reg;
assign m_axis_req_status_tag = m_axis_req_status_tag_reg;
assign m_axis_req_status_empty = m_axis_req_status_empty_reg;
assign m_axis_req_status_error = m_axis_req_status_error_reg;
assign m_axis_req_status_valid = m_axis_req_status_valid_reg;

assign m_axis_desc_dequeue_req_queue = {PORTS{m_axis_desc_dequeue_req_queue_reg}};
assign m_axis_desc_dequeue_req_tag = {PORTS{m_axis_desc_dequeue_req_tag_reg}};
assign m_axis_desc_dequeue_req_valid = m_axis_desc_dequeue_req_valid_reg;

assign s_axis_desc_dequeue_resp_ready = s_axis_desc_dequeue_resp_ready_reg;

assign m_axis_desc_dequeue_commit_op_tag = {PORTS{m_axis_desc_dequeue_commit_op_tag_reg}};
assign m_axis_desc_dequeue_commit_valid = m_axis_desc_dequeue_commit_valid_reg;

assign m_axis_dma_read_desc_dma_addr = m_axis_dma_read_desc_dma_addr_reg;
assign m_axis_dma_read_desc_ram_addr = m_axis_dma_read_desc_ram_addr_reg;
assign m_axis_dma_read_desc_len = m_axis_dma_read_desc_len_reg;
assign m_axis_dma_read_desc_tag = m_axis_dma_read_desc_tag_reg;
assign m_axis_dma_read_desc_valid = m_axis_dma_read_desc_valid_reg;

wire [CL_PORTS-1:0] dequeue_resp_enc;
wire dequeue_resp_enc_valid;

priority_encoder #(
    .WIDTH(PORTS),
    .LSB_PRIORITY("HIGH")
)
op_table_start_enc_inst (
    .input_unencoded(s_axis_desc_dequeue_resp_valid & ~s_axis_desc_dequeue_resp_ready),
    .output_valid(dequeue_resp_enc_valid),
    .output_encoded(dequeue_resp_enc),
    .output_unencoded()
);

wire [SEG_COUNT*SEG_ADDR_WIDTH-1:0]  dma_ram_rd_cmd_addr_int;
wire [SEG_COUNT-1:0]                 dma_ram_rd_cmd_valid_int;
wire [SEG_COUNT-1:0]                 dma_ram_rd_cmd_ready_int;
wire [SEG_COUNT*SEG_DATA_WIDTH-1:0]  dma_ram_rd_resp_data_int;
wire [SEG_COUNT-1:0]                 dma_ram_rd_resp_valid_int;
wire [SEG_COUNT-1:0]                 dma_ram_rd_resp_ready_int;

dma_psdpram #(
    .SIZE(DESC_TABLE_SIZE*DESC_SIZE*(2**((2**LOG_BLOCK_SIZE_WIDTH)-1))),
    .SEG_COUNT(SEG_COUNT),
    .SEG_DATA_WIDTH(SEG_DATA_WIDTH),
    .SEG_ADDR_WIDTH(SEG_ADDR_WIDTH),
    .SEG_BE_WIDTH(SEG_BE_WIDTH),
    .PIPELINE(RAM_PIPELINE)
)
dma_psdpram_inst (
    /*
     * Write port
     */
    .clk_wr(clk),
    .rst_wr(rst),
    .wr_cmd_be(dma_ram_wr_cmd_be),
    .wr_cmd_addr(dma_ram_wr_cmd_addr),
    .wr_cmd_data(dma_ram_wr_cmd_data),
    .wr_cmd_valid(dma_ram_wr_cmd_valid),
    .wr_cmd_ready(dma_ram_wr_cmd_ready),

    /*
     * Read port
     */
    .clk_rd(clk),
    .rst_rd(rst),
    .rd_cmd_addr(dma_ram_rd_cmd_addr_int),
    .rd_cmd_valid(dma_ram_rd_cmd_valid_int),
    .rd_cmd_ready(dma_ram_rd_cmd_ready_int),
    .rd_resp_data(dma_ram_rd_resp_data_int),
    .rd_resp_valid(dma_ram_rd_resp_valid_int),
    .rd_resp_ready(dma_ram_rd_resp_ready_int)
);

dma_client_axis_source #(
    .SEG_COUNT(SEG_COUNT),
    .SEG_DATA_WIDTH(SEG_DATA_WIDTH),
    .SEG_ADDR_WIDTH(SEG_ADDR_WIDTH),
    .SEG_BE_WIDTH(SEG_BE_WIDTH),
    .RAM_ADDR_WIDTH(RAM_ADDR_WIDTH),
    .AXIS_DATA_WIDTH(AXIS_DATA_WIDTH),
    .AXIS_KEEP_ENABLE(AXIS_KEEP_WIDTH > 1),
    .AXIS_KEEP_WIDTH(AXIS_KEEP_WIDTH),
    .AXIS_LAST_ENABLE(1),
    .AXIS_ID_ENABLE(1),
    .AXIS_ID_WIDTH(REQ_TAG_WIDTH),
    .AXIS_DEST_ENABLE(0),
    .AXIS_USER_ENABLE(1),
    .AXIS_USER_WIDTH(1),
    .LEN_WIDTH(8),
    .TAG_WIDTH(CL_DESC_TABLE_SIZE)
)
dma_client_axis_source_inst (
    .clk(clk),
    .rst(rst),

    /*
     * DMA read descriptor input
     */
    .s_axis_read_desc_ram_addr(dma_read_desc_ram_addr_reg),
    .s_axis_read_desc_len(dma_read_desc_len_reg),
    .s_axis_read_desc_tag(dma_read_desc_tag_reg),
    .s_axis_read_desc_id(dma_read_desc_id_reg),
    .s_axis_read_desc_dest(0),
    .s_axis_read_desc_user(dma_read_desc_user_reg),
    .s_axis_read_desc_valid(dma_read_desc_valid_reg),
    .s_axis_read_desc_ready(dma_read_desc_ready),

    /*
     * DMA read descriptor status output
     */
    .m_axis_read_desc_status_tag(dma_read_desc_status_tag),
    .m_axis_read_desc_status_valid(dma_read_desc_status_valid),

    /*
     * AXI stream read data output
     */
    .m_axis_read_data_tdata(m_axis_desc_tdata),
    .m_axis_read_data_tkeep(m_axis_desc_tkeep),
    .m_axis_read_data_tvalid(m_axis_desc_tvalid),
    .m_axis_read_data_tready(m_axis_desc_tready),
    .m_axis_read_data_tlast(m_axis_desc_tlast),
    .m_axis_read_data_tid(m_axis_desc_tid),
    .m_axis_read_data_tdest(),
    .m_axis_read_data_tuser(m_axis_desc_tuser),

    /*
     * RAM interface
     */
    .ram_rd_cmd_addr(dma_ram_rd_cmd_addr_int),
    .ram_rd_cmd_valid(dma_ram_rd_cmd_valid_int),
    .ram_rd_cmd_ready(dma_ram_rd_cmd_ready_int),
    .ram_rd_resp_data(dma_ram_rd_resp_data_int),
    .ram_rd_resp_valid(dma_ram_rd_resp_valid_int),
    .ram_rd_resp_ready(dma_ram_rd_resp_ready_int),

    /*
     * Configuration
     */
    .enable(1'b1)
);

always @* begin
    s_axis_req_ready_next = 1'b0;

    m_axis_req_status_queue_next = m_axis_req_status_queue_reg;
    m_axis_req_status_ptr_next = m_axis_req_status_ptr_reg;
    m_axis_req_status_cpl_next = m_axis_req_status_cpl_reg;
    m_axis_req_status_tag_next = m_axis_req_status_tag_reg;
    m_axis_req_status_empty_next = m_axis_req_status_empty_reg;
    m_axis_req_status_error_next = m_axis_req_status_error_reg;
    m_axis_req_status_valid_next = 1'b0;

    m_axis_desc_dequeue_req_queue_next = m_axis_desc_dequeue_req_queue_reg;
    m_axis_desc_dequeue_req_tag_next = m_axis_desc_dequeue_req_tag_reg;
    m_axis_desc_dequeue_req_valid_next = m_axis_desc_dequeue_req_valid_reg & ~m_axis_desc_dequeue_req_ready;

    s_axis_desc_dequeue_resp_ready_next = {PORTS{1'b0}};

    m_axis_desc_dequeue_commit_op_tag_next = m_axis_desc_dequeue_commit_op_tag_reg;
    m_axis_desc_dequeue_commit_valid_next = m_axis_desc_dequeue_commit_valid_reg & ~m_axis_desc_dequeue_commit_ready;

    m_axis_dma_read_desc_dma_addr_next = m_axis_dma_read_desc_dma_addr_reg;
    m_axis_dma_read_desc_ram_addr_next = m_axis_dma_read_desc_ram_addr_reg;
    m_axis_dma_read_desc_len_next = m_axis_dma_read_desc_len_reg;
    m_axis_dma_read_desc_tag_next = m_axis_dma_read_desc_tag_reg;
    m_axis_dma_read_desc_valid_next = m_axis_dma_read_desc_valid_reg && !m_axis_dma_read_desc_ready;

    dma_read_desc_ram_addr_next = dma_read_desc_ram_addr_reg;
    dma_read_desc_len_next = dma_read_desc_len_reg;
    dma_read_desc_tag_next = dma_read_desc_tag_reg;
    dma_read_desc_id_next = dma_read_desc_id_reg;
    dma_read_desc_user_next = dma_read_desc_user_reg;
    dma_read_desc_valid_next = dma_read_desc_valid_reg && !dma_read_desc_ready;

    inc_active = 1'b0;
    dec_active_1 = 1'b0;
    dec_active_2 = 1'b0;

    desc_table_start_sel = dequeue_resp_enc;
    desc_table_start_log_desc_block_size = s_axis_desc_dequeue_resp_block_size[dequeue_resp_enc*LOG_BLOCK_SIZE_WIDTH +: LOG_BLOCK_SIZE_WIDTH];
    desc_table_start_tag = s_axis_desc_dequeue_resp_tag[dequeue_resp_enc*QUEUE_REQ_TAG_WIDTH +: QUEUE_REQ_TAG_WIDTH];
    desc_table_start_queue_op_tag = s_axis_desc_dequeue_resp_op_tag[dequeue_resp_enc*QUEUE_OP_TAG_WIDTH +: QUEUE_OP_TAG_WIDTH];
    desc_table_start_en = 1'b0;
    desc_table_desc_fetched_ptr = s_axis_dma_read_desc_status_tag & DESC_PTR_MASK;
    desc_table_desc_fetched_en = 1'b0;
    desc_table_desc_read_en = 1'b0;
    desc_table_desc_read_done_ptr = dma_read_desc_status_tag & DESC_PTR_MASK;
    desc_table_desc_read_done_en = 1'b0;
    desc_table_finish_en = 1'b0;

    // queue query
    // wait for descriptor request
    s_axis_req_ready_next = enable && active_count_reg < DESC_TABLE_SIZE && !desc_table_active[desc_table_start_ptr_reg & DESC_PTR_MASK] && ($unsigned(desc_table_start_ptr_reg - desc_table_finish_ptr_reg) < DESC_TABLE_SIZE) && (!m_axis_desc_dequeue_req_valid_reg || (m_axis_desc_dequeue_req_valid_reg & m_axis_desc_dequeue_req_ready));
    if (s_axis_req_ready && s_axis_req_valid) begin
        s_axis_req_ready_next = 1'b0;

        // initiate queue query
        m_axis_desc_dequeue_req_queue_next = s_axis_req_queue;
        m_axis_desc_dequeue_req_tag_next = s_axis_req_tag;
        m_axis_desc_dequeue_req_valid_next = 1 << s_axis_req_sel;

        inc_active = 1'b1;
    end

    // descriptor fetch
    // wait for queue query response
    if (dequeue_resp_enc_valid && !m_axis_dma_read_desc_valid_reg && !desc_table_active[desc_table_start_ptr_reg & DESC_PTR_MASK] && ($unsigned(desc_table_start_ptr_reg - desc_table_finish_ptr_reg) < DESC_TABLE_SIZE)) begin
        s_axis_desc_dequeue_resp_ready_next = 1 << dequeue_resp_enc;

        // store in descriptor table
        desc_table_start_sel = dequeue_resp_enc;
        desc_table_start_log_desc_block_size = s_axis_desc_dequeue_resp_block_size[dequeue_resp_enc*LOG_BLOCK_SIZE_WIDTH +: LOG_BLOCK_SIZE_WIDTH];
        desc_table_start_tag = s_axis_desc_dequeue_resp_tag[dequeue_resp_enc*QUEUE_REQ_TAG_WIDTH +: QUEUE_REQ_TAG_WIDTH];
        desc_table_start_queue_op_tag = s_axis_desc_dequeue_resp_op_tag[dequeue_resp_enc*QUEUE_OP_TAG_WIDTH +: QUEUE_OP_TAG_WIDTH];

        // return descriptor request completion
        m_axis_req_status_queue_next = s_axis_desc_dequeue_resp_queue[dequeue_resp_enc*QUEUE_INDEX_WIDTH +: QUEUE_INDEX_WIDTH];
        m_axis_req_status_ptr_next = s_axis_desc_dequeue_resp_ptr[dequeue_resp_enc*QUEUE_PTR_WIDTH +: QUEUE_PTR_WIDTH];
        m_axis_req_status_cpl_next = s_axis_desc_dequeue_resp_cpl[dequeue_resp_enc*CPL_QUEUE_INDEX_WIDTH +: CPL_QUEUE_INDEX_WIDTH];
        m_axis_req_status_tag_next = s_axis_desc_dequeue_resp_tag[dequeue_resp_enc*QUEUE_REQ_TAG_WIDTH +: QUEUE_REQ_TAG_WIDTH];
        m_axis_req_status_empty_next = s_axis_desc_dequeue_resp_empty[dequeue_resp_enc*1 +: 1];
        m_axis_req_status_error_next = s_axis_desc_dequeue_resp_error[dequeue_resp_enc*1 +: 1];
        m_axis_req_status_valid_next = 1'b1;

        // initiate descriptor fetch
        m_axis_dma_read_desc_dma_addr_next = s_axis_desc_dequeue_resp_addr[dequeue_resp_enc*DMA_ADDR_WIDTH +: DMA_ADDR_WIDTH];
        m_axis_dma_read_desc_ram_addr_next = (desc_table_start_ptr_reg & DESC_PTR_MASK) << (CL_DESC_SIZE+(2**LOG_BLOCK_SIZE_WIDTH)-1);
        m_axis_dma_read_desc_len_next = DESC_SIZE << s_axis_desc_dequeue_resp_block_size[dequeue_resp_enc*LOG_BLOCK_SIZE_WIDTH +: LOG_BLOCK_SIZE_WIDTH];
        m_axis_dma_read_desc_tag_next = (desc_table_start_ptr_reg & DESC_PTR_MASK);

        if (s_axis_desc_dequeue_resp_error[dequeue_resp_enc*1 +: 1] || s_axis_desc_dequeue_resp_empty[dequeue_resp_enc*1 +: 1]) begin
            // queue empty or not active

            dec_active_1 = 1'b1;
        end else begin
            // descriptor available to dequeue

            // store in descriptor table
            desc_table_start_en = 1'b1;

            // initiate descriptor fetch
            m_axis_dma_read_desc_valid_next = 1'b1;
        end
    end

    // descriptor fetch completion
    // wait for descriptor fetch completion
    if (s_axis_dma_read_desc_status_valid) begin
        // update entry in descriptor table
        desc_table_desc_fetched_ptr = s_axis_dma_read_desc_status_tag & DESC_PTR_MASK;
        desc_table_desc_fetched_en = 1'b1;
    end

    // return descriptor
    // wait for descriptor fetch completion
    // TODO descriptor validation?
    if (desc_table_active[desc_table_desc_read_ptr_reg & DESC_PTR_MASK] && desc_table_desc_read_ptr_reg != desc_table_start_ptr_reg) begin
        if (desc_table_desc_fetched[desc_table_desc_read_ptr_reg & DESC_PTR_MASK] && !(m_axis_desc_dequeue_commit_valid & 1 << desc_table_sel[desc_table_desc_read_ptr_reg & DESC_PTR_MASK]) && !dma_read_desc_valid_reg) begin
            // update entry in descriptor table
            desc_table_desc_read_en = 1'b1;

            // commit dequeue operation
            m_axis_desc_dequeue_commit_op_tag_next = desc_table_queue_op_tag[desc_table_desc_read_ptr_reg & DESC_PTR_MASK];
            m_axis_desc_dequeue_commit_valid_next = 1 << desc_table_sel[desc_table_desc_read_ptr_reg & DESC_PTR_MASK];

            // initiate descriptor read from DMA RAM
            dma_read_desc_ram_addr_next = (desc_table_desc_read_ptr_reg & DESC_PTR_MASK) << (CL_DESC_SIZE+(2**LOG_BLOCK_SIZE_WIDTH)-1);
            dma_read_desc_len_next = DESC_SIZE << desc_table_log_desc_block_size[desc_table_desc_read_ptr_reg & DESC_PTR_MASK];
            dma_read_desc_tag_next = (desc_table_desc_read_ptr_reg & DESC_PTR_MASK);
            dma_read_desc_id_next = desc_table_tag[desc_table_desc_read_ptr_reg & DESC_PTR_MASK];
            dma_read_desc_user_next = 1'b0;
            dma_read_desc_valid_next = 1'b1;
        end
    end

    // descriptor read completion
    // wait for descriptor read completion
    if (dma_read_desc_status_valid) begin
        // update entry in descriptor table
        desc_table_desc_read_done_ptr = dma_read_desc_status_tag & DESC_PTR_MASK;
        desc_table_desc_read_done_en = 1'b1;
    end

    // finish operation
    // wait for descriptor read completion
    if (desc_table_active[desc_table_finish_ptr_reg & DESC_PTR_MASK] && desc_table_finish_ptr_reg != desc_table_start_ptr_reg) begin
        if (desc_table_desc_read_done[desc_table_finish_ptr_reg & DESC_PTR_MASK]) begin
            // invalidate entry in descriptor table
            desc_table_finish_en = 1'b1;

            dec_active_2 = 1'b1;
        end
    end
end

always @(posedge clk) begin
    s_axis_req_ready_reg <= s_axis_req_ready_next;

    m_axis_req_status_queue_reg <= m_axis_req_status_queue_next;
    m_axis_req_status_ptr_reg <= m_axis_req_status_ptr_next;
    m_axis_req_status_cpl_reg <= m_axis_req_status_cpl_next;
    m_axis_req_status_tag_reg <= m_axis_req_status_tag_next;
    m_axis_req_status_empty_reg <= m_axis_req_status_empty_next;
    m_axis_req_status_error_reg <= m_axis_req_status_error_next;
    m_axis_req_status_valid_reg <= m_axis_req_status_valid_next;

    m_axis_desc_dequeue_req_queue_reg <= m_axis_desc_dequeue_req_queue_next;
    m_axis_desc_dequeue_req_tag_reg <= m_axis_desc_dequeue_req_tag_next;
    m_axis_desc_dequeue_req_valid_reg <= m_axis_desc_dequeue_req_valid_next;

    s_axis_desc_dequeue_resp_ready_reg <= s_axis_desc_dequeue_resp_ready_next;

    m_axis_desc_dequeue_commit_op_tag_reg <= m_axis_desc_dequeue_commit_op_tag_next;
    m_axis_desc_dequeue_commit_valid_reg <= m_axis_desc_dequeue_commit_valid_next;

    m_axis_dma_read_desc_dma_addr_reg <= m_axis_dma_read_desc_dma_addr_next;
    m_axis_dma_read_desc_ram_addr_reg <= m_axis_dma_read_desc_ram_addr_next;
    m_axis_dma_read_desc_len_reg <= m_axis_dma_read_desc_len_next;
    m_axis_dma_read_desc_tag_reg <= m_axis_dma_read_desc_tag_next;
    m_axis_dma_read_desc_valid_reg <= m_axis_dma_read_desc_valid_next;

    dma_read_desc_ram_addr_reg <= dma_read_desc_ram_addr_next;
    dma_read_desc_len_reg <= dma_read_desc_len_next;
    dma_read_desc_tag_reg <= dma_read_desc_tag_next;
    dma_read_desc_id_reg <= dma_read_desc_id_next;
    dma_read_desc_user_reg <= dma_read_desc_user_next;
    dma_read_desc_valid_reg <= dma_read_desc_valid_next;

    active_count_reg <= active_count_reg + inc_active - dec_active_1 - dec_active_2;

    if (desc_table_start_en) begin
        desc_table_active[desc_table_start_ptr_reg & DESC_PTR_MASK] <= 1'b1;
        desc_table_desc_fetched[desc_table_start_ptr_reg & DESC_PTR_MASK] <= 1'b0;
        desc_table_desc_read_done[desc_table_start_ptr_reg & DESC_PTR_MASK] <= 1'b0;
        desc_table_sel[desc_table_start_ptr_reg & DESC_PTR_MASK] <= desc_table_start_sel;
        desc_table_log_desc_block_size[desc_table_start_ptr_reg & DESC_PTR_MASK] <= desc_table_start_log_desc_block_size;
        desc_table_tag[desc_table_start_ptr_reg & DESC_PTR_MASK] <= desc_table_start_tag;
        desc_table_queue_op_tag[desc_table_start_ptr_reg & DESC_PTR_MASK] <= desc_table_start_queue_op_tag;
        desc_table_start_ptr_reg <= desc_table_start_ptr_reg + 1;
    end

    if (desc_table_desc_fetched_en) begin
        desc_table_desc_fetched[desc_table_desc_fetched_ptr & DESC_PTR_MASK] <= 1'b1;
    end

    if (desc_table_desc_read_en) begin
        desc_table_desc_read_ptr_reg <= desc_table_desc_read_ptr_reg + 1;
    end

    if (desc_table_desc_read_done_en) begin
        desc_table_desc_read_done[desc_table_desc_read_done_ptr & DESC_PTR_MASK] <= 1'b1;
    end

    if (desc_table_finish_en) begin
        desc_table_active[desc_table_finish_ptr_reg & DESC_PTR_MASK] <= 1'b0;
        desc_table_finish_ptr_reg <= desc_table_finish_ptr_reg + 1;
    end

    if (rst) begin
        s_axis_req_ready_reg <= 1'b0;
        m_axis_req_status_valid_reg <= 1'b0;
        m_axis_desc_dequeue_req_valid_reg <= {PORTS{1'b0}};
        s_axis_desc_dequeue_resp_ready_reg <= {PORTS{1'b0}};
        m_axis_desc_dequeue_commit_valid_reg <= {PORTS{1'b0}};
        m_axis_dma_read_desc_valid_reg <= 1'b0;

        dma_read_desc_valid_reg <= 1'b0;

        active_count_reg <= 0;

        desc_table_active <= 0;
        desc_table_desc_fetched <= 0;

        desc_table_start_ptr_reg <= 0;
        desc_table_desc_read_ptr_reg <= 0;
        desc_table_finish_ptr_reg <= 0;
    end
end

endmodule