module axi_adapter_rd #
(
    // Width of address bus in bits
    parameter ADDR_WIDTH = 32,
    // Width of input (slave) interface data bus in bits
    parameter S_DATA_WIDTH = 32,
    // Width of input (slave) interface wstrb (width of data bus in words)
    parameter S_STRB_WIDTH = (S_DATA_WIDTH/8),
    // Width of output (master) interface data bus in bits
    parameter M_DATA_WIDTH = 32,
    // Width of output (master) interface wstrb (width of data bus in words)
    parameter M_STRB_WIDTH = (M_DATA_WIDTH/8),
    // Width of ID signal
    parameter ID_WIDTH = 8,
    // Propagate aruser signal
    parameter ARUSER_ENABLE = 0,
    // Width of aruser signal
    parameter ARUSER_WIDTH = 1,
    // Propagate ruser signal
    parameter RUSER_ENABLE = 0,
    // Width of ruser signal
    parameter RUSER_WIDTH = 1,
    // When adapting to a wider bus, re-pack full-width burst instead of passing through narrow burst if possible
    parameter CONVERT_BURST = 1,
    // When adapting to a wider bus, re-pack all bursts instead of passing through narrow burst if possible
    parameter CONVERT_NARROW_BURST = 0,
    // Forward ID through adapter
    parameter FORWARD_ID = 0
)
(
    input  wire                     clk,
    input  wire                     rst,

    /*
     * AXI slave interface
     */
    input  wire [ID_WIDTH-1:0]      s_axi_arid,
    input  wire [ADDR_WIDTH-1:0]    s_axi_araddr,
    input  wire [7:0]               s_axi_arlen,
    input  wire [2:0]               s_axi_arsize,
    input  wire [1:0]               s_axi_arburst,
    input  wire                     s_axi_arlock,
    input  wire [3:0]               s_axi_arcache,
    input  wire [2:0]               s_axi_arprot,
    input  wire [3:0]               s_axi_arqos,
    input  wire [3:0]               s_axi_arregion,
    input  wire [ARUSER_WIDTH-1:0]  s_axi_aruser,
    input  wire                     s_axi_arvalid,
    output wire                     s_axi_arready,
    output wire [ID_WIDTH-1:0]      s_axi_rid,
    output wire [S_DATA_WIDTH-1:0]  s_axi_rdata,
    output wire [1:0]               s_axi_rresp,
    output wire                     s_axi_rlast,
    output wire [RUSER_WIDTH-1:0]   s_axi_ruser,
    output wire                     s_axi_rvalid,
    input  wire                     s_axi_rready,

    /*
     * AXI master interface
     */
    output wire [ID_WIDTH-1:0]      m_axi_arid,
    output wire [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 [3:0]               m_axi_arqos,
    output wire [3:0]               m_axi_arregion,
    output wire [ARUSER_WIDTH-1:0]  m_axi_aruser,
    output wire                     m_axi_arvalid,
    input  wire                     m_axi_arready,
    input  wire [ID_WIDTH-1:0]      m_axi_rid,
    input  wire [M_DATA_WIDTH-1:0]  m_axi_rdata,
    input  wire [1:0]               m_axi_rresp,
    input  wire                     m_axi_rlast,
    input  wire [RUSER_WIDTH-1:0]   m_axi_ruser,
    input  wire                     m_axi_rvalid,
    output wire                     m_axi_rready
);

parameter S_ADDR_BIT_OFFSET = $clog2(S_STRB_WIDTH);
parameter M_ADDR_BIT_OFFSET = $clog2(M_STRB_WIDTH);
parameter S_WORD_WIDTH = S_STRB_WIDTH;
parameter M_WORD_WIDTH = M_STRB_WIDTH;
parameter S_WORD_SIZE = S_DATA_WIDTH/S_WORD_WIDTH;
parameter M_WORD_SIZE = M_DATA_WIDTH/M_WORD_WIDTH;
parameter S_BURST_SIZE = $clog2(S_STRB_WIDTH);
parameter M_BURST_SIZE = $clog2(M_STRB_WIDTH);

// output bus is wider
parameter EXPAND = M_STRB_WIDTH > S_STRB_WIDTH;
parameter DATA_WIDTH = EXPAND ? M_DATA_WIDTH : S_DATA_WIDTH;
parameter STRB_WIDTH = EXPAND ? M_STRB_WIDTH : S_STRB_WIDTH;
// required number of segments in wider bus
parameter SEGMENT_COUNT = EXPAND ? (M_STRB_WIDTH / S_STRB_WIDTH) : (S_STRB_WIDTH / M_STRB_WIDTH);
// data width and keep width per segment
parameter SEGMENT_DATA_WIDTH = DATA_WIDTH / SEGMENT_COUNT;
parameter SEGMENT_STRB_WIDTH = STRB_WIDTH / SEGMENT_COUNT;

// bus width assertions
initial begin
    if (S_WORD_SIZE * S_STRB_WIDTH != S_DATA_WIDTH) begin
        $error("Error: AXI slave interface data width not evenly divisble (instance %m)");
        $finish;
    end

    if (M_WORD_SIZE * M_STRB_WIDTH != M_DATA_WIDTH) begin
        $error("Error: AXI master interface data width not evenly divisble (instance %m)");
        $finish;
    end

    if (S_WORD_SIZE != M_WORD_SIZE) begin
        $error("Error: word size mismatch (instance %m)");
        $finish;
    end

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

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

localparam [1:0]
    STATE_IDLE = 2'd0,
    STATE_DATA = 2'd1,
    STATE_DATA_READ = 2'd2,
    STATE_DATA_SPLIT = 2'd3;

reg [1:0] state_reg = STATE_IDLE, state_next;

reg [ID_WIDTH-1:0] id_reg = {ID_WIDTH{1'b0}}, id_next;
reg [ADDR_WIDTH-1:0] addr_reg = {ADDR_WIDTH{1'b0}}, addr_next;
reg [DATA_WIDTH-1:0] data_reg = {DATA_WIDTH{1'b0}}, data_next;
reg [1:0] resp_reg = 2'd0, resp_next;
reg [RUSER_WIDTH-1:0] ruser_reg = {RUSER_WIDTH{1'b0}}, ruser_next;
reg [7:0] burst_reg = 8'd0, burst_next;
reg [2:0] burst_size_reg = 3'd0, burst_size_next;
reg [7:0] master_burst_reg = 8'd0, master_burst_next;
reg [2:0] master_burst_size_reg = 3'd0, master_burst_size_next;

reg s_axi_arready_reg = 1'b0, s_axi_arready_next;

reg [ID_WIDTH-1:0] m_axi_arid_reg = {ID_WIDTH{1'b0}}, m_axi_arid_next;
reg [ADDR_WIDTH-1:0] m_axi_araddr_reg = {ADDR_WIDTH{1'b0}}, m_axi_araddr_next;
reg [7:0] m_axi_arlen_reg = 8'd0, m_axi_arlen_next;
reg [2:0] m_axi_arsize_reg = 3'd0, m_axi_arsize_next;
reg [1:0] m_axi_arburst_reg = 2'd0, m_axi_arburst_next;
reg m_axi_arlock_reg = 1'b0, m_axi_arlock_next;
reg [3:0] m_axi_arcache_reg = 4'd0, m_axi_arcache_next;
reg [2:0] m_axi_arprot_reg = 3'd0, m_axi_arprot_next;
reg [3:0] m_axi_arqos_reg = 4'd0, m_axi_arqos_next;
reg [3:0] m_axi_arregion_reg = 4'd0, m_axi_arregion_next;
reg [ARUSER_WIDTH-1:0] m_axi_aruser_reg = {ARUSER_WIDTH{1'b0}}, m_axi_aruser_next;
reg m_axi_arvalid_reg = 1'b0, m_axi_arvalid_next;
reg m_axi_rready_reg = 1'b0, m_axi_rready_next;

// internal datapath
reg  [ID_WIDTH-1:0]     s_axi_rid_int;
reg  [S_DATA_WIDTH-1:0] s_axi_rdata_int;
reg  [1:0]              s_axi_rresp_int;
reg                     s_axi_rlast_int;
reg  [RUSER_WIDTH-1:0]  s_axi_ruser_int;
reg                     s_axi_rvalid_int;
reg                     s_axi_rready_int_reg = 1'b0;
wire                    s_axi_rready_int_early;

assign s_axi_arready = s_axi_arready_reg;

assign m_axi_arid = FORWARD_ID ? m_axi_arid_reg : {ID_WIDTH{1'b0}};
assign m_axi_araddr = m_axi_araddr_reg;
assign m_axi_arlen = m_axi_arlen_reg;
assign m_axi_arsize = m_axi_arsize_reg;
assign m_axi_arburst = m_axi_arburst_reg;
assign m_axi_arlock = m_axi_arlock_reg;
assign m_axi_arcache = m_axi_arcache_reg;
assign m_axi_arprot = m_axi_arprot_reg;
assign m_axi_arqos = m_axi_arqos_reg;
assign m_axi_arregion = m_axi_arregion_reg;
assign m_axi_aruser = ARUSER_ENABLE ? m_axi_aruser_reg : {ARUSER_WIDTH{1'b0}};
assign m_axi_arvalid = m_axi_arvalid_reg;
assign m_axi_rready = m_axi_rready_reg;

always @* begin
    state_next = STATE_IDLE;

    id_next = id_reg;
    addr_next = addr_reg;
    data_next = data_reg;
    resp_next = resp_reg;
    ruser_next = ruser_reg;
    burst_next = burst_reg;
    burst_size_next = burst_size_reg;
    master_burst_next = master_burst_reg;
    master_burst_size_next = master_burst_size_reg;

    s_axi_arready_next = 1'b0;
    m_axi_arid_next = m_axi_arid_reg;
    m_axi_araddr_next = m_axi_araddr_reg;
    m_axi_arlen_next = m_axi_arlen_reg;
    m_axi_arsize_next = m_axi_arsize_reg;
    m_axi_arburst_next = m_axi_arburst_reg;
    m_axi_arlock_next = m_axi_arlock_reg;
    m_axi_arcache_next = m_axi_arcache_reg;
    m_axi_arprot_next = m_axi_arprot_reg;
    m_axi_arqos_next = m_axi_arqos_reg;
    m_axi_arregion_next = m_axi_arregion_reg;
    m_axi_aruser_next = m_axi_aruser_reg;
    m_axi_arvalid_next = m_axi_arvalid_reg && !m_axi_arready;
    m_axi_rready_next = 1'b0;

    if (SEGMENT_COUNT == 1) begin
        // master output is same width; direct transfer with no splitting/merging
        s_axi_rid_int = id_reg;
        s_axi_rdata_int = m_axi_rdata;
        s_axi_rresp_int = m_axi_rresp;
        s_axi_rlast_int = m_axi_rlast;
        s_axi_ruser_int = m_axi_ruser;
        s_axi_rvalid_int = 0;

        case (state_reg)
            STATE_IDLE: begin
                // idle state; wait for new burst
                s_axi_arready_next = !m_axi_arvalid;

                if (s_axi_arready && s_axi_arvalid) begin
                    s_axi_arready_next = 1'b0;
                    id_next = s_axi_arid;
                    m_axi_arid_next = s_axi_arid;
                    m_axi_araddr_next = s_axi_araddr;
                    m_axi_arlen_next = s_axi_arlen;
                    m_axi_arsize_next = s_axi_arsize;
                    m_axi_arburst_next = s_axi_arburst;
                    m_axi_arlock_next = s_axi_arlock;
                    m_axi_arcache_next = s_axi_arcache;
                    m_axi_arprot_next = s_axi_arprot;
                    m_axi_arqos_next = s_axi_arqos;
                    m_axi_arregion_next = s_axi_arregion;
                    m_axi_aruser_next = s_axi_aruser;
                    m_axi_arvalid_next = 1'b1;
                    m_axi_rready_next = s_axi_rready_int_early;
                    state_next = STATE_DATA;
                end else begin
                    state_next = STATE_IDLE;
                end
            end
            STATE_DATA: begin
                // data state; transfer read data
                m_axi_rready_next = s_axi_rready_int_early;

                if (m_axi_rready && m_axi_rvalid) begin
                    s_axi_rid_int = id_reg;
                    s_axi_rdata_int = m_axi_rdata;
                    s_axi_rresp_int = m_axi_rresp;
                    s_axi_rlast_int = m_axi_rlast;
                    s_axi_ruser_int = m_axi_ruser;
                    s_axi_rvalid_int = 1'b1;
                    if (m_axi_rlast) begin
                        // last data word, return to idle
                        m_axi_rready_next = 1'b0;
                        s_axi_arready_next = !m_axi_arvalid;
                        state_next = STATE_IDLE;
                    end else begin
                        state_next = STATE_DATA;
                    end
                end else begin
                    state_next = STATE_DATA;
                end
            end
        endcase
    end else if (EXPAND) begin
        // master output is wider; split reads
        s_axi_rid_int = id_reg;
        s_axi_rdata_int = m_axi_rdata;
        s_axi_rresp_int = m_axi_rresp;
        s_axi_rlast_int = m_axi_rlast;
        s_axi_ruser_int = m_axi_ruser;
        s_axi_rvalid_int = 0;

        case (state_reg)
            STATE_IDLE: begin
                // idle state; wait for new burst
                s_axi_arready_next = !m_axi_arvalid;

                if (s_axi_arready && s_axi_arvalid) begin
                    s_axi_arready_next = 1'b0;
                    id_next = s_axi_arid;
                    m_axi_arid_next = s_axi_arid;
                    m_axi_araddr_next = s_axi_araddr;
                    addr_next = s_axi_araddr;
                    burst_next = s_axi_arlen;
                    burst_size_next = s_axi_arsize;
                    if (CONVERT_BURST && s_axi_arcache[1] && (CONVERT_NARROW_BURST || s_axi_arsize == S_BURST_SIZE)) begin
                        // split reads
                        // require CONVERT_BURST and arcache[1] set
                        master_burst_size_next = M_BURST_SIZE;
                        if (CONVERT_NARROW_BURST) begin
                            m_axi_arlen_next = (({{S_ADDR_BIT_OFFSET+1{1'b0}}, s_axi_arlen} << s_axi_arsize) + s_axi_araddr[M_ADDR_BIT_OFFSET-1:0]) >> M_BURST_SIZE;
                        end else begin
                            m_axi_arlen_next = ({1'b0, s_axi_arlen} + s_axi_araddr[M_ADDR_BIT_OFFSET-1:S_ADDR_BIT_OFFSET]) >> $clog2(SEGMENT_COUNT);
                        end
                        m_axi_arsize_next = M_BURST_SIZE;
                        state_next = STATE_DATA_READ;
                    end else begin
                        // output narrow burst
                        master_burst_size_next = s_axi_arsize;
                        m_axi_arlen_next = s_axi_arlen;
                        m_axi_arsize_next = s_axi_arsize;
                        state_next = STATE_DATA;
                    end
                    m_axi_arburst_next = s_axi_arburst;
                    m_axi_arlock_next = s_axi_arlock;
                    m_axi_arcache_next = s_axi_arcache;
                    m_axi_arprot_next = s_axi_arprot;
                    m_axi_arqos_next = s_axi_arqos;
                    m_axi_arregion_next = s_axi_arregion;
                    m_axi_aruser_next = s_axi_aruser;
                    m_axi_arvalid_next = 1'b1;
                    m_axi_rready_next = s_axi_rready_int_early;
                end else begin
                    state_next = STATE_IDLE;
                end
            end
            STATE_DATA: begin
                m_axi_rready_next = s_axi_rready_int_early;

                if (m_axi_rready && m_axi_rvalid) begin
                    s_axi_rid_int = id_reg;
                    s_axi_rdata_int = m_axi_rdata >> (addr_reg[M_ADDR_BIT_OFFSET-1:S_ADDR_BIT_OFFSET] * S_DATA_WIDTH);
                    s_axi_rresp_int = m_axi_rresp;
                    s_axi_rlast_int = m_axi_rlast;
                    s_axi_ruser_int = m_axi_ruser;
                    s_axi_rvalid_int = 1'b1;
                    addr_next = addr_reg + (1 << burst_size_reg);
                    if (m_axi_rlast) begin
                        m_axi_rready_next = 1'b0;
                        s_axi_arready_next = !m_axi_arvalid;
                        state_next = STATE_IDLE;
                    end else begin
                        state_next = STATE_DATA;
                    end
                end else begin
                    state_next = STATE_DATA;
                end
            end
            STATE_DATA_READ: begin
                m_axi_rready_next = s_axi_rready_int_early;

                if (m_axi_rready && m_axi_rvalid) begin
                    s_axi_rid_int = id_reg;
                    data_next = m_axi_rdata;
                    resp_next = m_axi_rresp;
                    ruser_next = m_axi_ruser;
                    s_axi_rdata_int = m_axi_rdata >> (addr_reg[M_ADDR_BIT_OFFSET-1:S_ADDR_BIT_OFFSET] * S_DATA_WIDTH);
                    s_axi_rresp_int = m_axi_rresp;
                    s_axi_rlast_int = 1'b0;
                    s_axi_ruser_int = m_axi_ruser;
                    s_axi_rvalid_int = 1'b1;
                    burst_next = burst_reg - 1;
                    addr_next = addr_reg + (1 << burst_size_reg);
                    if (burst_reg == 0) begin
                        m_axi_rready_next = 1'b0;
                        s_axi_arready_next = !m_axi_arvalid;
                        s_axi_rlast_int = 1'b1;
                        state_next = STATE_IDLE;
                    end else if (addr_next[master_burst_size_reg] != addr_reg[master_burst_size_reg]) begin
                        state_next = STATE_DATA_READ;
                    end else begin
                        m_axi_rready_next = 1'b0;
                        state_next = STATE_DATA_SPLIT;
                    end
                end else begin
                    state_next = STATE_DATA_READ;
                end
            end
            STATE_DATA_SPLIT: begin
                m_axi_rready_next = 1'b0;

                if (s_axi_rready_int_reg) begin
                    s_axi_rid_int = id_reg;
                    s_axi_rdata_int = data_reg >> (addr_reg[M_ADDR_BIT_OFFSET-1:S_ADDR_BIT_OFFSET] * S_DATA_WIDTH);
                    s_axi_rresp_int = resp_reg;
                    s_axi_rlast_int = 1'b0;
                    s_axi_ruser_int = ruser_reg;
                    s_axi_rvalid_int = 1'b1;
                    burst_next = burst_reg - 1;
                    addr_next = addr_reg + (1 << burst_size_reg);
                    if (burst_reg == 0) begin
                        s_axi_arready_next = !m_axi_arvalid;
                        s_axi_rlast_int = 1'b1;
                        state_next = STATE_IDLE;
                    end else if (addr_next[master_burst_size_reg] != addr_reg[master_burst_size_reg]) begin
                        m_axi_rready_next = s_axi_rready_int_early;
                        state_next = STATE_DATA_READ;
                    end else begin
                        state_next = STATE_DATA_SPLIT;
                    end
                end else begin
                    state_next = STATE_DATA_SPLIT;
                end
            end
        endcase
    end else begin
        // master output is narrower; merge reads and possibly split burst
        s_axi_rid_int = id_reg;
        s_axi_rdata_int = data_reg;
        s_axi_rresp_int = resp_reg;
        s_axi_rlast_int = 1'b0;
        s_axi_ruser_int = m_axi_ruser;
        s_axi_rvalid_int = 0;

        case (state_reg)
            STATE_IDLE: begin
                // idle state; wait for new burst
                s_axi_arready_next = !m_axi_arvalid;

                resp_next = 2'd0;

                if (s_axi_arready && s_axi_arvalid) begin
                    s_axi_arready_next = 1'b0;
                    id_next = s_axi_arid;
                    m_axi_arid_next = s_axi_arid;
                    m_axi_araddr_next = s_axi_araddr;
                    addr_next = s_axi_araddr;
                    burst_next = s_axi_arlen;
                    burst_size_next = s_axi_arsize;
                    if (s_axi_arsize > M_BURST_SIZE) begin
                        // need to adjust burst size
                        if (s_axi_arlen >> (8+M_BURST_SIZE-s_axi_arsize) != 0) begin
                            // limit burst length to max
                            master_burst_next = (8'd255 << (s_axi_arsize-M_BURST_SIZE)) | ((~s_axi_araddr & (8'hff >> (8-s_axi_arsize))) >> M_BURST_SIZE);
                        end else begin
                            master_burst_next = (s_axi_arlen << (s_axi_arsize-M_BURST_SIZE)) | ((~s_axi_araddr & (8'hff >> (8-s_axi_arsize))) >> M_BURST_SIZE);
                        end
                        master_burst_size_next = M_BURST_SIZE;
                        m_axi_arlen_next = master_burst_next;
                        m_axi_arsize_next = master_burst_size_next;
                    end else begin
                        // pass through narrow (enough) burst
                        master_burst_next = s_axi_arlen;
                        master_burst_size_next = s_axi_arsize;
                        m_axi_arlen_next = s_axi_arlen;
                        m_axi_arsize_next = s_axi_arsize;
                    end
                    m_axi_arburst_next = s_axi_arburst;
                    m_axi_arlock_next = s_axi_arlock;
                    m_axi_arcache_next = s_axi_arcache;
                    m_axi_arprot_next = s_axi_arprot;
                    m_axi_arqos_next = s_axi_arqos;
                    m_axi_arregion_next = s_axi_arregion;
                    m_axi_aruser_next = s_axi_aruser;
                    m_axi_arvalid_next = 1'b1;
                    m_axi_rready_next = 1'b0;
                    state_next = STATE_DATA;
                end else begin
                    state_next = STATE_IDLE;
                end
            end
            STATE_DATA: begin
                m_axi_rready_next = s_axi_rready_int_early && !m_axi_arvalid;

                if (m_axi_rready && m_axi_rvalid) begin
                    data_next[addr_reg[S_ADDR_BIT_OFFSET-1:M_ADDR_BIT_OFFSET]*SEGMENT_DATA_WIDTH +: SEGMENT_DATA_WIDTH] = m_axi_rdata;
                    if (m_axi_rresp) begin
                        resp_next = m_axi_rresp;
                    end
                    s_axi_rid_int = id_reg;
                    s_axi_rdata_int = data_next;
                    s_axi_rresp_int = resp_next;
                    s_axi_rlast_int = 1'b0;
                    s_axi_ruser_int = m_axi_ruser;
                    s_axi_rvalid_int = 1'b0;
                    master_burst_next = master_burst_reg - 1;
                    addr_next = (addr_reg + (1 << master_burst_size_reg)) & ({ADDR_WIDTH{1'b1}} << master_burst_size_reg);
                    m_axi_araddr_next = addr_next;
                    if (addr_next[burst_size_reg] != addr_reg[burst_size_reg]) begin
                        data_next = {DATA_WIDTH{1'b0}};
                        burst_next = burst_reg - 1;
                        s_axi_rvalid_int = 1'b1;
                    end
                    if (master_burst_reg == 0) begin
                        if (burst_next >> (8+M_BURST_SIZE-burst_size_reg) != 0) begin
                            // limit burst length to max
                            master_burst_next = 8'd255;
                        end else begin
                            master_burst_next = (burst_next << (burst_size_reg-M_BURST_SIZE)) | (8'hff >> (8-burst_size_reg) >> M_BURST_SIZE);
                        end
                        m_axi_arlen_next = master_burst_next;

                        if (burst_reg == 0) begin
                            m_axi_rready_next = 1'b0;
                            s_axi_rlast_int = 1'b1;
                            s_axi_rvalid_int = 1'b1;
                            s_axi_arready_next = !m_axi_arvalid;
                            state_next = STATE_IDLE;
                        end else begin
                            // start new burst
                            m_axi_arvalid_next = 1'b1;
                            m_axi_rready_next = 1'b0;
                            state_next = STATE_DATA;
                        end
                    end else begin
                        state_next = STATE_DATA;
                    end
                end else begin
                    state_next = STATE_DATA;
                end
            end
        endcase
    end
end

always @(posedge clk) begin
    state_reg <= state_next;

    id_reg <= id_next;
    addr_reg <= addr_next;
    data_reg <= data_next;
    resp_reg <= resp_next;
    ruser_reg <= ruser_next;
    burst_reg <= burst_next;
    burst_size_reg <= burst_size_next;
    master_burst_reg <= master_burst_next;
    master_burst_size_reg <= master_burst_size_next;

    s_axi_arready_reg <= s_axi_arready_next;

    m_axi_arid_reg <= m_axi_arid_next;
    m_axi_araddr_reg <= m_axi_araddr_next;
    m_axi_arlen_reg <= m_axi_arlen_next;
    m_axi_arsize_reg <= m_axi_arsize_next;
    m_axi_arburst_reg <= m_axi_arburst_next;
    m_axi_arlock_reg <= m_axi_arlock_next;
    m_axi_arcache_reg <= m_axi_arcache_next;
    m_axi_arprot_reg <= m_axi_arprot_next;
    m_axi_arqos_reg <= m_axi_arqos_next;
    m_axi_arregion_reg <= m_axi_arregion_next;
    m_axi_aruser_reg <= m_axi_aruser_next;
    m_axi_arvalid_reg <= m_axi_arvalid_next;
    m_axi_rready_reg <= m_axi_rready_next;

    if (rst) begin
        state_reg <= STATE_IDLE;

        s_axi_arready_reg <= 1'b0;

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

// output datapath logic
reg [ID_WIDTH-1:0]     s_axi_rid_reg    = {ID_WIDTH{1'b0}};
reg [S_DATA_WIDTH-1:0] s_axi_rdata_reg  = {S_DATA_WIDTH{1'b0}};
reg [1:0]              s_axi_rresp_reg  = 2'd0;
reg                    s_axi_rlast_reg  = 1'b0;
reg [RUSER_WIDTH-1:0]  s_axi_ruser_reg  = 1'b0;
reg                    s_axi_rvalid_reg = 1'b0, s_axi_rvalid_next;

reg [ID_WIDTH-1:0]     temp_s_axi_rid_reg    = {ID_WIDTH{1'b0}};
reg [S_DATA_WIDTH-1:0] temp_s_axi_rdata_reg  = {S_DATA_WIDTH{1'b0}};
reg [1:0]              temp_s_axi_rresp_reg  = 2'd0;
reg                    temp_s_axi_rlast_reg  = 1'b0;
reg [RUSER_WIDTH-1:0]  temp_s_axi_ruser_reg  = 1'b0;
reg                    temp_s_axi_rvalid_reg = 1'b0, temp_s_axi_rvalid_next;

// datapath control
reg store_axi_r_int_to_output;
reg store_axi_r_int_to_temp;
reg store_axi_r_temp_to_output;

assign s_axi_rid    = s_axi_rid_reg;
assign s_axi_rdata  = s_axi_rdata_reg;
assign s_axi_rresp  = s_axi_rresp_reg;
assign s_axi_rlast  = s_axi_rlast_reg;
assign s_axi_ruser  = RUSER_ENABLE ? s_axi_ruser_reg : {RUSER_WIDTH{1'b0}};
assign s_axi_rvalid = s_axi_rvalid_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 s_axi_rready_int_early = s_axi_rready | (~temp_s_axi_rvalid_reg & (~s_axi_rvalid_reg | ~s_axi_rvalid_int));

always @* begin
    // transfer sink ready state to source
    s_axi_rvalid_next = s_axi_rvalid_reg;
    temp_s_axi_rvalid_next = temp_s_axi_rvalid_reg;

    store_axi_r_int_to_output = 1'b0;
    store_axi_r_int_to_temp = 1'b0;
    store_axi_r_temp_to_output = 1'b0;

    if (s_axi_rready_int_reg) begin
        // input is ready
        if (s_axi_rready | ~s_axi_rvalid_reg) begin
            // output is ready or currently not valid, transfer data to output
            s_axi_rvalid_next = s_axi_rvalid_int;
            store_axi_r_int_to_output = 1'b1;
        end else begin
            // output is not ready, store input in temp
            temp_s_axi_rvalid_next = s_axi_rvalid_int;
            store_axi_r_int_to_temp = 1'b1;
        end
    end else if (s_axi_rready) begin
        // input is not ready, but output is ready
        s_axi_rvalid_next = temp_s_axi_rvalid_reg;
        temp_s_axi_rvalid_next = 1'b0;
        store_axi_r_temp_to_output = 1'b1;
    end
end

always @(posedge clk) begin
    if (rst) begin
        s_axi_rvalid_reg <= 1'b0;
        s_axi_rready_int_reg <= 1'b0;
        temp_s_axi_rvalid_reg <= 1'b0;
    end else begin
        s_axi_rvalid_reg <= s_axi_rvalid_next;
        s_axi_rready_int_reg <= s_axi_rready_int_early;
        temp_s_axi_rvalid_reg <= temp_s_axi_rvalid_next;
    end

    // datapath
    if (store_axi_r_int_to_output) begin
        s_axi_rid_reg <= s_axi_rid_int;
        s_axi_rdata_reg <= s_axi_rdata_int;
        s_axi_rresp_reg <= s_axi_rresp_int;
        s_axi_rlast_reg <= s_axi_rlast_int;
        s_axi_ruser_reg <= s_axi_ruser_int;
    end else if (store_axi_r_temp_to_output) begin
        s_axi_rid_reg <= temp_s_axi_rid_reg;
        s_axi_rdata_reg <= temp_s_axi_rdata_reg;
        s_axi_rresp_reg <= temp_s_axi_rresp_reg;
        s_axi_rlast_reg <= temp_s_axi_rlast_reg;
        s_axi_ruser_reg <= temp_s_axi_ruser_reg;
    end

    if (store_axi_r_int_to_temp) begin
        temp_s_axi_rid_reg <= s_axi_rid_int;
        temp_s_axi_rdata_reg <= s_axi_rdata_int;
        temp_s_axi_rresp_reg <= s_axi_rresp_int;
        temp_s_axi_rlast_reg <= s_axi_rlast_int;
        temp_s_axi_ruser_reg <= s_axi_ruser_int;
    end
end

endmodule