module axil_adapter_wr #
(
    // 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)
)
(
    input  wire                     clk,
    input  wire                     rst,

    /*
     * AXI lite slave interface
     */
    input  wire [ADDR_WIDTH-1:0]    s_axil_awaddr,
    input  wire [2:0]               s_axil_awprot,
    input  wire                     s_axil_awvalid,
    output wire                     s_axil_awready,
    input  wire [S_DATA_WIDTH-1:0]  s_axil_wdata,
    input  wire [S_STRB_WIDTH-1:0]  s_axil_wstrb,
    input  wire                     s_axil_wvalid,
    output wire                     s_axil_wready,
    output wire [1:0]               s_axil_bresp,
    output wire                     s_axil_bvalid,
    input  wire                     s_axil_bready,

    /*
     * AXI lite master interface
     */
    output wire [ADDR_WIDTH-1:0]    m_axil_awaddr,
    output wire [2:0]               m_axil_awprot,
    output wire                     m_axil_awvalid,
    input  wire                     m_axil_awready,
    output wire [M_DATA_WIDTH-1:0]  m_axil_wdata,
    output wire [M_STRB_WIDTH-1:0]  m_axil_wstrb,
    output wire                     m_axil_wvalid,
    input  wire                     m_axil_wready,
    input  wire [1:0]               m_axil_bresp,
    input  wire                     m_axil_bvalid,
    output wire                     m_axil_bready
);

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_ADDR_MASK = {ADDR_WIDTH{1'b1}} << S_ADDR_BIT_OFFSET;
parameter M_ADDR_MASK = {ADDR_WIDTH{1'b1}} << M_ADDR_BIT_OFFSET;

// 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);
parameter SEGMENT_COUNT_WIDTH = SEGMENT_COUNT == 1 ? 1 : $clog2(SEGMENT_COUNT);
// 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_RESP = 2'd3;

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

reg [DATA_WIDTH-1:0] data_reg = {DATA_WIDTH{1'b0}}, data_next;
reg [STRB_WIDTH-1:0] strb_reg = {STRB_WIDTH{1'b0}}, strb_next;

reg [SEGMENT_COUNT_WIDTH-1:0] current_segment_reg = 0, current_segment_next;

reg s_axil_awready_reg = 1'b0, s_axil_awready_next;
reg s_axil_wready_reg = 1'b0, s_axil_wready_next;
reg [1:0] s_axil_bresp_reg = 2'd0, s_axil_bresp_next;
reg s_axil_bvalid_reg = 1'b0, s_axil_bvalid_next;

reg [ADDR_WIDTH-1:0] m_axil_awaddr_reg = {ADDR_WIDTH{1'b0}}, m_axil_awaddr_next;
reg [2:0] m_axil_awprot_reg = 3'd0, m_axil_awprot_next;
reg m_axil_awvalid_reg = 1'b0, m_axil_awvalid_next;
reg [M_DATA_WIDTH-1:0] m_axil_wdata_reg = {M_DATA_WIDTH{1'b0}}, m_axil_wdata_next;
reg [M_STRB_WIDTH-1:0] m_axil_wstrb_reg = {M_STRB_WIDTH{1'b0}}, m_axil_wstrb_next;
reg m_axil_wvalid_reg = 1'b0, m_axil_wvalid_next;
reg m_axil_bready_reg = 1'b0, m_axil_bready_next;

assign s_axil_awready = s_axil_awready_reg;
assign s_axil_wready = s_axil_wready_reg;
assign s_axil_bresp = s_axil_bresp_reg;
assign s_axil_bvalid = s_axil_bvalid_reg;

assign m_axil_awaddr = m_axil_awaddr_reg;
assign m_axil_awprot = m_axil_awprot_reg;
assign m_axil_awvalid = m_axil_awvalid_reg;
assign m_axil_wdata = m_axil_wdata_reg;
assign m_axil_wstrb = m_axil_wstrb_reg;
assign m_axil_wvalid = m_axil_wvalid_reg;
assign m_axil_bready = m_axil_bready_reg;

always @* begin
    state_next = STATE_IDLE;

    data_next = data_reg;
    strb_next = strb_reg;

    current_segment_next = current_segment_reg;

    s_axil_awready_next = 1'b0;
    s_axil_wready_next = 1'b0;
    s_axil_bresp_next = s_axil_bresp_reg;
    s_axil_bvalid_next = s_axil_bvalid_reg && !s_axil_bready;
    m_axil_awaddr_next = m_axil_awaddr_reg;
    m_axil_awprot_next = m_axil_awprot_reg;
    m_axil_awvalid_next = m_axil_awvalid_reg && !m_axil_awready;
    m_axil_wdata_next = m_axil_wdata_reg;
    m_axil_wstrb_next = m_axil_wstrb_reg;
    m_axil_wvalid_next = m_axil_wvalid_reg && !m_axil_wready;
    m_axil_bready_next = 1'b0;

    if (SEGMENT_COUNT == 1 || EXPAND) begin
        // master output is same width or wider; single cycle direct transfer
        case (state_reg)
            STATE_IDLE: begin
                s_axil_awready_next = !m_axil_awvalid;

                if (s_axil_awready && s_axil_awvalid) begin
                    s_axil_awready_next = 1'b0;
                    m_axil_awaddr_next = s_axil_awaddr;
                    m_axil_awprot_next = s_axil_awprot;
                    m_axil_awvalid_next = 1'b1;
                    s_axil_wready_next = !m_axil_wvalid;
                    state_next = STATE_DATA;
                end else begin
                    state_next = STATE_IDLE;
                end
            end
            STATE_DATA: begin
                s_axil_wready_next = !m_axil_wvalid;

                if (s_axil_wready && s_axil_wvalid) begin
                    s_axil_wready_next = 1'b0;
                    if (M_WORD_WIDTH == S_WORD_WIDTH) begin
                        m_axil_wdata_next = s_axil_wdata;
                        m_axil_wstrb_next = s_axil_wstrb;
                    end else begin
                        m_axil_wdata_next = {(M_WORD_WIDTH/S_WORD_WIDTH){s_axil_wdata}};
                        m_axil_wstrb_next = s_axil_wstrb << (m_axil_awaddr_reg[M_ADDR_BIT_OFFSET - 1:S_ADDR_BIT_OFFSET] * S_STRB_WIDTH);
                    end
                    m_axil_wvalid_next = 1'b1;
                    m_axil_bready_next = !s_axil_bvalid;
                    state_next = STATE_RESP;
                end else begin
                    state_next = STATE_DATA;
                end
            end
            STATE_RESP: begin
                m_axil_bready_next = !s_axil_bvalid;

                if (m_axil_bready && m_axil_bvalid) begin
                    m_axil_bready_next = 1'b0;
                    s_axil_bresp_next = m_axil_bresp;
                    s_axil_bvalid_next = 1'b1;
                    s_axil_awready_next = !m_axil_awvalid;
                    state_next = STATE_IDLE;
                end else begin
                    state_next = STATE_RESP;
                end
            end
        endcase
    end else begin
        // master output is narrower; may need several cycles
        case (state_reg)
            STATE_IDLE: begin
                s_axil_awready_next = !m_axil_awvalid;

                current_segment_next = s_axil_awaddr >> M_ADDR_BIT_OFFSET;
                s_axil_bresp_next = 2'd0;

                if (s_axil_awready && s_axil_awvalid) begin
                    s_axil_awready_next = 1'b0;
                    m_axil_awaddr_next = s_axil_awaddr;
                    m_axil_awprot_next = s_axil_awprot;
                    m_axil_awvalid_next = 1'b1;
                    s_axil_wready_next = !m_axil_wvalid;
                    state_next = STATE_DATA;
                end else begin
                    state_next = STATE_IDLE;
                end
            end
            STATE_DATA: begin
                s_axil_wready_next = !m_axil_wvalid;

                if (s_axil_wready && s_axil_wvalid) begin
                    s_axil_wready_next = 1'b0;
                    data_next = s_axil_wdata;
                    strb_next = s_axil_wstrb;
                    m_axil_wdata_next = data_next >> current_segment_reg*SEGMENT_DATA_WIDTH;
                    m_axil_wstrb_next = strb_next >> current_segment_reg*SEGMENT_STRB_WIDTH;
                    m_axil_wvalid_next = 1'b1;
                    m_axil_bready_next = !s_axil_bvalid;
                    current_segment_next = current_segment_reg + 1;
                    state_next = STATE_RESP;
                end else begin
                    state_next = STATE_DATA;
                end
            end
            STATE_RESP: begin
                m_axil_bready_next = !s_axil_bvalid;

                if (m_axil_bready && m_axil_bvalid) begin
                    m_axil_bready_next = 1'b0;
                    m_axil_awaddr_next = (m_axil_awaddr_reg & M_ADDR_MASK) + SEGMENT_STRB_WIDTH;
                    m_axil_wdata_next = data_next >> current_segment_reg*SEGMENT_DATA_WIDTH;
                    m_axil_wstrb_next = strb_next >> current_segment_reg*SEGMENT_STRB_WIDTH;
                    current_segment_next = current_segment_reg + 1;
                    if (m_axil_bresp != 0) begin
                        s_axil_bresp_next = m_axil_bresp;
                    end
                    if (current_segment_reg == 0) begin
                        s_axil_bvalid_next = 1'b1;
                        s_axil_awready_next = !m_axil_awvalid;
                        state_next = STATE_IDLE;
                    end else begin
                        m_axil_awvalid_next = 1'b1;
                        m_axil_wvalid_next = 1'b1;
                        state_next = STATE_RESP;
                    end
                end else begin
                    state_next = STATE_RESP;
                end
            end
        endcase
    end
end

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

    data_reg <= data_next;
    strb_reg <= strb_next;

    current_segment_reg <= current_segment_next;

    s_axil_awready_reg <= s_axil_awready_next;
    s_axil_wready_reg <= s_axil_wready_next;
    s_axil_bresp_reg <= s_axil_bresp_next;
    s_axil_bvalid_reg <= s_axil_bvalid_next;

    m_axil_awaddr_reg <= m_axil_awaddr_next;
    m_axil_awprot_reg <= m_axil_awprot_next;
    m_axil_awvalid_reg <= m_axil_awvalid_next;
    m_axil_wdata_reg <= m_axil_wdata_next;
    m_axil_wstrb_reg <= m_axil_wstrb_next;
    m_axil_wvalid_reg <= m_axil_wvalid_next;
    m_axil_bready_reg <= m_axil_bready_next;

    if (rst) begin
        state_reg <= STATE_IDLE;

        s_axil_awready_reg <= 1'b0;
        s_axil_wready_reg <= 1'b0;
        s_axil_bvalid_reg <= 1'b0;

        m_axil_awvalid_reg <= 1'b0;
        m_axil_wvalid_reg <= 1'b0;
        m_axil_bready_reg <= 1'b0;
    end
end

endmodule