module axi_ram_rd_if #
(
    // Width of data bus in bits
    parameter DATA_WIDTH = 32,
    // Width of address bus in bits
    parameter ADDR_WIDTH = 16,
    // Width of wstrb (width of data bus in words)
    parameter STRB_WIDTH = (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,
    // Extra pipeline register on output
    parameter PIPELINE_OUTPUT = 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 [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,

    /*
     * RAM interface
     */
    output wire [ID_WIDTH-1:0]      ram_rd_cmd_id,
    output wire [ADDR_WIDTH-1:0]    ram_rd_cmd_addr,
    output wire                     ram_rd_cmd_lock,
    output wire [3:0]               ram_rd_cmd_cache,
    output wire [2:0]               ram_rd_cmd_prot,
    output wire [3:0]               ram_rd_cmd_qos,
    output wire [3:0]               ram_rd_cmd_region,
    output wire [ARUSER_WIDTH-1:0]  ram_rd_cmd_auser,
    output wire                     ram_rd_cmd_en,
    output wire                     ram_rd_cmd_last,
    input  wire                     ram_rd_cmd_ready,
    input  wire [ID_WIDTH-1:0]      ram_rd_resp_id,
    input  wire [DATA_WIDTH-1:0]    ram_rd_resp_data,
    input  wire                     ram_rd_resp_last,
    input  wire [RUSER_WIDTH-1:0]   ram_rd_resp_user,
    input  wire                     ram_rd_resp_valid,
    output wire                     ram_rd_resp_ready
);

parameter VALID_ADDR_WIDTH = ADDR_WIDTH - $clog2(STRB_WIDTH);
parameter WORD_WIDTH = STRB_WIDTH;
parameter WORD_SIZE = DATA_WIDTH/WORD_WIDTH;

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

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

localparam [0:0]
    STATE_IDLE = 1'd0,
    STATE_BURST = 1'd1;

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

reg [ID_WIDTH-1:0] read_id_reg = {ID_WIDTH{1'b0}}, read_id_next;
reg [ADDR_WIDTH-1:0] read_addr_reg = {ADDR_WIDTH{1'b0}}, read_addr_next;
reg read_lock_reg = 1'b0, read_lock_next;
reg [3:0] read_cache_reg = 4'd0, read_cache_next;
reg [2:0] read_prot_reg = 3'd0, read_prot_next;
reg [3:0] read_qos_reg = 4'd0, read_qos_next;
reg [3:0] read_region_reg = 4'd0, read_region_next;
reg [ARUSER_WIDTH-1:0] read_aruser_reg = {ARUSER_WIDTH{1'b0}}, read_aruser_next;
reg read_addr_valid_reg = 1'b0, read_addr_valid_next;
reg read_last_reg = 1'b0, read_last_next;
reg [7:0] read_count_reg = 8'd0, read_count_next;
reg [2:0] read_size_reg = 3'd0, read_size_next;
reg [1:0] read_burst_reg = 2'd0, read_burst_next;

reg s_axi_arready_reg = 1'b0, s_axi_arready_next;
reg [ID_WIDTH-1:0] s_axi_rid_pipe_reg = {ID_WIDTH{1'b0}};
reg [DATA_WIDTH-1:0] s_axi_rdata_pipe_reg = {DATA_WIDTH{1'b0}};
reg s_axi_rlast_pipe_reg = 1'b0;
reg [RUSER_WIDTH-1:0] s_axi_ruser_pipe_reg = {RUSER_WIDTH{1'b0}};
reg s_axi_rvalid_pipe_reg = 1'b0;

assign s_axi_arready = s_axi_arready_reg;
assign s_axi_rid = PIPELINE_OUTPUT ? s_axi_rid_pipe_reg : ram_rd_resp_id;
assign s_axi_rdata = PIPELINE_OUTPUT ? s_axi_rdata_pipe_reg : ram_rd_resp_data;
assign s_axi_rresp = 2'b00;
assign s_axi_rlast = PIPELINE_OUTPUT ? s_axi_rlast_pipe_reg : ram_rd_resp_last;
assign s_axi_ruser = PIPELINE_OUTPUT ? s_axi_ruser_pipe_reg : ram_rd_resp_user;
assign s_axi_rvalid = PIPELINE_OUTPUT ? s_axi_rvalid_pipe_reg : ram_rd_resp_valid;

assign ram_rd_cmd_id = read_id_reg;
assign ram_rd_cmd_addr = read_addr_reg;
assign ram_rd_cmd_lock = read_lock_reg;
assign ram_rd_cmd_cache = read_cache_reg;
assign ram_rd_cmd_prot = read_prot_reg;
assign ram_rd_cmd_qos = read_qos_reg;
assign ram_rd_cmd_region = read_region_reg;
assign ram_rd_cmd_auser = ARUSER_ENABLE ? read_aruser_reg : {ARUSER_WIDTH{1'b0}};
assign ram_rd_cmd_en = read_addr_valid_reg;
assign ram_rd_cmd_last = read_last_reg;

assign ram_rd_resp_ready = s_axi_rready || (PIPELINE_OUTPUT && !s_axi_rvalid_pipe_reg);

always @* begin
    state_next = STATE_IDLE;

    read_id_next = read_id_reg;
    read_addr_next = read_addr_reg;
    read_lock_next = read_lock_reg;
    read_cache_next = read_cache_reg;
    read_prot_next = read_prot_reg;
    read_qos_next = read_qos_reg;
    read_region_next = read_region_reg;
    read_aruser_next = read_aruser_reg;
    read_addr_valid_next = read_addr_valid_reg && !ram_rd_cmd_ready;
    read_last_next = read_last_reg;
    read_count_next = read_count_reg;
    read_size_next = read_size_reg;
    read_burst_next = read_burst_reg;

    s_axi_arready_next = 1'b0;

    case (state_reg)
        STATE_IDLE: begin
            s_axi_arready_next = 1'b1;

            if (s_axi_arready && s_axi_arvalid) begin
                read_id_next = s_axi_arid;
                read_addr_next = s_axi_araddr;
                read_lock_next = s_axi_arlock;
                read_cache_next = s_axi_arcache;
                read_prot_next = s_axi_arprot;
                read_qos_next = s_axi_arqos;
                read_region_next = s_axi_arregion;
                read_aruser_next = s_axi_aruser;
                read_count_next = s_axi_arlen;
                read_size_next = s_axi_arsize < $clog2(STRB_WIDTH) ? s_axi_arsize : $clog2(STRB_WIDTH);
                read_burst_next = s_axi_arburst;

                s_axi_arready_next = 1'b0;
                read_last_next = read_count_next == 0;
                read_addr_valid_next = 1'b1;
                state_next = STATE_BURST;
            end else begin
                state_next = STATE_IDLE;
            end
        end
        STATE_BURST: begin
            if (ram_rd_cmd_ready && ram_rd_cmd_en) begin
                if (read_burst_reg != 2'b00) begin
                    read_addr_next = read_addr_reg + (1 << read_size_reg);
                end
                read_count_next = read_count_reg - 1;
                read_last_next = read_count_next == 0;
                if (read_count_reg > 0) begin
                    read_addr_valid_next = 1'b1;
                    state_next = STATE_BURST;
                end else begin
                    s_axi_arready_next = 1'b1;
                    state_next = STATE_IDLE;
                end
            end else begin
                state_next = STATE_BURST;
            end
        end
    endcase
end

always @(posedge clk) begin
    if (rst) begin
        state_reg <= STATE_IDLE;
        read_addr_valid_reg <= 1'b0;
        s_axi_arready_reg <= 1'b0;
        s_axi_rvalid_pipe_reg <= 1'b0;
    end else begin
        state_reg <= state_next;
        read_addr_valid_reg <= read_addr_valid_next;
        s_axi_arready_reg <= s_axi_arready_next;

        if (!s_axi_rvalid_pipe_reg || s_axi_rready) begin
            s_axi_rvalid_pipe_reg <= ram_rd_resp_valid;
        end
    end

    read_id_reg <= read_id_next;
    read_addr_reg <= read_addr_next;
    read_lock_reg <= read_lock_next;
    read_cache_reg <= read_cache_next;
    read_prot_reg <= read_prot_next;
    read_qos_reg <= read_qos_next;
    read_region_reg <= read_region_next;
    read_aruser_reg <= read_aruser_next;
    read_last_reg <= read_last_next;
    read_count_reg <= read_count_next;
    read_size_reg <= read_size_next;
    read_burst_reg <= read_burst_next;

    if (!s_axi_rvalid_pipe_reg || s_axi_rready) begin
        s_axi_rid_pipe_reg <= ram_rd_resp_id;
        s_axi_rdata_pipe_reg <= ram_rd_resp_data;
        s_axi_rlast_pipe_reg <= ram_rd_resp_last;
        s_axi_ruser_pipe_reg <= ram_rd_resp_user;
    end
end

endmodule