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[/] [spacewiresystemc/] [trunk/] [altera_work/] [spw_fifo_ulight/] [ulight_fifo/] [synthesis/] [submodules/] [altera_avalon_sc_fifo.v] - Rev 40
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// ----------------------------------------------------------- // Legal Notice: (C)2007 Altera Corporation. All rights reserved. Your // use of Altera Corporation's design tools, logic functions and other // software and tools, and its AMPP partner logic functions, and any // output files any of the foregoing (including device programming or // simulation files), and any associated documentation or information are // expressly subject to the terms and conditions of the Altera Program // License Subscription Agreement or other applicable license agreement, // including, without limitation, that your use is for the sole purpose // of programming logic devices manufactured by Altera and sold by Altera // or its authorized distributors. Please refer to the applicable // agreement for further details. // // Description: Single clock Avalon-ST FIFO. // ----------------------------------------------------------- `timescale 1 ns / 1 ns //altera message_off 10036 module altera_avalon_sc_fifo #( // -------------------------------------------------- // Parameters // -------------------------------------------------- parameter SYMBOLS_PER_BEAT = 1, parameter BITS_PER_SYMBOL = 8, parameter FIFO_DEPTH = 16, parameter CHANNEL_WIDTH = 0, parameter ERROR_WIDTH = 0, parameter USE_PACKETS = 0, parameter USE_FILL_LEVEL = 0, parameter USE_STORE_FORWARD = 0, parameter USE_ALMOST_FULL_IF = 0, parameter USE_ALMOST_EMPTY_IF = 0, // -------------------------------------------------- // Empty latency is defined as the number of cycles // required for a write to deassert the empty flag. // For example, a latency of 1 means that the empty // flag is deasserted on the cycle after a write. // // Another way to think of it is the latency for a // write to propagate to the output. // // An empty latency of 0 implies lookahead, which is // only implemented for the register-based FIFO. // -------------------------------------------------- parameter EMPTY_LATENCY = 3, parameter USE_MEMORY_BLOCKS = 1, // -------------------------------------------------- // Internal Parameters // -------------------------------------------------- parameter DATA_WIDTH = SYMBOLS_PER_BEAT * BITS_PER_SYMBOL, parameter EMPTY_WIDTH = log2ceil(SYMBOLS_PER_BEAT) ) ( // -------------------------------------------------- // Ports // -------------------------------------------------- input clk, input reset, input [DATA_WIDTH-1: 0] in_data, input in_valid, input in_startofpacket, input in_endofpacket, input [((EMPTY_WIDTH>0) ? (EMPTY_WIDTH-1):0) : 0] in_empty, input [((ERROR_WIDTH>0) ? (ERROR_WIDTH-1):0) : 0] in_error, input [((CHANNEL_WIDTH>0) ? (CHANNEL_WIDTH-1):0): 0] in_channel, output in_ready, output [DATA_WIDTH-1 : 0] out_data, output reg out_valid, output out_startofpacket, output out_endofpacket, output [((EMPTY_WIDTH>0) ? (EMPTY_WIDTH-1):0) : 0] out_empty, output [((ERROR_WIDTH>0) ? (ERROR_WIDTH-1):0) : 0] out_error, output [((CHANNEL_WIDTH>0) ? (CHANNEL_WIDTH-1):0): 0] out_channel, input out_ready, input [(USE_STORE_FORWARD ? 2 : 1) : 0] csr_address, input csr_write, input csr_read, input [31 : 0] csr_writedata, output reg [31 : 0] csr_readdata, output wire almost_full_data, output wire almost_empty_data ); // -------------------------------------------------- // Local Parameters // -------------------------------------------------- localparam ADDR_WIDTH = log2ceil(FIFO_DEPTH); localparam DEPTH = FIFO_DEPTH; localparam PKT_SIGNALS_WIDTH = 2 + EMPTY_WIDTH; localparam PAYLOAD_WIDTH = (USE_PACKETS == 1) ? 2 + EMPTY_WIDTH + DATA_WIDTH + ERROR_WIDTH + CHANNEL_WIDTH: DATA_WIDTH + ERROR_WIDTH + CHANNEL_WIDTH; // -------------------------------------------------- // Internal Signals // -------------------------------------------------- genvar i; reg [PAYLOAD_WIDTH-1 : 0] mem [DEPTH-1 : 0]; reg [ADDR_WIDTH-1 : 0] wr_ptr; reg [ADDR_WIDTH-1 : 0] rd_ptr; reg [DEPTH-1 : 0] mem_used; wire [ADDR_WIDTH-1 : 0] next_wr_ptr; wire [ADDR_WIDTH-1 : 0] next_rd_ptr; wire [ADDR_WIDTH-1 : 0] incremented_wr_ptr; wire [ADDR_WIDTH-1 : 0] incremented_rd_ptr; wire [ADDR_WIDTH-1 : 0] mem_rd_ptr; wire read; wire write; reg empty; reg next_empty; reg full; reg next_full; wire [PKT_SIGNALS_WIDTH-1 : 0] in_packet_signals; wire [PKT_SIGNALS_WIDTH-1 : 0] out_packet_signals; wire [PAYLOAD_WIDTH-1 : 0] in_payload; reg [PAYLOAD_WIDTH-1 : 0] internal_out_payload; reg [PAYLOAD_WIDTH-1 : 0] out_payload; reg internal_out_valid; wire internal_out_ready; reg [ADDR_WIDTH : 0] fifo_fill_level; reg [ADDR_WIDTH : 0] fill_level; reg [ADDR_WIDTH-1 : 0] sop_ptr = 0; wire [ADDR_WIDTH-1 : 0] curr_sop_ptr; reg [23:0] almost_full_threshold; reg [23:0] almost_empty_threshold; reg [23:0] cut_through_threshold; reg [15:0] pkt_cnt; reg drop_on_error_en; reg error_in_pkt; reg pkt_has_started; reg sop_has_left_fifo; reg fifo_too_small_r; reg pkt_cnt_eq_zero; reg pkt_cnt_eq_one; wire wait_for_threshold; reg pkt_mode; wire wait_for_pkt; wire ok_to_forward; wire in_pkt_eop_arrive; wire out_pkt_leave; wire in_pkt_start; wire in_pkt_error; wire drop_on_error; wire fifo_too_small; wire out_pkt_sop_leave; wire [31:0] max_fifo_size; reg fifo_fill_level_lt_cut_through_threshold; // -------------------------------------------------- // Define Payload // // Icky part where we decide which signals form the // payload to the FIFO with generate blocks. // -------------------------------------------------- generate if (EMPTY_WIDTH > 0) begin : gen_blk1 assign in_packet_signals = {in_startofpacket, in_endofpacket, in_empty}; assign {out_startofpacket, out_endofpacket, out_empty} = out_packet_signals; end else begin : gen_blk1_else assign out_empty = in_error; assign in_packet_signals = {in_startofpacket, in_endofpacket}; assign {out_startofpacket, out_endofpacket} = out_packet_signals; end endgenerate generate if (USE_PACKETS) begin : gen_blk2 if (ERROR_WIDTH > 0) begin : gen_blk3 if (CHANNEL_WIDTH > 0) begin : gen_blk4 assign in_payload = {in_packet_signals, in_data, in_error, in_channel}; assign {out_packet_signals, out_data, out_error, out_channel} = out_payload; end else begin : gen_blk4_else assign out_channel = in_channel; assign in_payload = {in_packet_signals, in_data, in_error}; assign {out_packet_signals, out_data, out_error} = out_payload; end end else begin : gen_blk3_else assign out_error = in_error; if (CHANNEL_WIDTH > 0) begin : gen_blk5 assign in_payload = {in_packet_signals, in_data, in_channel}; assign {out_packet_signals, out_data, out_channel} = out_payload; end else begin : gen_blk5_else assign out_channel = in_channel; assign in_payload = {in_packet_signals, in_data}; assign {out_packet_signals, out_data} = out_payload; end end end else begin : gen_blk2_else assign out_packet_signals = 0; if (ERROR_WIDTH > 0) begin : gen_blk6 if (CHANNEL_WIDTH > 0) begin : gen_blk7 assign in_payload = {in_data, in_error, in_channel}; assign {out_data, out_error, out_channel} = out_payload; end else begin : gen_blk7_else assign out_channel = in_channel; assign in_payload = {in_data, in_error}; assign {out_data, out_error} = out_payload; end end else begin : gen_blk6_else assign out_error = in_error; if (CHANNEL_WIDTH > 0) begin : gen_blk8 assign in_payload = {in_data, in_channel}; assign {out_data, out_channel} = out_payload; end else begin : gen_blk8_else assign out_channel = in_channel; assign in_payload = in_data; assign out_data = out_payload; end end end endgenerate // -------------------------------------------------- // Memory-based FIFO storage // // To allow a ready latency of 0, the read index is // obtained from the next read pointer and memory // outputs are unregistered. // // If the empty latency is 1, we infer bypass logic // around the memory so writes propagate to the // outputs on the next cycle. // // Do not change the way this is coded: Quartus needs // a perfect match to the template, and any attempt to // refactor the two always blocks into one will break // memory inference. // -------------------------------------------------- generate if (USE_MEMORY_BLOCKS == 1) begin : gen_blk9 if (EMPTY_LATENCY == 1) begin : gen_blk10 always @(posedge clk) begin if (in_valid && in_ready) mem[wr_ptr] = in_payload; internal_out_payload = mem[mem_rd_ptr]; end end else begin : gen_blk10_else always @(posedge clk) begin if (in_valid && in_ready) mem[wr_ptr] <= in_payload; internal_out_payload <= mem[mem_rd_ptr]; end end assign mem_rd_ptr = next_rd_ptr; end else begin : gen_blk9_else // -------------------------------------------------- // Register-based FIFO storage // // Uses a shift register as the storage element. Each // shift register slot has a bit which indicates if // the slot is occupied (credit to Sam H for the idea). // The occupancy bits are contiguous and start from the // lsb, so 0000, 0001, 0011, 0111, 1111 for a 4-deep // FIFO. // // Each slot is enabled during a read or when it // is unoccupied. New data is always written to every // going-to-be-empty slot (we keep track of which ones // are actually useful with the occupancy bits). On a // read we shift occupied slots. // // The exception is the last slot, which always gets // new data when it is unoccupied. // -------------------------------------------------- for (i = 0; i < DEPTH-1; i = i + 1) begin : shift_reg always @(posedge clk or posedge reset) begin if (reset) begin mem[i] <= 0; end else if (read || !mem_used[i]) begin if (!mem_used[i+1]) mem[i] <= in_payload; else mem[i] <= mem[i+1]; end end end always @(posedge clk, posedge reset) begin if (reset) begin mem[DEPTH-1] <= 0; end else begin if (DEPTH == 1) begin if (write) mem[DEPTH-1] <= in_payload; end else if (!mem_used[DEPTH-1]) mem[DEPTH-1] <= in_payload; end end end endgenerate assign read = internal_out_ready && internal_out_valid && ok_to_forward; assign write = in_ready && in_valid; // -------------------------------------------------- // Pointer Management // -------------------------------------------------- generate if (USE_MEMORY_BLOCKS == 1) begin : gen_blk11 assign incremented_wr_ptr = wr_ptr + 1'b1; assign incremented_rd_ptr = rd_ptr + 1'b1; assign next_wr_ptr = drop_on_error ? curr_sop_ptr : write ? incremented_wr_ptr : wr_ptr; assign next_rd_ptr = (read) ? incremented_rd_ptr : rd_ptr; always @(posedge clk or posedge reset) begin if (reset) begin wr_ptr <= 0; rd_ptr <= 0; end else begin wr_ptr <= next_wr_ptr; rd_ptr <= next_rd_ptr; end end end else begin : gen_blk11_else // -------------------------------------------------- // Shift Register Occupancy Bits // // Consider a 4-deep FIFO with 2 entries: 0011 // On a read and write, do not modify the bits. // On a write, left-shift the bits to get 0111. // On a read, right-shift the bits to get 0001. // // Also, on a write we set bit0 (the head), while // clearing the tail on a read. // -------------------------------------------------- always @(posedge clk or posedge reset) begin if (reset) begin mem_used[0] <= 0; end else begin if (write ^ read) begin if (write) mem_used[0] <= 1; else if (read) begin if (DEPTH > 1) mem_used[0] <= mem_used[1]; else mem_used[0] <= 0; end end end end if (DEPTH > 1) begin : gen_blk12 always @(posedge clk or posedge reset) begin if (reset) begin mem_used[DEPTH-1] <= 0; end else begin if (write ^ read) begin mem_used[DEPTH-1] <= 0; if (write) mem_used[DEPTH-1] <= mem_used[DEPTH-2]; end end end end for (i = 1; i < DEPTH-1; i = i + 1) begin : storage_logic always @(posedge clk, posedge reset) begin if (reset) begin mem_used[i] <= 0; end else begin if (write ^ read) begin if (write) mem_used[i] <= mem_used[i-1]; else if (read) mem_used[i] <= mem_used[i+1]; end end end end end endgenerate // -------------------------------------------------- // Memory FIFO Status Management // // Generates the full and empty signals from the // pointers. The FIFO is full when the next write // pointer will be equal to the read pointer after // a write. Reading from a FIFO clears full. // // The FIFO is empty when the next read pointer will // be equal to the write pointer after a read. Writing // to a FIFO clears empty. // // A simultaneous read and write must not change any of // the empty or full flags unless there is a drop on error event. // -------------------------------------------------- generate if (USE_MEMORY_BLOCKS == 1) begin : gen_blk13 always @* begin next_full = full; next_empty = empty; if (read && !write) begin next_full = 1'b0; if (incremented_rd_ptr == wr_ptr) next_empty = 1'b1; end if (write && !read) begin if (!drop_on_error) next_empty = 1'b0; else if (curr_sop_ptr == rd_ptr) // drop on error and only 1 pkt in fifo next_empty = 1'b1; if (incremented_wr_ptr == rd_ptr && !drop_on_error) next_full = 1'b1; end if (write && read && drop_on_error) begin if (curr_sop_ptr == next_rd_ptr) next_empty = 1'b1; end end always @(posedge clk or posedge reset) begin if (reset) begin empty <= 1; full <= 0; end else begin empty <= next_empty; full <= next_full; end end end else begin : gen_blk13_else // -------------------------------------------------- // Register FIFO Status Management // // Full when the tail occupancy bit is 1. Empty when // the head occupancy bit is 0. // -------------------------------------------------- always @* begin full = mem_used[DEPTH-1]; empty = !mem_used[0]; // ------------------------------------------ // For a single slot FIFO, reading clears the // full status immediately. // ------------------------------------------ if (DEPTH == 1) full = mem_used[0] && !read; internal_out_payload = mem[0]; // ------------------------------------------ // Writes clear empty immediately for lookahead modes. // Note that we use in_valid instead of write to avoid // combinational loops (in lookahead mode, qualifying // with in_ready is meaningless). // // In a 1-deep FIFO, a possible combinational loop runs // from write -> out_valid -> out_ready -> write // ------------------------------------------ if (EMPTY_LATENCY == 0) begin empty = !mem_used[0] && !in_valid; if (!mem_used[0] && in_valid) internal_out_payload = in_payload; end end end endgenerate // -------------------------------------------------- // Avalon-ST Signals // // The in_ready signal is straightforward. // // To match memory latency when empty latency > 1, // out_valid assertions must be delayed by one clock // cycle. // // Note: out_valid deassertions must not be delayed or // the FIFO will underflow. // -------------------------------------------------- assign in_ready = !full; assign internal_out_ready = out_ready || !out_valid; generate if (EMPTY_LATENCY > 1) begin : gen_blk14 always @(posedge clk or posedge reset) begin if (reset) internal_out_valid <= 0; else begin internal_out_valid <= !empty & ok_to_forward & ~drop_on_error; if (read) begin if (incremented_rd_ptr == wr_ptr) internal_out_valid <= 1'b0; end end end end else begin : gen_blk14_else always @* begin internal_out_valid = !empty & ok_to_forward; end end endgenerate // -------------------------------------------------- // Single Output Pipeline Stage // // This output pipeline stage is enabled if the FIFO's // empty latency is set to 3 (default). It is disabled // for all other allowed latencies. // // Reason: The memory outputs are unregistered, so we have to // register the output or fmax will drop if combinatorial // logic is present on the output datapath. // // Q: The Avalon-ST spec says that I have to register my outputs // But isn't the memory counted as a register? // A: The path from the address lookup to the memory output is // slow. Registering the memory outputs is a good idea. // // The registers get packed into the memory by the fitter // which means minimal resources are consumed (the result // is a altsyncram with registered outputs, available on // all modern Altera devices). // // This output stage acts as an extra slot in the FIFO, // and complicates the fill level. // -------------------------------------------------- generate if (EMPTY_LATENCY == 3) begin : gen_blk15 always @(posedge clk or posedge reset) begin if (reset) begin out_valid <= 0; out_payload <= 0; end else begin if (internal_out_ready) begin out_valid <= internal_out_valid & ok_to_forward; out_payload <= internal_out_payload; end end end end else begin : gen_blk15_else always @* begin out_valid = internal_out_valid; out_payload = internal_out_payload; end end endgenerate // -------------------------------------------------- // Fill Level // // The fill level is calculated from the next write // and read pointers to avoid unnecessary latency // and logic. // // However, if the store-and-forward mode of the FIFO // is enabled, the fill level is an up-down counter // for fmax optimization reasons. // // If the output pipeline is enabled, the fill level // must account for it, or we'll always be off by one. // This may, or may not be important depending on the // application. // // For now, we'll always calculate the exact fill level // at the cost of an extra adder when the output stage // is enabled. // -------------------------------------------------- generate if (USE_FILL_LEVEL) begin : gen_blk16 wire [31:0] depth32; assign depth32 = DEPTH; if (USE_STORE_FORWARD) begin reg [ADDR_WIDTH : 0] curr_packet_len_less_one; // -------------------------------------------------- // We only drop on endofpacket. As long as we don't add to the fill // level on the dropped endofpacket cycle, we can simply subtract // (packet length - 1) from the fill level for dropped packets. // -------------------------------------------------- always @(posedge clk or posedge reset) begin if (reset) begin curr_packet_len_less_one <= 0; end else begin if (write) begin curr_packet_len_less_one <= curr_packet_len_less_one + 1'b1; if (in_endofpacket) curr_packet_len_less_one <= 0; end end end always @(posedge clk or posedge reset) begin if (reset) begin fifo_fill_level <= 0; end else if (drop_on_error) begin fifo_fill_level <= fifo_fill_level - curr_packet_len_less_one; if (read) fifo_fill_level <= fifo_fill_level - curr_packet_len_less_one - 1'b1; end else if (write && !read) begin fifo_fill_level <= fifo_fill_level + 1'b1; end else if (read && !write) begin fifo_fill_level <= fifo_fill_level - 1'b1; end end end else begin always @(posedge clk or posedge reset) begin if (reset) fifo_fill_level <= 0; else if (next_full & !drop_on_error) fifo_fill_level <= depth32[ADDR_WIDTH:0]; else begin fifo_fill_level[ADDR_WIDTH] <= 1'b0; fifo_fill_level[ADDR_WIDTH-1 : 0] <= next_wr_ptr - next_rd_ptr; end end end always @* begin fill_level = fifo_fill_level; if (EMPTY_LATENCY == 3) fill_level = fifo_fill_level + {{ADDR_WIDTH{1'b0}}, out_valid}; end end else begin : gen_blk16_else always @* begin fill_level = 0; end end endgenerate generate if (USE_ALMOST_FULL_IF) begin : gen_blk17 assign almost_full_data = (fill_level >= almost_full_threshold); end else assign almost_full_data = 0; endgenerate generate if (USE_ALMOST_EMPTY_IF) begin : gen_blk18 assign almost_empty_data = (fill_level <= almost_empty_threshold); end else assign almost_empty_data = 0; endgenerate // -------------------------------------------------- // Avalon-MM Status & Control Connection Point // // Register map: // // | Addr | RW | 31 - 0 | // | 0 | R | Fill level | // // The registering of this connection point means // that there is a cycle of latency between // reads/writes and the updating of the fill level. // -------------------------------------------------- generate if (USE_STORE_FORWARD) begin : gen_blk19 assign max_fifo_size = FIFO_DEPTH - 1; always @(posedge clk or posedge reset) begin if (reset) begin almost_full_threshold <= max_fifo_size[23 : 0]; almost_empty_threshold <= 0; cut_through_threshold <= 0; drop_on_error_en <= 0; csr_readdata <= 0; pkt_mode <= 1'b1; end else begin if (csr_read) begin csr_readdata <= 32'b0; if (csr_address == 5) csr_readdata <= {31'b0, drop_on_error_en}; else if (csr_address == 4) csr_readdata <= {8'b0, cut_through_threshold}; else if (csr_address == 3) csr_readdata <= {8'b0, almost_empty_threshold}; else if (csr_address == 2) csr_readdata <= {8'b0, almost_full_threshold}; else if (csr_address == 0) csr_readdata <= {{(31 - ADDR_WIDTH){1'b0}}, fill_level}; end else if (csr_write) begin if(csr_address == 3'b101) drop_on_error_en <= csr_writedata[0]; else if(csr_address == 3'b100) begin cut_through_threshold <= csr_writedata[23:0]; pkt_mode <= (csr_writedata[23:0] == 0); end else if(csr_address == 3'b011) almost_empty_threshold <= csr_writedata[23:0]; else if(csr_address == 3'b010) almost_full_threshold <= csr_writedata[23:0]; end end end end else if (USE_ALMOST_FULL_IF || USE_ALMOST_EMPTY_IF) begin : gen_blk19_else1 assign max_fifo_size = FIFO_DEPTH - 1; always @(posedge clk or posedge reset) begin if (reset) begin almost_full_threshold <= max_fifo_size[23 : 0]; almost_empty_threshold <= 0; csr_readdata <= 0; end else begin if (csr_read) begin csr_readdata <= 32'b0; if (csr_address == 3) csr_readdata <= {8'b0, almost_empty_threshold}; else if (csr_address == 2) csr_readdata <= {8'b0, almost_full_threshold}; else if (csr_address == 0) csr_readdata <= {{(31 - ADDR_WIDTH){1'b0}}, fill_level}; end else if (csr_write) begin if(csr_address == 3'b011) almost_empty_threshold <= csr_writedata[23:0]; else if(csr_address == 3'b010) almost_full_threshold <= csr_writedata[23:0]; end end end end else begin : gen_blk19_else2 always @(posedge clk or posedge reset) begin if (reset) begin csr_readdata <= 0; end else if (csr_read) begin csr_readdata <= 0; if (csr_address == 0) csr_readdata <= {{(31 - ADDR_WIDTH){1'b0}}, fill_level}; end end end endgenerate // -------------------------------------------------- // Store and forward logic // -------------------------------------------------- // if the fifo gets full before the entire packet or the // cut-threshold condition is met then start sending out // data in order to avoid dead-lock situation generate if (USE_STORE_FORWARD) begin : gen_blk20 assign wait_for_threshold = (fifo_fill_level_lt_cut_through_threshold) & wait_for_pkt ; assign wait_for_pkt = pkt_cnt_eq_zero | (pkt_cnt_eq_one & out_pkt_leave); assign ok_to_forward = (pkt_mode ? (~wait_for_pkt | ~pkt_has_started) : ~wait_for_threshold) | fifo_too_small_r; assign in_pkt_eop_arrive = in_valid & in_ready & in_endofpacket; assign in_pkt_start = in_valid & in_ready & in_startofpacket; assign in_pkt_error = in_valid & in_ready & |in_error; assign out_pkt_sop_leave = out_valid & out_ready & out_startofpacket; assign out_pkt_leave = out_valid & out_ready & out_endofpacket; assign fifo_too_small = (pkt_mode ? wait_for_pkt : wait_for_threshold) & full & out_ready; // count packets coming and going into the fifo always @(posedge clk or posedge reset) begin if (reset) begin pkt_cnt <= 0; pkt_has_started <= 0; sop_has_left_fifo <= 0; fifo_too_small_r <= 0; pkt_cnt_eq_zero <= 1'b1; pkt_cnt_eq_one <= 1'b0; fifo_fill_level_lt_cut_through_threshold <= 1'b1; end else begin fifo_fill_level_lt_cut_through_threshold <= fifo_fill_level < cut_through_threshold; fifo_too_small_r <= fifo_too_small; if( in_pkt_eop_arrive ) sop_has_left_fifo <= 1'b0; else if (out_pkt_sop_leave & pkt_cnt_eq_zero ) sop_has_left_fifo <= 1'b1; if (in_pkt_eop_arrive & ~out_pkt_leave & ~drop_on_error ) begin pkt_cnt <= pkt_cnt + 1'b1; pkt_cnt_eq_zero <= 0; if (pkt_cnt == 0) pkt_cnt_eq_one <= 1'b1; else pkt_cnt_eq_one <= 1'b0; end else if((~in_pkt_eop_arrive | drop_on_error) & out_pkt_leave) begin pkt_cnt <= pkt_cnt - 1'b1; if (pkt_cnt == 1) pkt_cnt_eq_zero <= 1'b1; else pkt_cnt_eq_zero <= 1'b0; if (pkt_cnt == 2) pkt_cnt_eq_one <= 1'b1; else pkt_cnt_eq_one <= 1'b0; end if (in_pkt_start) pkt_has_started <= 1'b1; else if (in_pkt_eop_arrive) pkt_has_started <= 1'b0; end end // drop on error logic always @(posedge clk or posedge reset) begin if (reset) begin sop_ptr <= 0; error_in_pkt <= 0; end else begin // save the location of the SOP if ( in_pkt_start ) sop_ptr <= wr_ptr; // remember if error in pkt // log error only if packet has already started if (in_pkt_eop_arrive) error_in_pkt <= 1'b0; else if ( in_pkt_error & (pkt_has_started | in_pkt_start)) error_in_pkt <= 1'b1; end end assign drop_on_error = drop_on_error_en & (error_in_pkt | in_pkt_error) & in_pkt_eop_arrive & ~sop_has_left_fifo & ~(out_pkt_sop_leave & pkt_cnt_eq_zero); assign curr_sop_ptr = (write && in_startofpacket && in_endofpacket) ? wr_ptr : sop_ptr; end else begin : gen_blk20_else assign ok_to_forward = 1'b1; assign drop_on_error = 1'b0; if (ADDR_WIDTH <= 1) assign curr_sop_ptr = 1'b0; else assign curr_sop_ptr = {ADDR_WIDTH - 1 { 1'b0 }}; end endgenerate // -------------------------------------------------- // Calculates the log2ceil of the input value // -------------------------------------------------- function integer log2ceil; input integer val; reg[31:0] i; begin i = 1; log2ceil = 0; while (i < val) begin log2ceil = log2ceil + 1; i = i[30:0] << 1; end end endfunction endmodule
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