Squashed B200 FPGA Source. Code from Josh Blum, Ian Buckley, and Matt Ettus.

Original-commit: 0df4b801a34697f2058b4a7b95e08d2a0576c9db

lib/control/axi_fifo_header.v

@@ -0,0 +1,84 @@
+//
+// Copyright 2012 Ettus Research LLC
+//
+
+
+//
+// This module is connected to the output port of an AXI4-STREAM FIFO that is used to move packetized data.
+// It extracts and indicates the header (first word) of a packet in the FIFO. The header and flag are pipelined
+// for timing closure.
+//
+
+module axi_fifo_header
+  #(
+    parameter WIDTH=64  // Bit width of FIFO word.
+    )
+    (
+     input clk,
+     input reset,
+     input clear,
+     // Monitored FIFO signals
+     input [WIDTH-1:0] o_tdata,
+     input o_tvalid,
+     input o_tready,
+     input o_tlast,
+     input pkt_present,
+     // Header signals
+     output reg [WIDTH-1:0] header,
+     output reg header_valid
+     );
+
+   localparam WAIT_SOF = 0;
+   localparam WAIT_EOF = 1;
+   
+   reg 	    out_state;
+   
+
+    //
+    // Monitor packets leaving FIFO
+    //
+    always @(posedge clk)
+      if (reset | clear) begin
+         out_state <= WAIT_SOF;
+      end else
+	case(out_state)
+	  //
+	  // After RESET or the EOF of previous packet, the first cycle with
+	  // output valid asserted is the SOF and presents the Header word.
+	  // The cycle following the concurrent presentation of asserted output 
+	  // valid and output ready presents the word following the header.
+	  //
+          WAIT_SOF: 
+            if (o_tvalid && o_tready) begin
+               out_state <= WAIT_EOF;
+            end else begin
+               out_state <= WAIT_SOF;
+            end
+	  //
+	  // EOF is signalled by o_tlast asserted whilst output valid and ready asserted.
+	  //
+          WAIT_EOF: 
+            if (o_tlast && o_tvalid && o_tready) begin
+               out_state <= WAIT_SOF;
+            end else begin
+               out_state <= WAIT_EOF;
+            end
+	endcase // case(in_state)
+   
+   //
+   // Pipeline Header signals
+   //
+   always @(posedge clk)
+     if (reset | clear) begin
+	header <= 0;
+	header_valid <= 0;
+     end else if (o_tvalid && (out_state == WAIT_SOF) && pkt_present) begin
+	// Header will remian valid until o_tready is asserted as this will cause a state transition.
+	header <= o_tdata;
+	header_valid <= 1;
+     end else begin
+	header_valid <= 0;
+     end
+
+
+endmodule // axi_fifo_header