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

Original-commit: 0df4b801a34697f2058b4a7b95e08d2a0576c9db

lib/fifo/axi_fifo.v

@@ -0,0 +1,169 @@
+//
+// Copyright 2012-2013 Ettus Research LLC
+//
+
+
+
+// Block RAM AXI fifo
+
+// Special case SIZE <= 5 uses a short fifo
+
+module axi_fifo
+  #(parameter WIDTH=32, SIZE=9)
+   (input clk, input reset, input clear,
+    input [WIDTH-1:0] i_tdata,
+    input i_tvalid,
+    output i_tready,
+    output [WIDTH-1:0] o_tdata,
+    output o_tvalid,
+    input o_tready,
+    
+    output reg [15:0] space,
+    output reg [15:0] occupied);
+
+    generate
+    if(SIZE<=5) begin
+        wire [5:0] space_short, occupied_short;
+        axi_fifo_short #(.WIDTH(WIDTH)) fifo_short
+        (
+            .clk(clk), .reset(reset), .clear(clear),
+            .i_tdata(i_tdata), .i_tvalid(i_tvalid), .i_tready(i_tready),
+            .o_tdata(o_tdata), .o_tvalid(o_tvalid), .o_tready(o_tready),
+            .space(space_short), .occupied(occupied_short)
+        );
+        always @* space <= {10'b0, space_short};
+        always @* occupied <= {10'b0, occupied_short};
+    end
+    else begin
+
+   wire 	      write 	     = i_tvalid & i_tready;
+   wire 	      read 	     = o_tvalid & o_tready;
+   wire 	      full, empty;
+   
+   assign i_tready  = ~full;
+   assign o_tvalid  = ~empty;
+   
+   // Read side states
+   localparam 	  EMPTY = 0;
+   localparam 	  PRE_READ = 1;
+   localparam 	  READING = 2;
+
+   reg [SIZE-1:0] wr_addr, rd_addr;
+   reg [1:0] 	  read_state;
+
+   reg 	  empty_reg, full_reg;
+   always @(posedge clk)
+     if(reset)
+       wr_addr <= 0;
+     else if(clear)
+       wr_addr <= 0;
+     else if(write)
+       wr_addr <= wr_addr + 1;
+
+   ram_2port #(.DWIDTH(WIDTH),.AWIDTH(SIZE))
+     ram (.clka(clk),
+	  .ena(1'b1),
+	  .wea(write),
+	  .addra(wr_addr),
+	  .dia(i_tdata),
+	  .doa(),
+
+	  .clkb(clk),
+	  .enb((read_state==PRE_READ)|read),
+	  .web(1'b0),
+	  .addrb(rd_addr),
+	  .dib({WIDTH{1'b1}}),
+	  .dob(o_tdata));
+
+   always @(posedge clk)
+     if(reset)
+       begin
+	  read_state <= EMPTY;
+	  rd_addr <= 0;
+	  empty_reg <= 1;
+       end
+     else
+       if(clear)
+	 begin
+	    read_state <= EMPTY;
+	    rd_addr <= 0;
+	    empty_reg <= 1;
+	 end
+       else 
+	 case(read_state)
+	   EMPTY :
+	     if(write)
+	       begin
+		  //rd_addr <= wr_addr;
+		  read_state <= PRE_READ;
+	       end
+	   PRE_READ :
+	     begin
+		read_state <= READING;
+		empty_reg <= 0;
+		rd_addr <= rd_addr + 1;
+	     end
+	   
+	   READING :
+	     if(read)
+	       if(rd_addr == wr_addr)
+		 begin
+		    empty_reg <= 1; 
+		    if(write)
+		      read_state <= PRE_READ;
+		    else
+		      read_state <= EMPTY;
+		 end
+	       else
+		 rd_addr <= rd_addr + 1;
+	 endcase // case(read_state)
+
+   wire [SIZE-1:0] dont_write_past_me = rd_addr - 2;
+   wire 	   becoming_full = wr_addr == dont_write_past_me;
+     
+   always @(posedge clk)
+     if(reset)
+       full_reg <= 0;
+     else if(clear)
+       full_reg <= 0;
+     else if(read & ~write)
+       full_reg <= 0;
+     //else if(write & ~read & (wr_addr == (rd_addr-3)))
+     else if(write & ~read & becoming_full)
+       full_reg <= 1;
+
+   //assign empty = (read_state != READING);
+   assign empty = empty_reg;
+
+   // assign full = ((rd_addr - 1) == wr_addr);
+   assign full = full_reg;
+
+   //////////////////////////////////////////////
+   // space and occupied are for diagnostics only
+   // not guaranteed exact
+
+   localparam NUMLINES = (1<<SIZE);
+   always @(posedge clk)
+     if(reset)
+       space <= NUMLINES;
+     else if(clear)
+       space <= NUMLINES;
+     else if(read & ~write)
+       space <= space + 16'b1;
+     else if(write & ~read)
+       space <= space - 16'b1;
+   
+   always @(posedge clk)
+     if(reset)
+       occupied <= 16'b0;
+     else if(clear)
+       occupied <= 16'b0;
+     else if(read & ~write)
+       occupied <= occupied - 16'b1;
+     else if(write & ~read)
+       occupied <= occupied + 16'b1;
+
+    end
+    endgenerate
+
+endmodule // fifo_long