1 files changed, 95 insertions, 0 deletions
diff --git a/fpga/usrp2/fifo/fifo_short.v b/fpga/usrp2/fifo/fifo_short.v
new file mode 100644
index 000000000..53a7603c7
--- /dev/null
+++ b/fpga/usrp2/fifo/fifo_short.v
@@ -0,0 +1,95 @@
+
+module fifo_short
+  #(parameter WIDTH=32)
+   (input clk, input reset, input clear,
+    input [WIDTH-1:0] datain,
+    input src_rdy_i,
+    output dst_rdy_o,
+    output [WIDTH-1:0] dataout,
+    output src_rdy_o,
+    input dst_rdy_i,
+    
+    output reg [4:0] space,
+    output reg [4:0] occupied);
+
+   reg full, empty;
+   wire write 	     = src_rdy_i & dst_rdy_o;
+   wire read 	     = dst_rdy_i & src_rdy_o;
+
+   assign dst_rdy_o  = ~full;
+   assign src_rdy_o  = ~empty;
+   
+   reg [3:0] 	  a;
+   genvar 	  i;
+   
+   generate
+      for (i=0;i<WIDTH;i=i+1)
+	begin : gen_srl16
+	   SRL16E
+	     srl16e(.Q(dataout[i]),
+		    .A0(a[0]),.A1(a[1]),.A2(a[2]),.A3(a[3]),
+		    .CE(write),.CLK(clk),.D(datain[i]));
+	end
+   endgenerate
+   
+   always @(posedge clk)
+     if(reset)
+       begin
+	  a <= 0;
+	  empty <= 1;
+	  full <= 0;
+       end
+     else if(clear)
+       begin
+	  a <= 0;
+	  empty <= 1;
+	  full<= 0;
+       end
+     else if(read & ~write)
+       begin
+	  full <= 0;
+	  if(a==0)
+	    empty <= 1;
+	  else
+	    a <= a - 1;
+       end
+     else if(write & ~read)
+       begin
+	  empty <= 0;
+	  if(~empty)
+	    a <= a + 1;
+	  if(a == 14)
+	    full <= 1;
+       end
+
+   // NOTE will fail if you write into a full fifo or read from an empty one
+
+   //////////////////////////////////////////////////////////////
+   // space and occupied are used for diagnostics, not 
+   // guaranteed correct
+   
+   //assign space = full ? 0 : empty ? 16 : 15-a;
+   //assign occupied = empty ? 0 : full ? 16 : a+1;
+
+   always @(posedge clk)
+     if(reset)
+       space <= 16;
+     else if(clear)
+       space <= 16;
+     else if(read & ~write)
+       space <= space + 1;
+     else if(write & ~read)
+       space <= space - 1;
+   
+   always @(posedge clk)
+     if(reset)
+       occupied <= 0;
+     else if(clear)
+       occupied <= 0;
+     else if(read & ~write)
+       occupied <= occupied - 1;
+     else if(write & ~read)
+       occupied <= occupied + 1;
+      
+endmodule // fifo_short
+