1 files changed, 87 insertions, 0 deletions
diff --git a/fpga/usrp2/control_lib/shortfifo.v b/fpga/usrp2/control_lib/shortfifo.v
new file mode 100644
index 000000000..d8ce1428e
--- /dev/null
+++ b/fpga/usrp2/control_lib/shortfifo.v
@@ -0,0 +1,87 @@
+
+module shortfifo
+  #(parameter WIDTH=32)
+    (input clk, input rst,
+     input [WIDTH-1:0] datain,
+     output [WIDTH-1:0] dataout,
+     input read,
+     input write,
+     input clear,
+     output reg full,
+     output reg empty,
+     output reg [4:0] space,
+     output reg [4:0] occupied);
+   
+   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(rst)
+       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(rst)
+       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(rst)
+       occupied <= 0;
+     else if(clear)
+       occupied <= 0;
+     else if(read & ~write)
+       occupied <= occupied - 1;
+     else if(write & ~read)
+       occupied <= occupied + 1;
+      
+endmodule // shortfifo