From 7bf8a6df381a667134b55701993c6770d32bc76b Mon Sep 17 00:00:00 2001
From: Josh Blum <josh@joshknows.com>
Date: Fri, 22 Jan 2010 11:56:55 -0800
Subject: Moved usrp2 fpga files into usrp2 subdir.

---
 usrp2/control_lib/longfifo.v | 150 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 150 insertions(+)
 create mode 100644 usrp2/control_lib/longfifo.v

(limited to 'usrp2/control_lib/longfifo.v')

diff --git a/usrp2/control_lib/longfifo.v b/usrp2/control_lib/longfifo.v
new file mode 100644
index 000000000..bf3338e0b
--- /dev/null
+++ b/usrp2/control_lib/longfifo.v
@@ -0,0 +1,150 @@
+
+// FIFO intended to be interchangeable with shortfifo, but
+//  based on block ram instead of SRL16's
+//  only one clock domain
+
+// Port A is write port, Port B is read port
+
+module longfifo
+  #(parameter WIDTH=32, SIZE=9)
+    (input clk, input rst,
+     input [WIDTH-1:0] datain,
+     output [WIDTH-1:0] dataout,
+     input read,
+     input write,
+     input clear,
+     output full,
+     output empty,
+     output reg [15:0] space,
+     output reg [15:0] occupied);
+
+   // 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(rst)
+       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(datain),
+	  .doa(),
+
+	  .clkb(clk),
+	  .enb((read_state==PRE_READ)|read),
+	  .web(0),
+	  .addrb(rd_addr),
+	  .dib(0),
+	  .dob(dataout));
+
+   always @(posedge clk)
+     if(rst)
+       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 - 3;
+   wire 	   becoming_full = wr_addr == dont_write_past_me;
+     
+   always @(posedge clk)
+     if(rst)
+       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)-2;
+   always @(posedge clk)
+     if(rst)
+       space <= NUMLINES;
+     else if(clear)
+       space <= NUMLINES;
+     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;
+   
+   /*
+   wire [SIZE-1:0] fullness = wr_addr - rd_addr;  // Approximate, for simulation only
+   assign occupied = {{16-SIZE{1'b0}},fullness};
+
+   wire [SIZE-1:0] free_space = rd_addr - wr_addr - 2;  // Approximate, for SERDES flow control
+   assign space = {{16-SIZE{1'b0}},free_space};
+    */  
+
+   
+endmodule // longfifo
-- 
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