1 files changed, 66 insertions, 0 deletions
diff --git a/control_lib/fifo_2clock.v b/control_lib/fifo_2clock.v
new file mode 100644
index 000000000..6b1eb607e
--- /dev/null
+++ b/control_lib/fifo_2clock.v
@@ -0,0 +1,66 @@
+
+module fifo_2clock
+  #(parameter DWIDTH=32, AWIDTH=9)
+    (input wclk, input [DWIDTH-1:0] datain, input write, output full, output reg [AWIDTH-1:0] level_wclk,
+     input rclk, output [DWIDTH-1:0] dataout, input read, output empty, output reg [AWIDTH-1:0] level_rclk,
+     input arst);
+
+   reg [AWIDTH-1:0] wr_addr, rd_addr;
+   wire [AWIDTH-1:0] wr_addr_rclk, rd_addr_wclk;
+   wire [AWIDTH-1:0] next_rd_addr;
+   wire 	    enb_read;
+   
+   // Write side management
+   wire [AWIDTH-1:0] next_wr_addr = wr_addr + 1;
+   always @(posedge wclk or posedge arst)
+     if(arst)
+       wr_addr <= 0;
+     else if(write)
+       wr_addr <= next_wr_addr;
+   assign 	    full = (next_wr_addr == rd_addr_wclk);
+
+   //  RAM for data storage.  Data out is registered, complicating the
+   //     read side logic
+   ram_2port #(.DWIDTH(DWIDTH),.AWIDTH(AWIDTH)) mac_rx_ff_ram
+     (.clka(wclk),.ena(1'b1),.wea(write),.addra(wr_addr),.dia(datain),.doa(),
+      .clkb(rclk),.enb(enb_read),.web(1'b0),.addrb(next_rd_addr),.dib(0),.dob(dataout) );
+
+   // Read side management
+   reg 		    data_valid;
+   assign 	    empty = ~data_valid;
+   assign 	    next_rd_addr = rd_addr + data_valid;
+   assign 	    enb_read = read | ~data_valid;
+
+   always @(posedge rclk or posedge arst)
+     if(arst)
+       rd_addr <= 0;
+     else if(read)
+       rd_addr <= rd_addr + 1;
+
+   always @(posedge rclk or posedge arst)
+     if(arst)
+       data_valid <= 0;
+     else
+       if(read & (next_rd_addr == wr_addr_rclk))
+	 data_valid <= 0;
+       else if(next_rd_addr != wr_addr_rclk)
+	 data_valid <= 1;
+	 
+   // Send pointers across clock domains via gray code
+   gray_send #(.WIDTH(AWIDTH)) send_wr_addr
+     (.clk_in(wclk),.addr_in(wr_addr),
+      .clk_out(rclk),.addr_out(wr_addr_rclk) );
+   
+   gray_send #(.WIDTH(AWIDTH)) send_rd_addr
+     (.clk_in(rclk),.addr_in(rd_addr),
+      .clk_out(wclk),.addr_out(rd_addr_wclk) );
+
+   // Generate fullness info, these are approximate and may be delayed 
+   // and are only for higher-level flow control.  
+   // Only full and empty are guaranteed exact.
+   always @(posedge wclk) 
+     level_wclk <= wr_addr - rd_addr_wclk;
+   always @(posedge rclk) 
+     level_rclk <= wr_addr_rclk - rd_addr;
+   
+endmodule // fifo_2clock