From 02426607171a1a49b51eef4df45a32cb34a35ff0 Mon Sep 17 00:00:00 2001
From: harbaum <till@harbaum.org>
Date: Fri, 2 May 2014 12:35:13 +0000
Subject: [PATCH] Restoring accidentally deleted file

---
 cores/mist/io_fifo.v | 93 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 93 insertions(+)
 create mode 100644 cores/mist/io_fifo.v

diff --git a/cores/mist/io_fifo.v b/cores/mist/io_fifo.v
new file mode 100644
index 0000000..a3dbc45
--- /dev/null
+++ b/cores/mist/io_fifo.v
@@ -0,0 +1,93 @@
+//
+// io_fifo.v
+// 
+// Atari ST(E) io controller FIFO for the MiST board
+// http://code.google.com/p/mist-board/
+// 
+// Copyright (c) 2013 Till Harbaum <till@harbaum.org> 
+// Modified by Juan Carlos González Amestoy.
+// 
+// This source file is free software: you can redistribute it and/or modify 
+// it under the terms of the GNU General Public License as published 
+// by the Free Software Foundation, either version 3 of the License, or 
+// (at your option) any later version. 
+// 
+// This source file is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of 
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
+// GNU General Public License for more details.
+// 
+// You should have received a copy of the GNU General Public License 
+// along with this program.  If not, see <http://www.gnu.org/licenses/>. 
+
+module io_fifo #(
+ parameter DATA_WIDTH = 8,
+ parameter DEPTH = 4
+)(
+	input reset,
+	
+	input [DATA_WIDTH-1:0] in,
+	input in_clk,
+	input in_strobe,
+	input in_enable,
+	
+	input out_clk,
+	output [DATA_WIDTH-1:0] out,
+	input out_strobe,
+	input out_enable,
+
+	output empty,
+	output data_available,
+	output full
+);
+
+localparam FIFO_ADDR_BITS = DEPTH;
+localparam FIFO_DEPTH = (1 << FIFO_ADDR_BITS);
+
+reg [DATA_WIDTH-1:0] fifo [FIFO_DEPTH-1:0];
+reg [FIFO_ADDR_BITS-1:0] writeP, readP;
+
+assign full = (readP == (writeP + 1));
+assign empty = (readP == writeP);
+assign data_available = (readP != writeP);
+
+// the strobes may not be in the right clock domain, so bring them into the 
+// local clock domain
+reg in_strobeD, in_strobeD2;
+reg out_strobeD, out_strobeD2;
+
+// present current value. If fifo is empty show last value
+assign out = data_available?fifo[readP]:fifo[readP-1];
+
+always @(posedge out_clk) begin
+	// bring strobes in local clock domain
+	out_strobeD <= out_strobe;
+	out_strobeD2 <= out_strobeD;
+	
+	if(reset)
+		readP <= 0;
+	else begin
+		// rising edge on fifo read strobe from io controller
+		if((out_strobeD && !out_strobeD2) || out_enable)
+			readP <= readP + 1;
+	end
+end
+
+always @(posedge in_clk) begin
+	// bring strobes in local clock domain
+	in_strobeD <= in_strobe;
+	in_strobeD2 <= in_strobeD;
+	
+	if(reset)
+		writeP <= 0;
+	else begin
+		// rising edge on strobe signal causes write
+		// or in_enable being true
+		if((in_strobeD && !in_strobeD2) || in_enable) begin
+			fifo[writeP] <= in;
+			writeP <= writeP + 1;
+		end
+	end
+end	
+
+endmodule
\ No newline at end of file