import Vivado project, rearrange Verilog sources

tridoracpu/tridoracpu.srcs/sfifo.v

@@ -0,0 +1,84 @@
+`timescale 1ns / 1ps
+
+// a simple fifo
+module fifo #(parameter DATA_WIDTH = 8, ADDR_WIDTH = 4)(
+    input wire clk,
+    input wire reset,
+    input wire wr_en,
+    input wire rd_en,
+    input wire [DATA_WIDTH-1:0] wr_data,
+    output wire [DATA_WIDTH-1:0] rd_data,
+    output wire wr_full,
+    output wire rd_empty
+    );
+
+    reg [DATA_WIDTH-1:0] mem [0:ADDR_WIDTH-1];
+    reg [ADDR_WIDTH:0]  head_x = 0;  // head and tail have one extra bit 
+    reg [ADDR_WIDTH:0]  tail_x = 0;  // for detecting overflows
+    wire [ADDR_WIDTH-1:0] head = head_x[ADDR_WIDTH-1:0];
+    wire [ADDR_WIDTH-1:0] tail = tail_x[ADDR_WIDTH-1:0];
+    
+    assign rd_data = mem[tail];
+    // the fifo is full when head and tail pointer are the same
+    // and the extra bits differ (a wraparound occured)
+    assign wr_full = (head == tail) && (head_x[ADDR_WIDTH] != tail_x[ADDR_WIDTH]);
+    // the fifo is empty when head and tail pointer are the same
+    // and the extra bits are the same (no wraparound)
+    assign rd_empty = (head == tail) && (head_x[ADDR_WIDTH] == tail_x[ADDR_WIDTH]);
+  
+    // Writing to FIFO
+    always @(posedge clk) begin
+        if (wr_en)
+        begin
+            mem[head[ADDR_WIDTH-1:0]] <= wr_data;
+            // move head, possible wraparound
+            head_x <= head_x + 1'b1;
+        end
+    end
+
+    // Reading from FIFO
+    always @(posedge clk)
+    begin
+        if (rd_en)
+        begin
+            // rd_data always has current tail data
+            // move tail, possible wraparound
+            tail <= tail + 1'b1;
+        end
+    end
+
+    // Calculating full/empty flags, referenced from zipcpu.com
+    wire	[c_DEPTH:0]	dblnext, nxtread;
+    assign	dblnext = wraddr + 2;
+    assign	nxtread = rdaddr + 1'b1;
+
+    always @(posedge i_Clock, negedge i_Reset)
+    
+        // Reset case
+        if (!i_Reset)
+        begin
+            // Reset output flags
+            fifo_full <= 1'b0;
+            fifo_empty <= 1'b1;
+            
+        end else casez({ i_Write_En, i_Read_En, !fifo_full, !fifo_empty })
+        4'b01?1: begin	// A successful read
+            fifo_full  <= 1'b0;
+            fifo_empty <= (nxtread == wraddr);
+        end
+        4'b101?: begin	// A successful write
+            fifo_full <= (dblnext == rdaddr);
+            fifo_empty <= 1'b0;
+        end
+        4'b11?0: begin	// Successful write, failed read
+            fifo_full  <= 1'b0;
+            fifo_empty <= 1'b0;
+        end
+        4'b11?1: begin	// Successful read and write
+            fifo_full  <= fifo_full;
+            fifo_empty <= 1'b0;
+        end
+        default: begin end
+        endcase
+    
+endmodule