Fixed video, kbd and buzzer

cpu/toplevel/tb_io.sv

@@ -0,0 +1,61 @@
+//--------------------------------------------------------------
+// Implements I/O Model for simulation
+//--------------------------------------------------------------
+module io (Address, Data, CS, WE, OE);
+
+// Set to 1 to have text output to the file "iolog.txt"
+int iolog = 1;
+
+// Set to 1 if you want debug printout on each IO access
+int debug = 0;
+
+int fd;
+input [15:0] Address;
+inout [7:0] Data;
+input CS, WE, OE;
+
+reg [7:0] IO [0:1<<16];
+
+// Return data for the specified IO address:
+//  1. If the current address is 0A00, that's the UART busy bit (which is never busy for ModelSim), so return 00
+//  2. If the IO map is not defined for the current address, return FF
+//  3. If the IO map is defined, return the value from it
+//  4. Lastly, if !CS and !OE (not selecting the IO), tri-state the data bus
+assign Data = (!CS && !OE) ? (Address==16'h0A00)? 8'h00 : (IO[Address]===8'hxx) ? 8'hFF : IO[Address] : {8{1'bz}};
+
+// Read the initial content of the IO map from file
+initial begin : init
+    $readmemh("io.hex", IO);
+    // If logging to a file was enabled, clear the file so we can append
+    if (iolog) begin
+        fd = $fopen("iolog.txt", "wb");
+        $fclose(fd);
+    end
+end : init
+
+always @(!CS && !OE) begin
+    if (debug)
+        $strobe("[IO] IN A=%H, D=%H", Address, Data);
+end
+
+always @(CS or WE)
+    if (!CS && !WE) begin
+        if (debug)
+            $strobe("[IO] OUT A=%H, D=%H", Address, Data);
+        if (Address==8*256) begin
+            $write("%c", Data);
+            // If logging to a file was enabled, append a character
+            if (iolog) begin
+                fd = $fopen("iolog.txt", "ab");
+                $fwrite(fd, "%c", Data);
+                $fclose(fd);
+            end
+        end
+        IO[Address] = Data;
+    end
+
+always @(WE or OE)
+    if (!WE && !OE)
+        $display("[IO] error: OE and WE both active!");
+
+endmodule