Allow port routing to be canceled. It is needed for serial ports.

cmd.c

 			break;
 		case PARSE_ROUTE:
 			dest_port_num = strtoul(port_data, NULL, 10);
+			if (dest_port_num == NO_PORT) {
+				// Only serial port routing can be disabled with -1
+				if (v->cmd == CMD_SERIAL_PORT_ROUTING) {
+					s_port->port[port_num].routed_to = dest_port_num;
+					continue;
+				} else {
+					dest_port_num = port_num;
+				}
+			}
 			if (dest_port_num + 1 > d_port->num) {
 				q("WARNING: %s: invalid %s port %u (valid 0..%u)\n", cmd_txt,
 				  v->port_id2, dest_port_num, d_port->num - 1);
 				continue;
 			}
 			s_port->port[port_num].routed_to = dest_port_num;
-			s_port->port[port_num].routed_to_set = true;
 			break;
 		case PARSE_LOCK:
 			switch (port_data[0]) {

data.h

 #define MAX_PORTS 288
 #define MAX_NAME_LEN 32
 #define MAX_RUN_CMDS (288 * 5)
+#define NO_PORT ((unsigned int) -1)
 
 struct device_desc {
 	bool			dev_present;
 	//       auto - Automatic
 	enum serial_dir	direction;
 	unsigned int	routed_to;
-	bool			routed_to_set; // For serial ports
 	enum port_lock	lock;
 };
 

display.c

 		if (num_outputs == 0) {
 			printf("%-24s | %c |\n", "-", format_status(d->inputs.port[i].status));
 		} else {
-			printf("%-24s | %c |\n", d->outputs.port[routed_to].name, format_status(d->inputs.port[i].status));
+			printf("%-24s | %c |\n",
+				routed_to == NO_PORT ? "" : d->outputs.port[routed_to].name,
+				format_status(d->inputs.port[i].status)
+			);
 			bool first_skipped = false;
 			for(r = 0; r < d->outputs.num; r++) {
 				if (d->outputs.port[r].routed_to == i) {
 			i + 1,
 			port_lock_symbol(d->outputs.port[i].lock),
 			d->outputs.port[i].name,
-			d->inputs.port[d->outputs.port[i].routed_to].name,
+			d->outputs.port[i].routed_to == NO_PORT ? "" : d->inputs.port[d->outputs.port[i].routed_to].name,
 			format_status(d->outputs.port[i].status)
 		);
 	}
 			i + 1,
 			port_lock_symbol(d->mon_outputs.port[i].lock),
 			d->mon_outputs.port[i].name,
-			d->inputs.port[d->mon_outputs.port[i].routed_to].name
+			d->mon_outputs.port[i].routed_to == NO_PORT ? "" : d->inputs.port[d->mon_outputs.port[i].routed_to].name
 		);
 	}
 	printf_line(len);
 }
 
 void print_device_serial_ports(struct videohub_data *d) {
-	unsigned char port_seen[MAX_PORTS];
 	unsigned int i, len = 63;
 	if (!d->serial.num)
 		return;
-	memset(port_seen, 0, sizeof(port_seen));
 	printf("Serial ports\n");
 	printf_line(len);
 	printf("  | ## | x | Dir  | %-18s | %-18s | s |\n", "Serial port", "Connected serial");
 			port_lock_symbol(d->serial.port[i].lock),
 			dir2opt(d->serial.port[i].direction),
 			d->serial.port[i].name,
-			(d->serial.port[i].routed_to_set && !port_seen[d->serial.port[i].routed_to]
-				? d->serial.port[d->serial.port[i].routed_to].name
-				: ""),
+			d->serial.port[i].routed_to == NO_PORT ? "" : d->serial.port[d->serial.port[i].routed_to].name,
 			format_status(d->serial.port[i].status)
 		);
-		port_seen[d->serial.port[i].routed_to]++;
 	}
 	printf_line(len);
 	printf("\n");
 			printf("  --%s-name %2d \"%s\" \\\n", p, i + 1, s_port->port[i].name);
 			break;
 		case PARSE_ROUTE:
-			if (v->cmd == CMD_SERIAL_PORT_ROUTING && !s_port->port[i].routed_to_set)
+			if (s_port->port[i].routed_to == NO_PORT)
 				continue;
 			printf("  --%s-input %2d %2d \\\n", p, i + 1, s_port->port[i].routed_to + 1);
 			break;

test/input-00.txt

 SERIAL PORT ROUTING:
 0 2
 1 3
+2 5
+3 -1
+2 -1
 
 SERIAL PORT LOCKS:
 0 O
 5 auto
 6 control
 7 slave
+

test/input-14.txt

 10 10
 11 12
 12 11
-13 13
-14 14
+13 -1
+14 -1
 15 15
 

videohubctrl.c

 			p->num, ARRAY_SIZE(p->port));
 }
 
+static void reset_routed_to(struct port_set *p) {
+	unsigned int i;
+	for (i = 0; i < ARRAY_SIZE(p->port); i++)
+		p->port[i].routed_to = NO_PORT;
+}
+
 static void print_device_full(struct videohub_data *d) {
 	print_device_info(d);
 	print_device_video_inputs(d);
 			exit(EXIT_FAILURE);
 	}
 
+	reset_routed_to(&data->serial);
 	read_device_command_stream(data);
 
 	if (test_data)