--- a/cp2102/read_eeprom_main.c	Thu Sep 28 03:26:11 2023 +0000
+++ b/cp2102/read_eeprom_main.c	Thu Sep 28 04:45:13 2023 +0000
@@ -18,6 +18,32 @@
 extern struct usb_device *find_cp2102_device();
 
 u_char eeprom[SIZE_EEPROM];
+char *device_selector, *outfilename;
+
+process_cmdline(argc, argv)
+	char **argv;
+{
+	int c;
+	extern int optind;
+	extern char *optarg;
+
+	while ((c = getopt(argc, argv, "d:")) != EOF) {
+		switch (c) {
+		case 'd':
+			device_selector = optarg;
+			continue;
+		default:
+		usage:
+			fprintf(stderr,
+			"usage: %s [-d device-selector] output-hex-file\n",
+				argv[0]);
+			exit(1);
+		}
+	}
+	if (argc != optind + 1)
+		goto usage;
+	outfilename = argv[optind];
+}
 
 main(argc, argv)
 	char **argv;
@@ -26,12 +52,8 @@
 	usb_dev_handle *usbh;
 	FILE *outf;
 
-	if (argc != 3) {
-		fprintf(stderr, "usage: %s device-selector output-hex-file\n",
-			argv[0]);
-		exit(1);
-	}
-	dev = find_cp2102_device(argv[1]);
+	process_cmdline(argc, argv);
+	dev = find_cp2102_device(device_selector);
 	usbh = usb_open(dev);
 	if (!usbh) {
 		fprintf(stderr, "error: usb_open() failed\n");
@@ -39,9 +61,9 @@
 	}
 	read_eeprom(usbh);
 	usb_close(usbh);
-	outf = fopen(argv[2], "w");
+	outf = fopen(outfilename, "w");
 	if (!outf) {
-		perror(argv[2]);
+		perror(outfilename);
 		exit(1);
 	}
 	intel_hex_out(eeprom, outf);