--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cp2102/read_partno.c	Mon Sep 11 17:41:24 2023 +0000
@@ -0,0 +1,51 @@
+/*
+ * This program locates a presumed-CP2102 device via libusb and reads its
+ * vendor-specific part number register, seeking to distinguish between
+ * the original CP2102 and the later CP2102N.
+ */
+
+#include <sys/types.h>
+#include <string.h>
+#include <strings.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <usb.h>
+#include "../libuwrap/find_dev.h"
+#include "cp210x_defs.h"
+
+main(argc, argv)
+	char **argv;
+{
+	struct usb_device *dev;
+	usb_dev_handle *usbh;
+	u_char partno;
+	int rc;
+
+	if (argc != 2) {
+		fprintf(stderr, "usage: %s device-selector\n", argv[0]);
+		exit(1);
+	}
+	dev = find_usbdev_by_desc_string(argv[1]);
+	if (!dev) {
+		fprintf(stderr, "error: specified USB device not found\n");
+		exit(1);
+	}
+	usbh = usb_open(dev);
+	if (!usbh) {
+		fprintf(stderr, "error: usb_open() failed\n");
+		exit(1);
+	}
+	rc = usb_control_msg(usbh, DEVICE_IN_REQTYPE, CP210x_CONFIG, 0,
+			     REG_PART_NUMBER, (char *) &partno, 1,
+			     USB_READ_TIMEOUT);
+	if (rc != 1) {
+		fprintf(stderr,
+		"REG_PART_NUMBER read error: usb_control_msg() returned %d\n",
+			rc);
+		exit(1);
+	}
+	usb_close(usbh);
+	printf("0x%02X\n", partno);
+	exit(0);
+}