--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/duart28/find_usb.c	Sat Sep 09 17:53:21 2023 +0000
@@ -0,0 +1,84 @@
+/*
+ * This module implements the step of locating a connected FreeCalypso DUART28
+ * device (either C or S) at the libusb level, without booting off the kernel
+ * driver and claiming the interface yet.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <strings.h>
+#include <usb.h>
+#include "../libuwrap/prelim_init.h"
+
+static void
+get_string(usb_dev_handle *usbh, int index, char *buf, size_t buflen)
+{
+	int rc;
+
+	rc = usb_get_string_simple(usbh, index, buf, buflen);
+	if (rc <= 0) {
+		fprintf(stderr, "error: USB string retrieval failed\n");
+		exit(1);
+	}
+}
+
+static void
+report_found_dev(struct usb_device *dev, unsigned usb_pid, char string_letter)
+{
+	printf("Found FreeCalypso DUART28 adapter at bus %s device %s,\n",
+		dev->bus->dirname, dev->filename);
+	if (usb_pid == 0x7152 && string_letter == 'C')
+		printf("presenting as DUART28C\n");
+	else if (usb_pid == 0x6010 && string_letter == 'S')
+		printf("presenting as DUART28S\n");
+	else
+		printf("presenting with inconsistent ID!\n");
+}
+
+static int
+is_match(struct usb_device *dev)
+{
+	struct usb_device_descriptor *desc = &dev->descriptor;
+	usb_dev_handle *usbh;
+	char strbuf[1024];
+
+	if (desc->idVendor != 0x0403)
+		return 0;
+	if (desc->idProduct != 0x6010 && desc->idProduct != 0x7152)
+		return 0;
+	usbh = usb_open(dev);
+	if (!usbh) {
+		fprintf(stderr, "error: usb_open() failed\n");
+		exit(1);
+	}
+	get_string(usbh, desc->iManufacturer, strbuf, sizeof strbuf);
+	if (strcmp(strbuf, "FreeCalypso")) {
+		usb_close(usbh);
+		return 0;
+	}
+	get_string(usbh, desc->iProduct, strbuf, sizeof strbuf);
+	if (strcmp(strbuf, "DUART28C") && strcmp(strbuf, "DUART28S")) {
+		usb_close(usbh);
+		return 0;
+	}
+	usb_close(usbh);
+	report_found_dev(dev, desc->idProduct, strbuf[7]);
+	return 1;
+}
+
+struct usb_device *
+find_duart28_usbdev()
+{
+	struct usb_bus *bus;
+	struct usb_device *dev;
+
+	libusb_prelim_init();
+	for (bus = usb_get_busses(); bus; bus = bus->next) {
+		for (dev = bus->devices; dev; dev = dev->next) {
+			if (is_match(dev))
+				return dev;
+		}
+	}
+	return 0;
+}