diff --git a/atusb/fw/descr.c b/atusb/fw/descr.c
index 147e180..56447ff 100644
--- a/atusb/fw/descr.c
+++ b/atusb/fw/descr.c
@@ -1,8 +1,8 @@
 /*
  * fw/descr.c - USB descriptors
  *
- * Written 2008-2011 by Werner Almesberger
- * Copyright 2008-2011 Werner Almesberger
+ * Written 2008-2011, 2014 by Werner Almesberger
+ * Copyright 2008-2011, 2014 Werner Almesberger
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -100,5 +100,5 @@ const uint8_t config_descriptor[] = {
 
 	/* Interface #1 */
 
-	DFU_ITF_DESCR(1, dfu_proto_runtime)
+	DFU_ITF_DESCR(1, 0, dfu_proto_runtime)
 };
diff --git a/atusb/fw/flash.c b/atusb/fw/flash.c
index 54d9a19..75b5782 100644
--- a/atusb/fw/flash.c
+++ b/atusb/fw/flash.c
@@ -1,8 +1,8 @@
 /*
  * fw/flash.c - Board-specific flash functions
  *
- * Written 2011, 2013 by Werner Almesberger
- * Copyright 2011, 2013 Werner Almesberger
+ * Written 2011, 2013, 2014 by Werner Almesberger
+ * Copyright 2011, 2013, 2014 Werner Almesberger
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -24,19 +24,19 @@
 static uint32_t payload;
 
 
-void flash_start(void)
+static void flash_start(void)
 {
 	payload = 0;
 }
 
 
-bool flash_can_write(uint16_t size)
+static bool flash_can_write(uint16_t size)
 {
 	return payload+size <= BOOT_ADDR;
 }
 
 
-void flash_write(const uint8_t *buf, uint16_t size)
+static void flash_write(const uint8_t *buf, uint16_t size)
 {
 	static uint8_t last;
         const uint8_t *p;
@@ -61,7 +61,7 @@ void flash_write(const uint8_t *buf, uint16_t size)
 }
 
 
-void flash_end_write(void)
+static void flash_end_write(void)
 {
 	if (payload & (SPM_PAGESIZE-1)) {
 		boot_page_write(payload & ~(SPM_PAGESIZE-1));
@@ -71,7 +71,7 @@ void flash_end_write(void)
 }
 
 
-uint16_t flash_read(uint8_t *buf, uint16_t size)
+static uint16_t flash_read(uint8_t *buf, uint16_t size)
 {
 	uint16_t got = 0;
 
@@ -83,3 +83,15 @@ uint16_t flash_read(uint8_t *buf, uint16_t size)
 	}
 	return got;
 }
+
+
+static struct dfu_flash_ops flash_ops = {
+	.start		= flash_start,
+	.can_write	= flash_can_write,
+	.write		= flash_write,
+	.end_write	= flash_end_write,
+	.read		= flash_read,
+};
+
+
+struct dfu_flash_ops *dfu_flash_ops = &flash_ops;
diff --git a/atusb/fw/usb/dfu.c b/atusb/fw/usb/dfu.c
index dc8bab3..723221c 100644
--- a/atusb/fw/usb/dfu.c
+++ b/atusb/fw/usb/dfu.c
@@ -42,6 +42,11 @@
 #define error(...)
 
 
+#ifndef DFU_ALT_SETTINGS
+#define	DFU_ALT_SETTINGS	1
+#endif
+
+
 const uint8_t device_descriptor[] = {
 	18,			/* bLength */
 	USB_DT_DEVICE,		/* bDescriptorType */
@@ -67,7 +72,7 @@ const uint8_t device_descriptor[] = {
 const uint8_t config_descriptor[] = {
 	9,			/* bLength */
 	USB_DT_CONFIG,		/* bDescriptorType */
-	LE(9+9),		/* wTotalLength */
+	LE(9+9*DFU_ALT_SETTINGS), /* wTotalLength */
 	1,			/* bNumInterfaces */
 	1,			/* bConfigurationValue (> 0 !) */
 	0,			/* iConfiguration */
@@ -77,7 +82,13 @@ const uint8_t config_descriptor[] = {
 
 	/* Interface #0 */
 
-	DFU_ITF_DESCR(0, dfu_proto_dfu)
+	DFU_ITF_DESCR(0, 0, dfu_proto_dfu)
+#if DFU_ALT_SETTINGS >= 1
+	DFU_ITF_DESCR(0, 1, dfu_proto_dfu)
+#endif
+#if DFU_ALT_SETTINGS >= 2
+	DFU_ITF_DESCR(0, 2, dfu_proto_dfu)
+#endif
 };
 
 
@@ -92,7 +103,7 @@ static void block_write(void *user)
 {
 	uint16_t *size = user;
 
-	flash_write(buf, *size);
+	dfu_flash_ops->write(buf, *size);
 }
 
 
@@ -100,7 +111,7 @@ static bool block_receive(uint16_t length)
 {
 	static uint16_t size;
 
-	if (!flash_can_write(length)) {
+	if (!dfu_flash_ops->can_write(length)) {
 		dfu.state = dfuERROR;	
 		dfu.status = errADDRESS;
 		return 0;
@@ -125,7 +136,7 @@ static bool block_transmit(uint16_t length)
 		dfu.status = errUNKNOWN;
 		return 1;
 	}
-	got = flash_read(buf, length);
+	got = dfu_flash_ops->read(buf, length);
 	if (got < length) {
 		length = got;
 		dfu.state = dfuIDLE;
@@ -152,7 +163,7 @@ static bool my_setup(const struct setup_request *setup)
 		debug("DFU_DNLOAD\n");
 		if (dfu.state == dfuIDLE) {
 			next_block = setup->wValue;
-			flash_start();
+			dfu_flash_ops->start();
 		}
 		else if (dfu.state != dfuDNLOAD_IDLE) {
 			error("bad state\n");
@@ -171,7 +182,7 @@ static bool my_setup(const struct setup_request *setup)
 		}
 		if (!setup->wLength) {
 			debug("DONE\n");
-			flash_end_write();
+			dfu_flash_ops->end_write();
 			dfu.state = dfuIDLE;
 			did_download = 1;
 			return 1;
@@ -184,7 +195,7 @@ static bool my_setup(const struct setup_request *setup)
 		debug("DFU_UPLOAD\n");
 		if (dfu.state == dfuIDLE) {
 			next_block = setup->wValue;
-			flash_start();
+			dfu_flash_ops->start();
 		}
 		else if (dfu.state != dfuUPLOAD_IDLE)
 			return 0;
diff --git a/atusb/fw/usb/dfu.h b/atusb/fw/usb/dfu.h
index 206a3c0..b77758f 100644
--- a/atusb/fw/usb/dfu.h
+++ b/atusb/fw/usb/dfu.h
@@ -1,8 +1,8 @@
 /*
  * boot/dfu.h - DFU protocol constants and data structures
  *
- * Written 2008, 2011, 2013 by Werner Almesberger
- * Copyright 2008, 2011, 2013 Werner Almesberger
+ * Written 2008, 2011, 2013, 2014 by Werner Almesberger
+ * Copyright 2008, 2011, 2013, 2014 Werner Almesberger
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -86,11 +86,11 @@ struct dfu {
 };
 
 
-#define	DFU_ITF_DESCR(itf, proto)					     \
+#define	DFU_ITF_DESCR(itf, alt, proto)					     \
 	9,			/* bLength */				     \
 	USB_DT_INTERFACE,	/* bDescriptorType */			     \
 	(itf),			/* bInterfaceNumber */			     \
-	0,			/* bAlternateSetting */			     \
+	(alt),			/* bAlternateSetting */			     \
 	0,			/* bNumEndpoints */			     \
 	0xfe,			/* bInterfaceClass (application specific) */ \
 	0x01,			/* bInterfaceSubClass (device fw upgrade) */ \
@@ -98,15 +98,18 @@ struct dfu {
 	0,			/* iInterface */
 
 
+struct dfu_flash_ops {
+	void (*start)(void);
+	bool (*can_write)(uint16_t size);
+	void (*write)(const uint8_t *buf, uint16_t size);
+	void (*end_write)(void);
+	uint16_t (*read)(uint8_t *buf, uint16_t size);
+};
+
 extern struct dfu dfu;
+extern struct dfu_flash_ops *dfu_flash_ops;
 
 
-void flash_start(void);
-bool flash_can_write(uint16_t size);
-void flash_write(const uint8_t *buf, uint16_t size);
-void flash_end_write(void);
-uint16_t flash_read(uint8_t *buf, uint16_t size);
-
 bool dfu_setup_common(const struct setup_request *setup);
 bool dfu_my_descr(uint8_t type, uint8_t index, const uint8_t **reply,
     uint8_t *size);