diff --git a/atusb/fw/board.h b/atusb/fw/board.h
index 09ec915..bb0b2cc 100644
--- a/atusb/fw/board.h
+++ b/atusb/fw/board.h
@@ -1,8 +1,8 @@
 /*
  * fw/board.h - Board-specific functions and definitions
  *
- * Written 2008-2011 by Werner Almesberger
- * Copyright 2008-2011 Werner Almesberger
+ * Written 2008-2011, 2013 by Werner Almesberger
+ * Copyright 2008-2011, 2013 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
@@ -13,6 +13,7 @@
 #ifndef BOARD_H
 #define	BOARD_H
 
+#include <stdbool.h>
 #include <stdint.h>
 
 
@@ -87,7 +88,7 @@ void panic(void);
 uint64_t timer_read(void);
 void timer_init(void);
 
-int gpio(uint8_t port, uint8_t data, uint8_t dir, uint8_t mask, uint8_t *res);
+bool gpio(uint8_t port, uint8_t data, uint8_t dir, uint8_t mask, uint8_t *res);
 void gpio_cleanup(void);
 
 void board_init(void);
diff --git a/atusb/fw/board_app.c b/atusb/fw/board_app.c
index d996593..a83b6c8 100644
--- a/atusb/fw/board_app.c
+++ b/atusb/fw/board_app.c
@@ -1,8 +1,8 @@
 /*
  * fw/board_app.c - Board-specific functions (for the application)
  *
- * Written 2011 by Werner Almesberger
- * Copyright 2011 Werner Almesberger
+ * Written 2011, 2013 by Werner Almesberger
+ * Copyright 2011, 2013 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
@@ -12,6 +12,7 @@
 
 
 #include <stddef.h>
+#include <stdbool.h>
 #include <stdint.h>
 
 #include <avr/io.h>
@@ -92,7 +93,7 @@ void timer_init(void)
 }
 
 
-int gpio(uint8_t port, uint8_t data, uint8_t dir, uint8_t mask, uint8_t *res)
+bool gpio(uint8_t port, uint8_t data, uint8_t dir, uint8_t mask, uint8_t *res)
 {
 	EIMSK = 0; /* recover INT_RF to ATUSB_GPIO_CLEANUP or an MCU reset */
 
diff --git a/atusb/fw/ep0.c b/atusb/fw/ep0.c
index 5bbe177..5c9fed4 100644
--- a/atusb/fw/ep0.c
+++ b/atusb/fw/ep0.c
@@ -1,8 +1,8 @@
 /*
  * fw/ep0.c - EP0 extension protocol
  *
- * Written 2008-2011 by Werner Almesberger
- * Copyright 2008-2011 Werner Almesberger
+ * Written 2008-2011, 2013 by Werner Almesberger
+ * Copyright 2008-2011, 2013 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
@@ -11,6 +11,7 @@
  */
 
 
+#include <stdbool.h>
 #include <stdint.h>
 #include <string.h>
 
@@ -57,7 +58,7 @@ static void do_buf_write(void *user)
 #define	BUILD_OFFSET	7	/* '#' plus "65535" plus ' ' */
 
 
-static int my_setup(const struct setup_request *setup)
+static bool my_setup(const struct setup_request *setup)
 {
 	uint16_t req = setup->bmRequestType | setup->bRequest << 8;
 	unsigned tmp;
@@ -254,7 +255,7 @@ static int my_setup(const struct setup_request *setup)
 }
 
 
-static int my_dfu_setup(const struct setup_request *setup)
+static bool my_dfu_setup(const struct setup_request *setup)
 {
 	switch (setup->bmRequestType | setup->bRequest << 8) {
 	case DFU_TO_DEV(DFU_DETACH):
diff --git a/atusb/fw/flash.c b/atusb/fw/flash.c
index 3aeea71..54d9a19 100644
--- a/atusb/fw/flash.c
+++ b/atusb/fw/flash.c
@@ -1,8 +1,8 @@
 /*
  * fw/flash.c - Board-specific flash functions
  *
- * Written 2011 by Werner Almesberger
- * Copyright 2011 Werner Almesberger
+ * Written 2011, 2013 by Werner Almesberger
+ * Copyright 2011, 2013 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
@@ -11,6 +11,7 @@
  */
 
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #include <avr/boot.h>
@@ -29,7 +30,7 @@ void flash_start(void)
 }
 
 
-int flash_can_write(uint16_t size)
+bool flash_can_write(uint16_t size)
 {
 	return payload+size <= BOOT_ADDR;
 }
diff --git a/atusb/fw/mac.c b/atusb/fw/mac.c
index ded7f96..9030dce 100644
--- a/atusb/fw/mac.c
+++ b/atusb/fw/mac.c
@@ -118,7 +118,7 @@ static void change_state(uint8_t new)
 }
 
 
-int mac_rx(int on)
+bool mac_rx(int on)
 {
 	if (on) {
 		mac_irq = handle_irq;
@@ -178,7 +178,7 @@ static void do_tx(void *user)
 }
 
 
-int mac_tx(uint16_t flags, uint16_t len)
+bool mac_tx(uint16_t flags, uint16_t len)
 {
 	if (len > MAX_PSDU)
 		return 0;
diff --git a/atusb/fw/mac.h b/atusb/fw/mac.h
index b6eed97..6b06730 100644
--- a/atusb/fw/mac.h
+++ b/atusb/fw/mac.h
@@ -13,13 +13,14 @@
 #ifndef MAC_H
 #define	MAC_H
 
+#include <stdbool.h>
 #include <stdint.h>
 
 
 extern int (*mac_irq)(void);
 
-int mac_rx(int on);
-int mac_tx(uint16_t flags, uint16_t len);
+bool mac_rx(int on);
+bool mac_tx(uint16_t flags, uint16_t len);
 void mac_reset(void);
 
 #endif /* !MAC_H */
diff --git a/atusb/fw/sernum.c b/atusb/fw/sernum.c
index e473d78..41e434c 100644
--- a/atusb/fw/sernum.c
+++ b/atusb/fw/sernum.c
@@ -1,8 +1,8 @@
 /*
  * fw/sernum.c - ATUSB serial number
  *
- * Written 2008-2011 by Werner Almesberger
- * Copyright 2008-2011 Werner Almesberger
+ * Written 2008-2011, 2013 by Werner Almesberger
+ * Copyright 2008-2011, 2013 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
@@ -11,6 +11,7 @@
  */
 
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #include "usb.h"
@@ -26,7 +27,7 @@ static const uint8_t string_descriptor_0[] = {
 };
 
 
-int sernum_get_descr(uint8_t type, uint8_t index, const uint8_t **reply,
+bool sernum_get_descr(uint8_t type, uint8_t index, const uint8_t **reply,
     uint8_t *size)
 {
 	if (type != USB_DT_STRING)
diff --git a/atusb/fw/sernum.h b/atusb/fw/sernum.h
index 1005618..31a8e27 100644
--- a/atusb/fw/sernum.h
+++ b/atusb/fw/sernum.h
@@ -1,8 +1,8 @@
 /*
  * fw/sernum.h - ATUSB serial number
  *
- * Written 2011 by Werner Almesberger
- * Copyright 2011 Werner Almesberger
+ * Written 2011, 2013 by Werner Almesberger
+ * Copyright 2011, 2013 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
@@ -13,6 +13,7 @@
 #ifndef SERNUM_H
 #define	SERNUM_H
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #include "board.h"
@@ -20,12 +21,12 @@
 
 #ifdef HAS_BOARD_SERNUM
 
-int sernum_get_descr(uint8_t type, uint8_t index, const uint8_t **reply,
+bool sernum_get_descr(uint8_t type, uint8_t index, const uint8_t **reply,
     uint8_t *size);
 
 #else /* HAS_BOARD_SERNUM */
 
-static inline int sernum_get_descr(uint8_t type, uint8_t index,
+static inline bool sernum_get_descr(uint8_t type, uint8_t index,
     const uint8_t **reply, uint8_t *size)
 {
 	return 0;
diff --git a/atusb/fw/spi.c b/atusb/fw/spi.c
index 047523f..91a2de9 100644
--- a/atusb/fw/spi.c
+++ b/atusb/fw/spi.c
@@ -1,8 +1,8 @@
 /*
  * fw/spi.c - ATmega8 family SPI I/O
  *
- * Written 2011 by Werner Almesberger
- * Copyright 2011 Werner Almesberger
+ * Written 2011, 2013 by Werner Almesberger
+ * Copyright 2011, 2013 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
@@ -11,6 +11,7 @@
  */
 
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #include <avr/io.h>
@@ -19,7 +20,7 @@
 #include "spi.h"
 
 
-static int spi_initialized = 0;
+static bool spi_initialized = 0;
 
 
 void spi_begin(void)
diff --git a/atusb/fw/usb/atu2.c b/atusb/fw/usb/atu2.c
index 5d078ae..17868a5 100644
--- a/atusb/fw/usb/atu2.c
+++ b/atusb/fw/usb/atu2.c
@@ -1,8 +1,8 @@
 /*
  * fw/usb/atu2.c - Chip-specific driver for Atmel ATxxxU2 USB chips
  *
- * Written 2008-2011 by Werner Almesberger
- * Copyright 2008-2011 Werner Almesberger
+ * Written 2008-2011, 2013 by Werner Almesberger
+ * Copyright 2008-2011, 2013 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
@@ -18,6 +18,7 @@
  * - enumeration often encounters an error -71 (from which it recovers)
  */
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #define F_CPU   8000000UL
@@ -59,11 +60,10 @@ static void enable_addr(void *user)
 }
 
 
-int set_addr(uint8_t addr)
+void set_addr(uint8_t addr)
 {
 	UDADDR = addr;
 	usb_send(&eps[0], NULL, 0, enable_addr, NULL);
-	return 1;
 }
 
 
@@ -76,7 +76,7 @@ void usb_ep_change(struct ep_descr *ep)
 }
 
 
-static int ep_setup(void)
+static bool ep_setup(void)
 {
 	struct setup_request setup;
 
@@ -96,7 +96,7 @@ static int ep_setup(void)
 }
 
 
-static int ep_rx(struct ep_descr *ep)
+static bool ep_rx(struct ep_descr *ep)
 {
 	uint8_t size;
 
diff --git a/atusb/fw/usb/dfu.c b/atusb/fw/usb/dfu.c
index 83c52d5..996bac8 100644
--- a/atusb/fw/usb/dfu.c
+++ b/atusb/fw/usb/dfu.c
@@ -1,8 +1,8 @@
 /*
  * boot/dfu.c - DFU protocol engine
  *
- * Written 2008-2011 by Werner Almesberger
- * Copyright 2008-2011 Werner Almesberger
+ * Written 2008-2011, 2013 by Werner Almesberger
+ * Copyright 2008-2011, 2013 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
@@ -25,6 +25,7 @@
  */
 
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #include "usb.h"
@@ -81,7 +82,7 @@ const uint8_t config_descriptor[] = {
 
 
 static uint16_t next_block = 0;
-static int did_download;
+static bool did_download;
 
 
 static uint8_t buf[EP0_SIZE];
@@ -95,7 +96,7 @@ static void block_write(void *user)
 }
 
 
-static int block_receive(uint16_t length)
+static bool block_receive(uint16_t length)
 {
 	static uint16_t size;
 
@@ -115,7 +116,7 @@ static int block_receive(uint16_t length)
 }
 
 
-static int block_transmit(uint16_t length)
+static bool block_transmit(uint16_t length)
 {
 	uint16_t got;
 
@@ -134,9 +135,9 @@ static int block_transmit(uint16_t length)
 }
 
 
-static int my_setup(const struct setup_request *setup)
+static bool my_setup(const struct setup_request *setup)
 {
-	int ok;
+	bool ok;
 
 	switch (setup->bmRequestType | setup->bRequest << 8) {
 	case DFU_TO_DEV(DFU_DETACH):
diff --git a/atusb/fw/usb/dfu.h b/atusb/fw/usb/dfu.h
index 691be2b..206a3c0 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 by Werner Almesberger
- * Copyright 2008, 2011 Werner Almesberger
+ * Written 2008, 2011, 2013 by Werner Almesberger
+ * Copyright 2008, 2011, 2013 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
@@ -14,6 +14,7 @@
 #ifndef DFU_H
 #define DFU_H
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #include "usb.h"
@@ -101,13 +102,13 @@ extern struct dfu dfu;
 
 
 void flash_start(void);
-int flash_can_write(uint16_t size);
+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);
 
-int dfu_setup_common(const struct setup_request *setup);
-int dfu_my_descr(uint8_t type, uint8_t index, const uint8_t **reply,
+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);
 
 void dfu_init(void);
diff --git a/atusb/fw/usb/dfu_common.c b/atusb/fw/usb/dfu_common.c
index 6d025b0..a339c38 100644
--- a/atusb/fw/usb/dfu_common.c
+++ b/atusb/fw/usb/dfu_common.c
@@ -1,8 +1,8 @@
 /*
  * boot/dfu_common.c - DFU protocol engine parts common to App/DFU
  *
- * Written 2008-2011 by Werner Almesberger
- * Copyright 2008-2011 Werner Almesberger
+ * Written 2008-2011, 2013 by Werner Almesberger
+ * Copyright 2008-2011, 2013 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
@@ -25,6 +25,7 @@
  */
 
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #include "usb.h"
@@ -65,7 +66,7 @@ struct dfu dfu = {
 };
 
 
-int dfu_setup_common(const struct setup_request *setup)
+bool dfu_setup_common(const struct setup_request *setup)
 {
 	switch (setup->bmRequestType | setup->bRequest << 8) {
 	case DFU_FROM_DEV(DFU_GETSTATUS):
@@ -89,7 +90,7 @@ int dfu_setup_common(const struct setup_request *setup)
 }
 
 
-int dfu_my_descr(uint8_t type, uint8_t index, const uint8_t **reply,
+bool dfu_my_descr(uint8_t type, uint8_t index, const uint8_t **reply,
     uint8_t *size)
 {
 	if (type != DFU_DT_FUNCTIONAL)
diff --git a/atusb/fw/usb/usb.c b/atusb/fw/usb/usb.c
index 3ab2688..4fde778 100644
--- a/atusb/fw/usb/usb.c
+++ b/atusb/fw/usb/usb.c
@@ -1,8 +1,8 @@
 /*
  * fw/usb/usb.c - USB hardware setup and standard device requests
  *
- * Written 2008-2011 by Werner Almesberger
- * Copyright 2008-2011 Werner Almesberger
+ * Written 2008-2011, 2013 by Werner Almesberger
+ * Copyright 2008-2011, 2013 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
@@ -16,6 +16,7 @@
  * - should support EP clearing and stalling
  */
 
+#include <stdbool.h>
 #include <stdint.h>
 
 #include "usb.h"
@@ -33,9 +34,9 @@ extern void panic(void);
 #define BUG_ON(cond)
 #endif
 
-int (*user_setup)(const struct setup_request *setup);
+bool (*user_setup)(const struct setup_request *setup);
 void (*user_set_interface)(int nth);
-int (*user_get_descriptor)(uint8_t type, uint8_t index,
+bool (*user_get_descriptor)(uint8_t type, uint8_t index,
     const uint8_t **reply, uint8_t *size);
 void (*user_reset)(void);
 
@@ -53,7 +54,7 @@ void usb_io(struct ep_descr *ep, enum ep_state state, uint8_t *buf,
 }
 
 
-static int get_descriptor(uint8_t type, uint8_t index, uint16_t length)
+static bool get_descriptor(uint8_t type, uint8_t index, uint16_t length)
 {
 	const uint8_t *reply;
 	uint8_t size;
@@ -82,7 +83,7 @@ static int get_descriptor(uint8_t type, uint8_t index, uint16_t length)
 }
 
 
-int handle_setup(const struct setup_request *setup)
+bool handle_setup(const struct setup_request *setup)
 {
 	switch (setup->bmRequestType | setup->bRequest << 8) {
 
diff --git a/atusb/fw/usb/usb.h b/atusb/fw/usb/usb.h
index f508091..90dd423 100644
--- a/atusb/fw/usb/usb.h
+++ b/atusb/fw/usb/usb.h
@@ -1,8 +1,8 @@
 /*
  * fw/usb//usb.h - USB hardware setup and standard device requests
  *
- * Written 2008, 2009, 2011 by Werner Almesberger
- * Copyright 2008, 2009, 2011 Werner Almesberger
+ * Written 2008, 2009, 2011, 2013 by Werner Almesberger
+ * Copyright 2008, 2009, 2011, 2013 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
@@ -15,6 +15,7 @@
 #define USB_H
 
 
+#include <stdbool.h>
 #include <stdint.h>
 
 
@@ -132,9 +133,9 @@ extern const uint8_t device_descriptor[];
 extern const uint8_t config_descriptor[];
 extern struct ep_descr eps[];
 
-extern int (*user_setup)(const struct setup_request *setup);
+extern bool (*user_setup)(const struct setup_request *setup);
 extern void (*user_set_interface)(int nth);
-extern int (*user_get_descriptor)(uint8_t type, uint8_t index,
+extern bool (*user_get_descriptor)(uint8_t type, uint8_t index,
     const uint8_t **reply, uint8_t *size);
 extern void (*user_reset)(void);
 
@@ -148,8 +149,8 @@ extern void (*user_reset)(void);
 void usb_io(struct ep_descr *ep, enum ep_state state, uint8_t *buf,
     uint8_t size, void (*callback)(void *user), void *user);
 
-int handle_setup(const struct setup_request *setup);
-int set_addr(uint8_t addr);
+bool handle_setup(const struct setup_request *setup);
+void set_addr(uint8_t addr);
 void usb_ep_change(struct ep_descr *ep);
 void usb_reset(void);
 void usb_init(void);