diff --git a/libraries/AP_HAL/Scheduler.h b/libraries/AP_HAL/Scheduler.h
index 9f1456b94c..2490ab8205 100644
--- a/libraries/AP_HAL/Scheduler.h
+++ b/libraries/AP_HAL/Scheduler.h
@@ -8,7 +8,7 @@
 
 class AP_HAL::Scheduler {
 public:
-    Scheduler( AP_HAL::Periodic ) {}
+    Scheduler() {}
     virtual void     init() = 0;
     virtual void     delay(uint32_t ms) = 0;
     virtual uint32_t millis() = 0;
diff --git a/libraries/AP_HAL_AVR/Scheduler.cpp b/libraries/AP_HAL_AVR/Scheduler.cpp
index 6288246858..9fb55cd2fe 100644
--- a/libraries/AP_HAL_AVR/Scheduler.cpp
+++ b/libraries/AP_HAL_AVR/Scheduler.cpp
@@ -10,9 +10,9 @@ using namespace AP_HAL_AVR;
 #define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
 #define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
 
-static volatile unsigned long timer0_overflow_count = 0;
-static volatile unsigned long timer0_millis = 0;
-static unsigned char timer0_fract = 0;
+static volatile uint32_t timer0_overflow_count = 0;
+static volatile uint32_t timer0_millis = 0;
+static uint8_t timer0_fract = 0;
 
 void ArduinoScheduler::init() {
     // this needs to be called before setup() or some functions won't
@@ -92,8 +92,8 @@ SIGNAL(TIMER0_OVF_vect)
 {
 	// copy these to local variables so they can be stored in registers
 	// (volatile variables must be read from memory on every access)
-	unsigned long m = timer0_millis;
-	unsigned char f = timer0_fract;
+	uint32_t m = timer0_millis;
+	uint8_t f = timer0_fract;
 
 	m += MILLIS_INC;
 	f += FRACT_INC;
@@ -107,9 +107,9 @@ SIGNAL(TIMER0_OVF_vect)
 	timer0_overflow_count++;
 }
 
-unsigned long ArduinoScheduler::millis()
+uint32_t ArduinoScheduler::millis()
 {
-	unsigned long m;
+	uint32_t m;
 	uint8_t oldSREG = SREG;
 
 	// disable interrupts while we read timer0_millis or we might get an
@@ -121,8 +121,8 @@ unsigned long ArduinoScheduler::millis()
 	return m;
 }
 
-unsigned long ArduinoScheduler::micros() {
-	unsigned long m;
+uint32_t ArduinoScheduler::micros() {
+	uint32_t m;
 	uint8_t oldSREG = SREG, t;
 	
 	cli();
@@ -137,7 +137,7 @@ unsigned long ArduinoScheduler::micros() {
 	return ((m << 8) + t) * (64 / clockCyclesPerMicrosecond());
 }
 
-void ArduinoScheduler::delay(unsigned long ms)
+void ArduinoScheduler::delay(uint32_t ms)
 {
 	uint16_t start = (uint16_t)micros();
 
@@ -150,7 +150,7 @@ void ArduinoScheduler::delay(unsigned long ms)
 }
 
 /* Delay for the given number of microseconds.  Assumes a 8 or 16 MHz clock. */
-void ArduinoScheduler::delayMicroseconds(unsigned int us)
+void ArduinoScheduler::delay_microseconds(uint16_t us)
 {
 	// calling avrlib's delay_us() function with low values (e.g. 1 or
 	// 2 microseconds) gives delays longer than desired.
@@ -178,3 +178,6 @@ void ArduinoScheduler::delayMicroseconds(unsigned int us)
 	);
 }
 
+void ArduinoScheduler::register_delay_callback(void(*cb)(void)) {
+    /* XXX need to implement */
+}
diff --git a/libraries/AP_HAL_AVR/Scheduler.h b/libraries/AP_HAL_AVR/Scheduler.h
index 367462050f..cada9002b6 100644
--- a/libraries/AP_HAL_AVR/Scheduler.h
+++ b/libraries/AP_HAL_AVR/Scheduler.h
@@ -9,11 +9,12 @@ class AP_HAL_AVR::ArduinoScheduler : public AP_HAL::Scheduler {
 public:
     ArduinoScheduler() {}
     /* AP_HAL::Scheduler methods */
-    void          init();
-    void          delay(unsigned long ms);
-    unsigned long millis();
-    unsigned long micros();
-    void          delayMicroseconds(unsigned int us);
+    void     init();
+    void     delay(uint32_t ms);
+    uint32_t millis();
+    uint32_t micros();
+    void     delay_microseconds(uint16_t us);
+    void     register_delay_callback(void(*cb)(void));
 };
 
 #endif // __AP_HAL_AVR_SCHEDULER_H__