diff --git a/libraries/AP_HAL_AVR_SITL/HAL_AVR_SITL_Class.cpp b/libraries/AP_HAL_AVR_SITL/HAL_AVR_SITL_Class.cpp
index af52587e56..54fa029563 100644
--- a/libraries/AP_HAL_AVR_SITL/HAL_AVR_SITL_Class.cpp
+++ b/libraries/AP_HAL_AVR_SITL/HAL_AVR_SITL_Class.cpp
@@ -31,7 +31,10 @@ static SITLRCInput  sitlRCInput(&sitlState);
 static SITLRCOutput sitlRCOutput(&sitlState);
 static SITLAnalogIn sitlAnalogIn(&sitlState);
 
+// use the Empty HAL for hardware we don't emulate
 static Empty::EmptyGPIO emptyGPIO;
+static Empty::EmptyI2CDriver emptyI2C;
+static Empty::EmptySPIDeviceManager emptySPI;
 
 static SITLUARTDriver sitlUart0Driver(0, &sitlState);
 static SITLUARTDriver sitlUart1Driver(1, &sitlState);
@@ -42,8 +45,8 @@ HAL_AVR_SITL::HAL_AVR_SITL() :
 	    &sitlUart0Driver,  /* uartA */
         &sitlUart1Driver, /* uartB */
         &sitlUart2Driver,  /* uartC */
-        NULL, /* i2c */
-        NULL, /* spi */
+        &emptyI2C, /* i2c */
+        &emptySPI, /* spi */
         &sitlAnalogIn, /* analogin */
         &sitlEEPROMStorage, /* storage */
         &consoleDriver, /* console */
diff --git a/libraries/AP_HAL_AVR_SITL/RCInput.cpp b/libraries/AP_HAL_AVR_SITL/RCInput.cpp
index 6fad9b71bc..041b4f328f 100644
--- a/libraries/AP_HAL_AVR_SITL/RCInput.cpp
+++ b/libraries/AP_HAL_AVR_SITL/RCInput.cpp
@@ -13,10 +13,11 @@ void SITLRCInput::init(void* machtnichts)
 }
 
 uint8_t SITLRCInput::valid() {
-    return 0;
+    return _sitlState->pwm_valid;
 }
 
 uint16_t SITLRCInput::read(uint8_t ch) {
+    _sitlState->pwm_valid = false;
     return _override[ch]? _override[ch] : _sitlState->pwm_input[ch];
 }
 
@@ -24,7 +25,9 @@ uint8_t SITLRCInput::read(uint16_t* periods, uint8_t len) {
     for (uint8_t i=0; i<len; i++) {
 	periods[i] = _override[i]? _override[i] : _sitlState->pwm_input[i];
     }
-    return len;
+    uint8_t v = _sitlState->pwm_valid;
+    _sitlState->pwm_valid = false;
+    return v;
 }
 
 bool SITLRCInput::set_overrides(int16_t *overrides, uint8_t len) {
diff --git a/libraries/AP_HAL_AVR_SITL/RCInput.h b/libraries/AP_HAL_AVR_SITL/RCInput.h
index 16ee291338..34a4b69330 100644
--- a/libraries/AP_HAL_AVR_SITL/RCInput.h
+++ b/libraries/AP_HAL_AVR_SITL/RCInput.h
@@ -19,8 +19,10 @@ public:
     bool set_overrides(int16_t *overrides, uint8_t len);
     bool set_override(uint8_t channel, int16_t override);
     void clear_overrides();
+
 private:
     SITL_State *_sitlState;
+    bool _valid;
 
     /* override state */
     uint16_t _override[8];
diff --git a/libraries/AP_HAL_AVR_SITL/SITL_State.cpp b/libraries/AP_HAL_AVR_SITL/SITL_State.cpp
index 6dfb8405ec..91404f2093 100644
--- a/libraries/AP_HAL_AVR_SITL/SITL_State.cpp
+++ b/libraries/AP_HAL_AVR_SITL/SITL_State.cpp
@@ -42,6 +42,7 @@ int SITL_State::_sitl_fd;
 SITL *SITL_State::_sitl;
 uint16_t SITL_State::pwm_output[11];
 uint16_t SITL_State::pwm_input[8];
+bool SITL_State::pwm_valid;
 
 // catch floating point exceptions
 void SITL_State::_sig_fpe(int signum)
@@ -185,6 +186,8 @@ void SITL_State::_setup_fdm(void)
 void SITL_State::_timer_handler(int signum)
 {
 	static uint32_t last_update_count;
+    static uint32_t last_pwm_input;
+
 	static bool in_timer;
 
 	if (in_timer || ((SITLScheduler *)hal.scheduler)->interrupts_are_blocked()) {
@@ -204,7 +207,7 @@ void SITL_State::_timer_handler(int signum)
 	static uint16_t count = 0;
 	static uint32_t last_report;
         
-    	count++;
+    count++;
 	if (millis() - last_report > 1000) {
 		fprintf(stdout, "TH %u cps\n", count);
 		count = 0;
@@ -212,6 +215,12 @@ void SITL_State::_timer_handler(int signum)
 	}
 #endif
 
+    // simulate RC input at 50Hz
+    if (hal.scheduler->millis() - last_pwm_input >= 20) {
+        last_pwm_input = hal.scheduler->millis();
+        pwm_valid = true;
+    }
+
 	/* check for packet from flight sim */
 	_fdm_input();
 
@@ -287,7 +296,9 @@ void SITL_State::_fdm_input(void)
 			return;
 		}
 
-		_sitl->state = d.fg_pkt;
+        if (_sitl != NULL) {
+            _sitl->state = d.fg_pkt;
+        }
 		_update_count++;
 
 		count++;
diff --git a/libraries/AP_HAL_AVR_SITL/SITL_State.h b/libraries/AP_HAL_AVR_SITL/SITL_State.h
index 5338d877d0..655decf3c6 100644
--- a/libraries/AP_HAL_AVR_SITL/SITL_State.h
+++ b/libraries/AP_HAL_AVR_SITL/SITL_State.h
@@ -37,6 +37,7 @@ public:
     ssize_t gps_read(int fd, void *buf, size_t count);
     static uint16_t pwm_output[11];
     static uint16_t pwm_input[8];
+    static bool pwm_valid;
     static void loop_hook(void);
 
     // simulated airspeed