diff --git a/libraries/AP_ADC/AP_ADC_ADS1115.cpp b/libraries/AP_ADC/AP_ADC_ADS1115.cpp
index 4bc5d8af5f..b098c889a5 100644
--- a/libraries/AP_ADC/AP_ADC_ADS1115.cpp
+++ b/libraries/AP_ADC/AP_ADC_ADS1115.cpp
@@ -130,7 +130,7 @@ bool AP_ADC_ADS1115::init()
 
     _gain = ADS1115_PGA_4P096;
 
-    _dev->register_periodic_callback(100000, FUNCTOR_BIND_MEMBER(&AP_ADC_ADS1115::_update, bool));
+    _dev->register_periodic_callback(100000, FUNCTOR_BIND_MEMBER(&AP_ADC_ADS1115::_update, void));
 
     return true;
 }
@@ -200,23 +200,23 @@ float AP_ADC_ADS1115::_convert_register_data_to_mv(int16_t word) const
     return (float) word * pga;
 }
 
-bool AP_ADC_ADS1115::_update()
+void AP_ADC_ADS1115::_update()
 {
     uint8_t config[2];
     be16_t val;
 
     if (!_dev->read_registers(ADS1115_RA_CONFIG, config, sizeof(config))) {
         error("_dev->read_registers failed in ADS1115");
-        return true;
+        return;
     }
 
     /* check rdy bit */
     if ((config[1] & 0x80) != 0x80 ) {
-        return true;
+        return;
     }
 
     if (!_dev->read_registers(ADS1115_RA_CONVERSION, (uint8_t *)&val,  sizeof(val))) {
-        return true;
+        return;
     }
 
     float sample = _convert_register_data_to_mv(be16toh(val));
@@ -227,6 +227,4 @@ bool AP_ADC_ADS1115::_update()
     /* select next channel */
     _channel_to_read = (_channel_to_read + 1) % _channels_number;
     _start_conversion(_channel_to_read);
-
-    return true;
 }
diff --git a/libraries/AP_ADC/AP_ADC_ADS1115.h b/libraries/AP_ADC/AP_ADC_ADS1115.h
index 2f49a9dc8a..98e6544875 100644
--- a/libraries/AP_ADC/AP_ADC_ADS1115.h
+++ b/libraries/AP_ADC/AP_ADC_ADS1115.h
@@ -36,7 +36,7 @@ private:
     int                 _channel_to_read;
     adc_report_s        *_samples;
 
-    bool _update();
+    void _update();
     bool _start_conversion(uint8_t channel);
 
     float _convert_register_data_to_mv(int16_t word) const;
diff --git a/libraries/AP_Airspeed/AP_Airspeed_MS4525.cpp b/libraries/AP_Airspeed/AP_Airspeed_MS4525.cpp
index 4905945814..9f227fc35f 100644
--- a/libraries/AP_Airspeed/AP_Airspeed_MS4525.cpp
+++ b/libraries/AP_Airspeed/AP_Airspeed_MS4525.cpp
@@ -84,7 +84,7 @@ bool AP_Airspeed_MS4525::init()
     _dev->set_retries(2);
     
     _dev->register_periodic_callback(20000,
-                                     FUNCTOR_BIND_MEMBER(&AP_Airspeed_MS4525::_timer, bool));
+                                     FUNCTOR_BIND_MEMBER(&AP_Airspeed_MS4525::_timer, void));
     return true;
 }
 
@@ -173,18 +173,17 @@ void AP_Airspeed_MS4525::_voltage_correction(float &diff_press_pa, float &temper
 }
 
 // 50Hz timer
-bool AP_Airspeed_MS4525::_timer()
+void AP_Airspeed_MS4525::_timer()
 {
     if (_measurement_started_ms == 0) {
         _measure();
-        return true;
+        return;
     }
     if ((AP_HAL::millis() - _measurement_started_ms) > 10) {
         _collect();
         // start a new measurement
         _measure();
     }
-    return true;
 }
 
 // return the current differential_pressure in Pascal
diff --git a/libraries/AP_Airspeed/AP_Airspeed_MS4525.h b/libraries/AP_Airspeed/AP_Airspeed_MS4525.h
index b89edcc69e..cb3208cf21 100644
--- a/libraries/AP_Airspeed/AP_Airspeed_MS4525.h
+++ b/libraries/AP_Airspeed/AP_Airspeed_MS4525.h
@@ -45,7 +45,7 @@ public:
 private:
     void _measure();
     void _collect();
-    bool _timer();
+    void _timer();
     void _voltage_correction(float &diff_press_pa, float &temperature);
 
     float _temp_sum;
diff --git a/libraries/AP_Airspeed/AP_Airspeed_MS5525.cpp b/libraries/AP_Airspeed/AP_Airspeed_MS5525.cpp
index 1c8f8e71b2..75f0315c39 100644
--- a/libraries/AP_Airspeed/AP_Airspeed_MS5525.cpp
+++ b/libraries/AP_Airspeed/AP_Airspeed_MS5525.cpp
@@ -96,7 +96,7 @@ bool AP_Airspeed_MS5525::init()
 
     // read at 80Hz
     dev->register_periodic_callback(1000000UL/80U,
-                                    FUNCTOR_BIND_MEMBER(&AP_Airspeed_MS5525::timer, bool));
+                                    FUNCTOR_BIND_MEMBER(&AP_Airspeed_MS5525::timer, void));
     return true;
 }
 
@@ -219,7 +219,7 @@ void AP_Airspeed_MS5525::calculate(void)
 }
 
 // 50Hz timer
-bool AP_Airspeed_MS5525::timer()
+void AP_Airspeed_MS5525::timer()
 {
     uint32_t adc_val = read_adc();
 
@@ -241,12 +241,10 @@ bool AP_Airspeed_MS5525::timer()
 
     uint8_t next_cmd = next_state == 0 ? REG_CONVERT_TEMPERATURE : REG_CONVERT_PRESSURE;
     if (!dev->transfer(&next_cmd, 1, nullptr, 0)) {
-        return true;
+        return;
     }
 
     state = next_state;
-    
-    return true;
 }
 
 // return the current differential_pressure in Pascal
diff --git a/libraries/AP_Airspeed/AP_Airspeed_MS5525.h b/libraries/AP_Airspeed/AP_Airspeed_MS5525.h
index c4cdd5c213..e5e227a4f7 100644
--- a/libraries/AP_Airspeed/AP_Airspeed_MS5525.h
+++ b/libraries/AP_Airspeed/AP_Airspeed_MS5525.h
@@ -45,7 +45,7 @@ public:
 private:
     void measure();
     void collect();
-    bool timer();
+    void timer();
     bool read_prom(void);
     uint16_t crc4_prom(void);
     int32_t read_adc();
diff --git a/libraries/AP_Baro/AP_Baro_BMP085.cpp b/libraries/AP_Baro/AP_Baro_BMP085.cpp
index 4873e0ebec..95ec3c92dc 100644
--- a/libraries/AP_Baro/AP_Baro_BMP085.cpp
+++ b/libraries/AP_Baro/AP_Baro_BMP085.cpp
@@ -81,16 +81,16 @@ AP_Baro_BMP085::AP_Baro_BMP085(AP_Baro &baro, AP_HAL::OwnPtr<AP_HAL::I2CDevice>
 
     sem->give();
 
-    _dev->register_periodic_callback(20000, FUNCTOR_BIND_MEMBER(&AP_Baro_BMP085::_timer, bool));
+    _dev->register_periodic_callback(20000, FUNCTOR_BIND_MEMBER(&AP_Baro_BMP085::_timer, void));
 }
 
 /*
   This is a state machine. Acumulate a new sensor reading.
  */
-bool AP_Baro_BMP085::_timer(void)
+void AP_Baro_BMP085::_timer(void)
 {
     if (!_data_ready()) {
-        return true;
+        return;
     }
 
     if (_state == 0) {
@@ -106,7 +106,6 @@ bool AP_Baro_BMP085::_timer(void)
     } else {
         _cmd_read_pressure();
     }
-    return true;
 }
 
 /*
diff --git a/libraries/AP_Baro/AP_Baro_BMP085.h b/libraries/AP_Baro/AP_Baro_BMP085.h
index cdc3de3cdf..7bf345cdec 100644
--- a/libraries/AP_Baro/AP_Baro_BMP085.h
+++ b/libraries/AP_Baro/AP_Baro_BMP085.h
@@ -23,8 +23,8 @@ private:
     void _calculate();
     bool _data_ready();
 
-    bool _timer(void);
-    
+    void _timer(void);
+
     AP_HAL::OwnPtr<AP_HAL::I2CDevice> _dev;
     AP_HAL::DigitalSource *_eoc;
 
diff --git a/libraries/AP_Baro/AP_Baro_MS5611.cpp b/libraries/AP_Baro/AP_Baro_MS5611.cpp
index 90cbb262ef..5088bc5e06 100644
--- a/libraries/AP_Baro/AP_Baro_MS5611.cpp
+++ b/libraries/AP_Baro/AP_Baro_MS5611.cpp
@@ -137,7 +137,7 @@ bool AP_Baro_MS56XX::_init()
 
     /* Request 100Hz update */
     _dev->register_periodic_callback(10 * USEC_PER_MSEC,
-                                     FUNCTOR_BIND_MEMBER(&AP_Baro_MS56XX::_timer, bool));
+                                     FUNCTOR_BIND_MEMBER(&AP_Baro_MS56XX::_timer, void));
     return true;
 }
 
@@ -259,7 +259,7 @@ bool AP_Baro_MS56XX::_read_prom_5637(uint16_t prom[8])
  * as fast as pressure. Hence we reuse the same temperature for 4 samples of
  * pressure.
 */
-bool AP_Baro_MS56XX::_timer(void)
+void AP_Baro_MS56XX::_timer(void)
 {
     uint8_t next_cmd;
     uint8_t next_state;
@@ -278,7 +278,7 @@ bool AP_Baro_MS56XX::_timer(void)
     next_cmd = next_state == 0 ? ADDR_CMD_CONVERT_TEMPERATURE
                                : ADDR_CMD_CONVERT_PRESSURE;
     if (!_dev->transfer(&next_cmd, 1, nullptr, 0)) {
-        return true;
+        return;
     }
 
     /* if we had a failed read we are all done */
@@ -286,13 +286,13 @@ bool AP_Baro_MS56XX::_timer(void)
         // a failed read can mean the next returned value will be
         // corrupt, we must discard it
         _discard_next = true;
-        return true;
+        return;
     }
 
     if (_discard_next) {
         _discard_next = false;
         _state = next_state;
-        return true;
+        return;
     }
 
     if (_sem->take(HAL_SEMAPHORE_BLOCK_FOREVER)) {
@@ -306,8 +306,6 @@ bool AP_Baro_MS56XX::_timer(void)
         _sem->give();
         _state = next_state;
     }
-
-    return true;
 }
 
 void AP_Baro_MS56XX::_update_and_wrap_accumulator(uint32_t *accum, uint32_t val,
diff --git a/libraries/AP_Baro/AP_Baro_MS5611.h b/libraries/AP_Baro/AP_Baro_MS5611.h
index e230f4591a..d74b136003 100644
--- a/libraries/AP_Baro/AP_Baro_MS5611.h
+++ b/libraries/AP_Baro/AP_Baro_MS5611.h
@@ -46,7 +46,7 @@ private:
     uint16_t _read_prom_word(uint8_t word);
     uint32_t _read_adc();
 
-    bool _timer();
+    void _timer();
 
     AP_HAL::OwnPtr<AP_HAL::Device> _dev;
 
diff --git a/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_I2C.cpp b/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_I2C.cpp
index 0b0ae6da88..25e57f0c2f 100644
--- a/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_I2C.cpp
+++ b/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_I2C.cpp
@@ -30,7 +30,7 @@ AP_BattMonitor_SMBus_I2C::AP_BattMonitor_SMBus_I2C(AP_BattMonitor &mon, uint8_t
     : AP_BattMonitor_SMBus(mon, instance, mon_state)
     , _dev(std::move(dev))
 {
-    _dev->register_periodic_callback(100000, FUNCTOR_BIND_MEMBER(&AP_BattMonitor_SMBus_I2C::timer, bool));
+    _dev->register_periodic_callback(100000, FUNCTOR_BIND_MEMBER(&AP_BattMonitor_SMBus_I2C::timer, void));
 }
 
 /// Read the battery voltage and current.  Should be called at 10hz
@@ -39,7 +39,7 @@ void AP_BattMonitor_SMBus_I2C::read()
     // nothing to do - all done in timer()
 }
 
-bool AP_BattMonitor_SMBus_I2C::timer()
+void AP_BattMonitor_SMBus_I2C::timer()
 {
     uint16_t data;
     uint8_t buff[4];
@@ -62,7 +62,6 @@ bool AP_BattMonitor_SMBus_I2C::timer()
     if ((tnow - _state.last_time_micros) > AP_BATTMONITOR_SMBUS_TIMEOUT_MICROS) {
         _state.healthy = false;
     }
-    return true;
 }
 
 // read word from register
diff --git a/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_I2C.h b/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_I2C.h
index a84e8aabf8..dc92e3259f 100644
--- a/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_I2C.h
+++ b/libraries/AP_BattMonitor/AP_BattMonitor_SMBus_I2C.h
@@ -23,7 +23,7 @@ public:
 
 private:
 
-    bool timer(void);
+    void timer(void);
 
     // read word from register
     // returns true if read was successful, false if failed
diff --git a/libraries/AP_Compass/AP_Compass_AK09916.cpp b/libraries/AP_Compass/AP_Compass_AK09916.cpp
index d11ea802db..439a04d068 100644
--- a/libraries/AP_Compass/AP_Compass_AK09916.cpp
+++ b/libraries/AP_Compass/AP_Compass_AK09916.cpp
@@ -103,7 +103,7 @@ bool AP_Compass_AK09916::init()
 
     // call timer() at 100Hz
     dev->register_periodic_callback(10000,
-                                    FUNCTOR_BIND_MEMBER(&AP_Compass_AK09916::timer, bool));
+                                    FUNCTOR_BIND_MEMBER(&AP_Compass_AK09916::timer, void));
 
     return true;
 
@@ -112,7 +112,7 @@ fail:
     return false;
 }
 
-bool AP_Compass_AK09916::timer()
+void AP_Compass_AK09916::timer()
 {
     struct PACKED {
         int16_t magx;
@@ -131,7 +131,7 @@ bool AP_Compass_AK09916::timer()
     if (!dev->read_registers(REG_ST1, &st1, 1) || !(st1 & 1)) {
         goto check_registers;
     }
-    
+
     if (!dev->read_registers(REG_HXL, (uint8_t *)&data, sizeof(data))) {
         goto check_registers;
     }
@@ -155,7 +155,6 @@ bool AP_Compass_AK09916::timer()
 
 check_registers:
     dev->check_next_register();
-    return true;
 }
 
 void AP_Compass_AK09916::read()
diff --git a/libraries/AP_Compass/AP_Compass_AK09916.h b/libraries/AP_Compass/AP_Compass_AK09916.h
index a9a7e4d235..45541ed00b 100644
--- a/libraries/AP_Compass/AP_Compass_AK09916.h
+++ b/libraries/AP_Compass/AP_Compass_AK09916.h
@@ -49,7 +49,7 @@ private:
      * Device periodic callback to read data from the sensor.
      */
     bool init();
-    bool timer();
+    void timer();
 
     uint8_t compass_instance;
     Vector3f accum;
diff --git a/libraries/AP_Compass/AP_Compass_AK8963.cpp b/libraries/AP_Compass/AP_Compass_AK8963.cpp
index 87089122f4..e865bfac9f 100644
--- a/libraries/AP_Compass/AP_Compass_AK8963.cpp
+++ b/libraries/AP_Compass/AP_Compass_AK8963.cpp
@@ -168,7 +168,7 @@ bool AP_Compass_AK8963::init()
     bus_sem->give();
 
     /* timer needs to be called every 10ms so set the freq_div to 10 */
-    if (!_bus->register_periodic_callback(10000, FUNCTOR_BIND_MEMBER(&AP_Compass_AK8963::_update, bool))) {
+    if (!_bus->register_periodic_callback(10000, FUNCTOR_BIND_MEMBER(&AP_Compass_AK8963::_update, void))) {
         // fallback to timer
         _timesliced = hal.scheduler->register_timer_process(FUNCTOR_BIND_MEMBER(&AP_Compass_AK8963::_update_timer, void), 10);
     }
@@ -215,26 +215,26 @@ void AP_Compass_AK8963::_make_factory_sensitivity_adjustment(Vector3f& field) co
     field.z *= _magnetometer_ASA[2];
 }
 
-bool AP_Compass_AK8963::_update()
+void AP_Compass_AK8963::_update()
 {
     struct sample_regs regs;
     Vector3f raw_field;
     uint32_t time_us = AP_HAL::micros();
 
     if (!_bus->block_read(AK8963_HXL, (uint8_t *) &regs, sizeof(regs))) {
-        goto fail;
+        return;
     }
 
     /* Check for overflow. See AK8963's datasheet, section
      * 6.4.3.6 - Magnetic Sensor Overflow. */
     if ((regs.st2 & 0x08)) {
-        goto fail;
+        return;
     }
 
     raw_field = Vector3f(regs.val[0], regs.val[1], regs.val[2]);
 
     if (is_zero(raw_field.x) && is_zero(raw_field.y) && is_zero(raw_field.z)) {
-        goto fail;
+        return;
     }
 
     _make_factory_sensitivity_adjustment(raw_field);
@@ -263,9 +263,6 @@ bool AP_Compass_AK8963::_update()
         }
         _sem->give();
     }
-
-fail:
-    return true;
 }
 
 /*
diff --git a/libraries/AP_Compass/AP_Compass_AK8963.h b/libraries/AP_Compass/AP_Compass_AK8963.h
index 5a75a56b89..518351ee42 100644
--- a/libraries/AP_Compass/AP_Compass_AK8963.h
+++ b/libraries/AP_Compass/AP_Compass_AK8963.h
@@ -50,7 +50,7 @@ private:
     bool _check_id();
     bool _calibrate();
 
-    bool _update();
+    void _update();
     void _update_timer();
 
     AP_AK8963_BusDriver *_bus;
diff --git a/libraries/AP_Compass/AP_Compass_BMM150.cpp b/libraries/AP_Compass/AP_Compass_BMM150.cpp
index 48194ea2a5..cd919be70b 100644
--- a/libraries/AP_Compass/AP_Compass_BMM150.cpp
+++ b/libraries/AP_Compass/AP_Compass_BMM150.cpp
@@ -190,7 +190,7 @@ bool AP_Compass_BMM150::init()
     set_dev_id(_compass_instance, _dev->get_bus_id());
 
     _dev->register_periodic_callback(MEASURE_TIME_USEC,
-            FUNCTOR_BIND_MEMBER(&AP_Compass_BMM150::_update, bool));
+            FUNCTOR_BIND_MEMBER(&AP_Compass_BMM150::_update, void));
 
     return true;
 
@@ -237,7 +237,7 @@ int16_t AP_Compass_BMM150::_compensate_z(int16_t z, uint32_t rhall)
     return constrain_int32(dividend / divisor, -0x8000, 0x8000);
 }
 
-bool AP_Compass_BMM150::_update()
+void AP_Compass_BMM150::_update()
 {
     const uint32_t time_usec = AP_HAL::micros();
 
@@ -246,7 +246,7 @@ bool AP_Compass_BMM150::_update()
 
     /* Checking data ready status */
     if (!ret || !(data[3] & 0x1)) {
-        return true;
+        return;
     }
 
     const uint16_t rhall = le16toh(data[3] >> 2);
@@ -273,7 +273,7 @@ bool AP_Compass_BMM150::_update()
     correct_field(raw_field, _compass_instance);
 
     if (!_sem->take(HAL_SEMAPHORE_BLOCK_FOREVER)) {
-        return true;
+        return;
     }
     _mag_accum += raw_field;
     _accum_count++;
@@ -282,7 +282,6 @@ bool AP_Compass_BMM150::_update()
         _accum_count = 5;
     }
     _sem->give();
-    return true;
 }
 
 void AP_Compass_BMM150::read()
diff --git a/libraries/AP_Compass/AP_Compass_BMM150.h b/libraries/AP_Compass/AP_Compass_BMM150.h
index de24c6d4da..83b95fad9d 100644
--- a/libraries/AP_Compass/AP_Compass_BMM150.h
+++ b/libraries/AP_Compass/AP_Compass_BMM150.h
@@ -41,7 +41,7 @@ private:
      * Device periodic callback to read data from the sensor.
      */
     bool init();
-    bool _update();
+    void _update();
     bool _load_trim_values();
     int16_t _compensate_xy(int16_t xy, uint32_t rhall, int32_t txy1, int32_t txy2);
     int16_t _compensate_z(int16_t z, uint32_t rhall);
diff --git a/libraries/AP_Compass/AP_Compass_HMC5843.cpp b/libraries/AP_Compass/AP_Compass_HMC5843.cpp
index 5cff49b5c6..a151e98728 100644
--- a/libraries/AP_Compass/AP_Compass_HMC5843.cpp
+++ b/libraries/AP_Compass/AP_Compass_HMC5843.cpp
@@ -209,7 +209,7 @@ bool AP_Compass_HMC5843::init()
 
     // read from sensor at 75Hz
     _bus->register_periodic_callback(13333,
-                                     FUNCTOR_BIND_MEMBER(&AP_Compass_HMC5843::_timer, bool));
+                                     FUNCTOR_BIND_MEMBER(&AP_Compass_HMC5843::_timer, void));
 
     hal.console->printf("HMC5843 found on bus 0x%x\n", _bus->get_bus_id());
     
@@ -225,7 +225,7 @@ errout:
  *
  * bus semaphore has been taken already by HAL
  */
-bool AP_Compass_HMC5843::_timer()
+void AP_Compass_HMC5843::_timer()
 {
     bool result = _read_sample();
 
@@ -233,7 +233,7 @@ bool AP_Compass_HMC5843::_timer()
     _take_sample();
     
     if (!result) {
-        return true;
+        return;
     }
 
     uint32_t tnow = AP_HAL::micros();    
@@ -274,8 +274,6 @@ bool AP_Compass_HMC5843::_timer()
         }
         _sem->give();
     }
-    
-    return true;
 }
 
 /*
diff --git a/libraries/AP_Compass/AP_Compass_HMC5843.h b/libraries/AP_Compass/AP_Compass_HMC5843.h
index 3197bb0b43..11c4cca793 100644
--- a/libraries/AP_Compass/AP_Compass_HMC5843.h
+++ b/libraries/AP_Compass/AP_Compass_HMC5843.h
@@ -39,8 +39,8 @@ private:
     bool _calibrate();
     bool _setup_sampling_mode();
 
-    bool _timer();
-    
+    void _timer();
+
     /* Read a single sample */
     bool _read_sample();
 
diff --git a/libraries/AP_Compass/AP_Compass_IST8310.cpp b/libraries/AP_Compass/AP_Compass_IST8310.cpp
index 264d95e51b..2bd63b567b 100644
--- a/libraries/AP_Compass/AP_Compass_IST8310.cpp
+++ b/libraries/AP_Compass/AP_Compass_IST8310.cpp
@@ -111,7 +111,7 @@ bool AP_Compass_IST8310::init()
     set_dev_id(_instance, _dev->get_bus_id());
 
     _dev->register_periodic_callback(10 * USEC_PER_MSEC,
-                                     FUNCTOR_BIND_MEMBER(&AP_Compass_IST8310::timer, bool));
+                                     FUNCTOR_BIND_MEMBER(&AP_Compass_IST8310::timer, void));
 
     return true;
 
@@ -126,9 +126,8 @@ void AP_Compass_IST8310::start_conversion()
             SINGLE_MEASUREMENT_MODE);
 }
 
-bool AP_Compass_IST8310::timer()
+void AP_Compass_IST8310::timer()
 {
-
     bool ret = false;
 
     struct PACKED {
@@ -142,14 +141,14 @@ bool AP_Compass_IST8310::timer()
     ret = _dev->read_registers(STAT1_REG, (uint8_t *) &buffer, sizeof(buffer));
     if (!ret) {
         /* We're going to be back on the next iteration either way */
-        return true;
+        return;
     }
 
     auto status = buffer.status;
 
     if (!(status & 0x01)) {
         /* We're not ready yet */
-       return true;
+       return;
     }
 
     auto x = static_cast<int16_t>(le16toh(buffer.rx));
@@ -175,8 +174,6 @@ bool AP_Compass_IST8310::timer()
     }
 
     start_conversion();
-
-    return true;
 }
 
 void AP_Compass_IST8310::read()
diff --git a/libraries/AP_Compass/AP_Compass_IST8310.h b/libraries/AP_Compass/AP_Compass_IST8310.h
index 7927096475..2ee0cf0c5c 100644
--- a/libraries/AP_Compass/AP_Compass_IST8310.h
+++ b/libraries/AP_Compass/AP_Compass_IST8310.h
@@ -41,7 +41,7 @@ private:
                        AP_HAL::OwnPtr<AP_HAL::Device> dev,
                        enum Rotation rotation);
 
-    bool timer();
+    void timer();
     bool init();
     void start_conversion();
 
diff --git a/libraries/AP_Compass/AP_Compass_LIS3MDL.cpp b/libraries/AP_Compass/AP_Compass_LIS3MDL.cpp
index 12c7381364..15d6ef6ef6 100644
--- a/libraries/AP_Compass/AP_Compass_LIS3MDL.cpp
+++ b/libraries/AP_Compass/AP_Compass_LIS3MDL.cpp
@@ -125,7 +125,7 @@ bool AP_Compass_LIS3MDL::init()
 
     // call timer() at 155Hz
     dev->register_periodic_callback(1000000U/155U,
-                                    FUNCTOR_BIND_MEMBER(&AP_Compass_LIS3MDL::timer, bool));
+                                    FUNCTOR_BIND_MEMBER(&AP_Compass_LIS3MDL::timer, void));
 
     return true;
 
@@ -134,7 +134,7 @@ fail:
     return false;
 }
 
-bool AP_Compass_LIS3MDL::timer()
+void AP_Compass_LIS3MDL::timer()
 {
     struct PACKED {
         int16_t magx;
@@ -177,7 +177,6 @@ bool AP_Compass_LIS3MDL::timer()
 
 check_registers:
     dev->check_next_register();
-    return true;
 }
 
 void AP_Compass_LIS3MDL::read()
diff --git a/libraries/AP_Compass/AP_Compass_LIS3MDL.h b/libraries/AP_Compass/AP_Compass_LIS3MDL.h
index 18e5027704..dc3255e41a 100644
--- a/libraries/AP_Compass/AP_Compass_LIS3MDL.h
+++ b/libraries/AP_Compass/AP_Compass_LIS3MDL.h
@@ -50,7 +50,7 @@ private:
      * Device periodic callback to read data from the sensor.
      */
     bool init();
-    bool timer();
+    void timer();
 
     uint8_t compass_instance;
     Vector3f accum;
diff --git a/libraries/AP_Compass/AP_Compass_LSM303D.cpp b/libraries/AP_Compass/AP_Compass_LSM303D.cpp
index a5c306a00f..a3e6e10420 100644
--- a/libraries/AP_Compass/AP_Compass_LSM303D.cpp
+++ b/libraries/AP_Compass/AP_Compass_LSM303D.cpp
@@ -284,7 +284,7 @@ bool AP_Compass_LSM303D::init(enum Rotation rotation)
 #endif
 
     // read at 100Hz
-    _dev->register_periodic_callback(10000, FUNCTOR_BIND_MEMBER(&AP_Compass_LSM303D::_update, bool));
+    _dev->register_periodic_callback(10000, FUNCTOR_BIND_MEMBER(&AP_Compass_LSM303D::_update, void));
 
     return true;
 }
@@ -343,10 +343,10 @@ fail_whoami:
     return false;
 }
 
-bool AP_Compass_LSM303D::_update()
+void AP_Compass_LSM303D::_update()
 {
     if (!_read_sample()) {
-        return true;
+        return;
     }
 
     Vector3f raw_field = Vector3f(_mag_x, _mag_y, _mag_z) * _mag_range_scale;
@@ -373,7 +373,6 @@ bool AP_Compass_LSM303D::_update()
         }
         _sem->give();
     }
-    return true;
 }
 
 // Read Sensor data
diff --git a/libraries/AP_Compass/AP_Compass_LSM303D.h b/libraries/AP_Compass/AP_Compass_LSM303D.h
index beb6934175..dcc263ba76 100644
--- a/libraries/AP_Compass/AP_Compass_LSM303D.h
+++ b/libraries/AP_Compass/AP_Compass_LSM303D.h
@@ -34,7 +34,7 @@ private:
 
     bool _data_ready();
     bool _hardware_init();
-    bool _update();
+    void _update();
     void _disable_i2c();
     bool _mag_set_range(uint8_t max_ga);
     bool _mag_set_samplerate(uint16_t frequency);
diff --git a/libraries/AP_Compass/AP_Compass_LSM9DS1.cpp b/libraries/AP_Compass/AP_Compass_LSM9DS1.cpp
index fbc5e2e915..be03506aae 100644
--- a/libraries/AP_Compass/AP_Compass_LSM9DS1.cpp
+++ b/libraries/AP_Compass/AP_Compass_LSM9DS1.cpp
@@ -113,7 +113,7 @@ bool AP_Compass_LSM9DS1::init()
     _dev->set_device_type(DEVTYPE_LSM9DS1);
     set_dev_id(_compass_instance, _dev->get_bus_id());
 
-    _dev->register_periodic_callback(10000, FUNCTOR_BIND_MEMBER(&AP_Compass_LSM9DS1::_update, bool));
+    _dev->register_periodic_callback(10000, FUNCTOR_BIND_MEMBER(&AP_Compass_LSM9DS1::_update, void));
 
     bus_sem->give();
 
@@ -137,24 +137,24 @@ void AP_Compass_LSM9DS1::_dump_registers()
     hal.console->println();
 }
 
-bool AP_Compass_LSM9DS1::_update(void)
+void AP_Compass_LSM9DS1::_update(void)
 {
     struct sample_regs regs;
     Vector3f raw_field;
     uint32_t time_us = AP_HAL::micros();
 
     if (!_block_read(LSM9DS1M_STATUS_REG_M, (uint8_t *) &regs, sizeof(regs))) {
-        goto fail;
+        return;
     }
 
     if (regs.status & 0x80) {
-        goto fail;
+        return;
     }
 
     raw_field = Vector3f(regs.val[0], regs.val[1], regs.val[2]);
 
     if (is_zero(raw_field.x) && is_zero(raw_field.y) && is_zero(raw_field.z)) {
-        goto fail;
+        return;
     }
 
     raw_field *= _scaling;
@@ -181,9 +181,6 @@ bool AP_Compass_LSM9DS1::_update(void)
         }
         _sem->give();
     }
-
-fail:
-    return true;
 }
 
 void AP_Compass_LSM9DS1::read()
diff --git a/libraries/AP_Compass/AP_Compass_LSM9DS1.h b/libraries/AP_Compass/AP_Compass_LSM9DS1.h
index 4a68b06445..db860252f5 100644
--- a/libraries/AP_Compass/AP_Compass_LSM9DS1.h
+++ b/libraries/AP_Compass/AP_Compass_LSM9DS1.h
@@ -28,7 +28,7 @@ private:
     bool _check_id(void);
     bool _configure(void);
     bool _set_scale(void);
-    bool _update(void);
+    void _update(void);
 
     uint8_t _register_read(uint8_t reg);
     void _register_write(uint8_t reg, uint8_t val);
diff --git a/libraries/AP_HAL/Device.h b/libraries/AP_HAL/Device.h
index 8121be0f2d..8a512849bf 100644
--- a/libraries/AP_HAL/Device.h
+++ b/libraries/AP_HAL/Device.h
@@ -38,7 +38,7 @@ public:
         SPEED_LOW,
     };
 
-    FUNCTOR_TYPEDEF(PeriodicCb, bool);
+    FUNCTOR_TYPEDEF(PeriodicCb, void);
     typedef void* PeriodicHandle;
 
     Device(enum BusType type)
diff --git a/libraries/AP_HAL_Linux/AnalogIn_Raspilot.cpp b/libraries/AP_HAL_Linux/AnalogIn_Raspilot.cpp
index bf50bb3a36..a24701a6eb 100644
--- a/libraries/AP_HAL_Linux/AnalogIn_Raspilot.cpp
+++ b/libraries/AP_HAL_Linux/AnalogIn_Raspilot.cpp
@@ -81,10 +81,10 @@ void AnalogIn_Raspilot::init()
         return;
     }
 
-    _dev->register_periodic_callback(100000, FUNCTOR_BIND_MEMBER(&AnalogIn_Raspilot::_update, bool));
+    _dev->register_periodic_callback(100000, FUNCTOR_BIND_MEMBER(&AnalogIn_Raspilot::_update, void));
 }
 
-bool AnalogIn_Raspilot::_update()
+void AnalogIn_Raspilot::_update()
 {
     struct IOPacket tx = { }, rx = { };
     uint16_t count = RASPILOT_ADC_MAX_CHANNELS;
@@ -120,5 +120,4 @@ bool AnalogIn_Raspilot::_update()
             }
         }
     }
-    return true;
 }
diff --git a/libraries/AP_HAL_Linux/AnalogIn_Raspilot.h b/libraries/AP_HAL_Linux/AnalogIn_Raspilot.h
index db48ff469e..5ee582fdf7 100644
--- a/libraries/AP_HAL_Linux/AnalogIn_Raspilot.h
+++ b/libraries/AP_HAL_Linux/AnalogIn_Raspilot.h
@@ -35,7 +35,7 @@ public:
     float board_voltage(void);
 
 protected:
-    bool _update();
+    void _update();
 
     AP_HAL::AnalogSource *_vcc_pin_analog_source;
     AnalogSource_Raspilot *_channels[RASPILOT_ADC_MAX_CHANNELS];
diff --git a/libraries/AP_HAL_Linux/PollerThread.cpp b/libraries/AP_HAL_Linux/PollerThread.cpp
index 8b8302b626..ce505f1e6a 100644
--- a/libraries/AP_HAL_Linux/PollerThread.cpp
+++ b/libraries/AP_HAL_Linux/PollerThread.cpp
@@ -41,9 +41,7 @@ void TimerPollable::on_can_read()
         _wrapper->start_cb();
     }
 
-    if (!_cb()) {
-        _removeme = true;
-    }
+    _cb();
 
     if (_wrapper) {
         _wrapper->end_cb();
diff --git a/libraries/AP_HAL_Linux/RCInput_Raspilot.cpp b/libraries/AP_HAL_Linux/RCInput_Raspilot.cpp
index edffcab341..1d5ab68f0b 100644
--- a/libraries/AP_HAL_Linux/RCInput_Raspilot.cpp
+++ b/libraries/AP_HAL_Linux/RCInput_Raspilot.cpp
@@ -24,10 +24,10 @@ void RCInput_Raspilot::init()
     _dev = hal.spi->get_device("raspio");
 
     // start the timer process to read samples
-    _dev->register_periodic_callback(10000, FUNCTOR_BIND_MEMBER(&RCInput_Raspilot::_poll_data, bool));
+    _dev->register_periodic_callback(10000, FUNCTOR_BIND_MEMBER(&RCInput_Raspilot::_poll_data, void));
 }
 
-bool RCInput_Raspilot::_poll_data(void)
+void RCInput_Raspilot::_poll_data(void)
 {
     struct IOPacket _dma_packet_tx, _dma_packet_rx;
     uint16_t count = LINUX_RC_INPUT_NUM_CHANNELS;
@@ -52,8 +52,6 @@ bool RCInput_Raspilot::_poll_data(void)
     if ( rc_ok && (rx_crc == crc_packet(&_dma_packet_rx)) ) {
       _update_periods(&_dma_packet_rx.regs[6], (uint8_t)num_values);
     }
-
-    return true;
 }
 
 #endif // CONFIG_HAL_BOARD_SUBTYPE
diff --git a/libraries/AP_HAL_Linux/RCInput_Raspilot.h b/libraries/AP_HAL_Linux/RCInput_Raspilot.h
index 16fb077f56..fc9a8670ea 100644
--- a/libraries/AP_HAL_Linux/RCInput_Raspilot.h
+++ b/libraries/AP_HAL_Linux/RCInput_Raspilot.h
@@ -15,7 +15,7 @@ public:
 private:
     AP_HAL::OwnPtr<AP_HAL::SPIDevice> _dev;
 
-    bool _poll_data(void);
+    void _poll_data(void);
 };
 
 }
diff --git a/libraries/AP_HAL_Linux/RCOutput_Raspilot.cpp b/libraries/AP_HAL_Linux/RCOutput_Raspilot.cpp
index dea9c68b54..223217ba78 100644
--- a/libraries/AP_HAL_Linux/RCOutput_Raspilot.cpp
+++ b/libraries/AP_HAL_Linux/RCOutput_Raspilot.cpp
@@ -27,7 +27,7 @@ void RCOutput_Raspilot::init()
 {
     _dev = hal.spi->get_device("raspio");
 
-    _dev->register_periodic_callback(10000, FUNCTOR_BIND_MEMBER(&RCOutput_Raspilot::_update, bool));
+    _dev->register_periodic_callback(10000, FUNCTOR_BIND_MEMBER(&RCOutput_Raspilot::_update, void));
 }
 
 void RCOutput_Raspilot::set_freq(uint32_t chmask, uint16_t freq_hz)
@@ -74,12 +74,12 @@ void RCOutput_Raspilot::read(uint16_t* period_us, uint8_t len)
         period_us[i] = read(0 + i);
 }
 
-bool RCOutput_Raspilot::_update(void)
+void RCOutput_Raspilot::_update(void)
 {
     int i;
 
     if (_corked) {
-        return true;
+        return;
     }
 
     if (_new_frequency) {
@@ -129,7 +129,6 @@ bool RCOutput_Raspilot::_update(void)
     _dma_packet_tx.crc = crc_packet(&_dma_packet_tx);
     _dev->transfer((uint8_t *)&_dma_packet_tx, sizeof(_dma_packet_tx),
                    (uint8_t *)&_dma_packet_rx, sizeof(_dma_packet_rx));
-    return true;
 }
 
 void RCOutput_Raspilot::cork(void)
diff --git a/libraries/AP_HAL_Linux/RCOutput_Raspilot.h b/libraries/AP_HAL_Linux/RCOutput_Raspilot.h
index 179ae62199..e8529ea918 100644
--- a/libraries/AP_HAL_Linux/RCOutput_Raspilot.h
+++ b/libraries/AP_HAL_Linux/RCOutput_Raspilot.h
@@ -20,7 +20,7 @@ public:
 
 private:
     void reset();
-    bool _update(void);
+    void _update(void);
 
     AP_HAL::OwnPtr<AP_HAL::SPIDevice> _dev;
 
diff --git a/libraries/AP_HAL_Linux/RPIOUARTDriver.cpp b/libraries/AP_HAL_Linux/RPIOUARTDriver.cpp
index f44fceca42..d80b566558 100644
--- a/libraries/AP_HAL_Linux/RPIOUARTDriver.cpp
+++ b/libraries/AP_HAL_Linux/RPIOUARTDriver.cpp
@@ -66,7 +66,7 @@ void RPIOUARTDriver::begin(uint32_t b, uint16_t rxS, uint16_t txS)
     if (!_registered_callback) {
         _dev = hal.spi->get_device("raspio");
         _registered_callback = true;
-        _dev->register_periodic_callback(100000, FUNCTOR_BIND_MEMBER(&RPIOUARTDriver::_bus_timer, bool));
+        _dev->register_periodic_callback(100000, FUNCTOR_BIND_MEMBER(&RPIOUARTDriver::_bus_timer, void));
     }
 
     /* set baudrate */
@@ -105,7 +105,7 @@ void RPIOUARTDriver::_timer_tick(void)
     }
 }
 
-bool RPIOUARTDriver::_bus_timer(void)
+void RPIOUARTDriver::_bus_timer(void)
 {
     /* set the baudrate of raspilotio */
     if (_need_set_baud) {
@@ -129,7 +129,7 @@ bool RPIOUARTDriver::_bus_timer(void)
     /* finish set */
 
     if (!_initialised) {
-        return true;
+        return;
     }
 
     _in_timer = true;
@@ -172,6 +172,4 @@ bool RPIOUARTDriver::_bus_timer(void)
     }
 
     _in_timer = false;
-
-    return true;
 }
diff --git a/libraries/AP_HAL_Linux/RPIOUARTDriver.h b/libraries/AP_HAL_Linux/RPIOUARTDriver.h
index 9a4df0f4d2..e1b119bf7b 100644
--- a/libraries/AP_HAL_Linux/RPIOUARTDriver.h
+++ b/libraries/AP_HAL_Linux/RPIOUARTDriver.h
@@ -26,7 +26,7 @@ protected:
 private:
     bool _in_timer;
 
-    bool _bus_timer(void);
+    void _bus_timer(void);
 
     AP_HAL::OwnPtr<AP_HAL::SPIDevice> _dev;
 
diff --git a/libraries/AP_IRLock/AP_IRLock_I2C.cpp b/libraries/AP_IRLock/AP_IRLock_I2C.cpp
index eea4776b6d..46f1ab1d33 100644
--- a/libraries/AP_IRLock/AP_IRLock_I2C.cpp
+++ b/libraries/AP_IRLock/AP_IRLock_I2C.cpp
@@ -44,7 +44,7 @@ void AP_IRLock_I2C::init()
     // read at 50Hz
     printf("Starting IRLock on I2C\n");
 
-    dev->register_periodic_callback(20000, FUNCTOR_BIND_MEMBER(&AP_IRLock_I2C::read_frames, bool));
+    dev->register_periodic_callback(20000, FUNCTOR_BIND_MEMBER(&AP_IRLock_I2C::read_frames, void));
 }
 
 /*
@@ -108,15 +108,15 @@ bool AP_IRLock_I2C::read_block(struct frame &irframe)
     return true;
 }
 
-bool AP_IRLock_I2C::read_frames(void)
+void AP_IRLock_I2C::read_frames(void)
 {
     if (!sync_frame_start()) {
-        return true;
+        return;
     }
     struct frame irframe;
     
     if (!read_block(irframe)) {
-        return true;
+        return;
     }
 
     int16_t corner1_pix_x = irframe.pixel_x - irframe.pixel_size_x/2;
@@ -148,8 +148,6 @@ bool AP_IRLock_I2C::read_frames(void)
                _target_info.size_x, _target_info.size_y);
     }
 #endif
-
-    return true;
 }
 
 // retrieve latest sensor data - returns true if new data is available
diff --git a/libraries/AP_IRLock/AP_IRLock_I2C.h b/libraries/AP_IRLock/AP_IRLock_I2C.h
index dcb17004ac..80238a41df 100644
--- a/libraries/AP_IRLock/AP_IRLock_I2C.h
+++ b/libraries/AP_IRLock/AP_IRLock_I2C.h
@@ -31,7 +31,7 @@ private:
 
     bool sync_frame_start(void);
     bool read_block(struct frame &irframe);
-    bool read_frames(void);
+    void read_frames(void);
 
     void pixel_to_1M_plane(float pix_x, float pix_y, float &ret_x, float &ret_y);
 
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_BMI160.cpp b/libraries/AP_InertialSensor/AP_InertialSensor_BMI160.cpp
index f5305c0cc2..94ee571b11 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_BMI160.cpp
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_BMI160.cpp
@@ -185,7 +185,7 @@ void AP_InertialSensor_BMI160::start()
 
     /* Call _poll_data() at 1kHz */
     _dev->register_periodic_callback(1000,
-        FUNCTOR_BIND_MEMBER(&AP_InertialSensor_BMI160::_poll_data, bool));
+        FUNCTOR_BIND_MEMBER(&AP_InertialSensor_BMI160::_poll_data, void));
 }
 
 bool AP_InertialSensor_BMI160::update()
@@ -417,10 +417,9 @@ read_fifo_end:
     }
 }
 
-bool AP_InertialSensor_BMI160::_poll_data()
+void AP_InertialSensor_BMI160::_poll_data()
 {
     _read_fifo();
-    return true;
 }
 
 bool AP_InertialSensor_BMI160::_hardware_init()
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_BMI160.h b/libraries/AP_InertialSensor/AP_InertialSensor_BMI160.h
index 240731b72a..332910f39f 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_BMI160.h
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_BMI160.h
@@ -98,7 +98,7 @@ private:
     /**
      * Device periodic callback to read data from the sensors.
      */
-    bool _poll_data();
+    void _poll_data();
 
     /**
      * Read samples from fifo.
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_Invensense.cpp b/libraries/AP_InertialSensor/AP_InertialSensor_Invensense.cpp
index 1e4ff3a818..2f8376d31c 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_Invensense.cpp
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_Invensense.cpp
@@ -463,7 +463,7 @@ void AP_InertialSensor_Invensense::start()
     }
 
     // start the timer process to read samples
-    _dev->register_periodic_callback(1000, FUNCTOR_BIND_MEMBER(&AP_InertialSensor_Invensense::_poll_data, bool));
+    _dev->register_periodic_callback(1000, FUNCTOR_BIND_MEMBER(&AP_InertialSensor_Invensense::_poll_data, void));
 }
 
 
@@ -519,10 +519,9 @@ bool AP_InertialSensor_Invensense::_data_ready()
 /*
  * Timer process to poll for new data from the Invensense. Called from bus thread with semaphore held
  */
-bool AP_InertialSensor_Invensense::_poll_data()
+void AP_InertialSensor_Invensense::_poll_data()
 {
     _read_fifo();
-    return true;
 }
 
 bool AP_InertialSensor_Invensense::_accumulate(uint8_t *samples, uint8_t n_samples)
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_Invensense.h b/libraries/AP_InertialSensor/AP_InertialSensor_Invensense.h
index 4615946050..54b36342dd 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_Invensense.h
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_Invensense.h
@@ -83,7 +83,7 @@ private:
     bool _data_ready();
 
     /* Poll for new data (non-blocking) */
-    bool _poll_data();
+    void _poll_data();
 
     /* Read and write functions taking the differences between buses into
      * account */
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_L3G4200D.cpp b/libraries/AP_InertialSensor/AP_InertialSensor_L3G4200D.cpp
index 6dfe709ca0..31f316139d 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_L3G4200D.cpp
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_L3G4200D.cpp
@@ -211,7 +211,7 @@ void AP_InertialSensor_L3G4200D::start(void)
     _accel_instance = _imu.register_accel(800, _dev->get_bus_id_devtype(DEVTYPE_L3G4200D));
 
     // start the timer process to read samples
-    _dev->register_periodic_callback(1250, FUNCTOR_BIND_MEMBER(&AP_InertialSensor_L3G4200D::_accumulate, bool));
+    _dev->register_periodic_callback(1250, FUNCTOR_BIND_MEMBER(&AP_InertialSensor_L3G4200D::_accumulate, void));
 }
 
 /*
@@ -226,7 +226,7 @@ bool AP_InertialSensor_L3G4200D::update(void)
 }
 
 // Accumulate values from accels and gyros
-bool AP_InertialSensor_L3G4200D::_accumulate(void)
+void AP_InertialSensor_L3G4200D::_accumulate(void)
 {
     uint8_t num_samples_available;
     uint8_t fifo_status = 0;
@@ -279,8 +279,7 @@ bool AP_InertialSensor_L3G4200D::_accumulate(void)
                 _notify_new_accel_raw_sample(_accel_instance, accel);
             }
         }
-    }
-    return true;
+    } 
 }
 
 #endif
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_L3G4200D.h b/libraries/AP_InertialSensor/AP_InertialSensor_L3G4200D.h
index f3728e0288..02da026176 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_L3G4200D.h
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_L3G4200D.h
@@ -28,7 +28,7 @@ public:
 
 private:
     bool _init_sensor();
-    bool _accumulate();
+    void _accumulate();
 
     AP_HAL::OwnPtr<AP_HAL::I2CDevice> _dev;
 
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_LSM9DS0.cpp b/libraries/AP_InertialSensor/AP_InertialSensor_LSM9DS0.cpp
index 5a17fb4d61..700acd8881 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_LSM9DS0.cpp
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_LSM9DS0.cpp
@@ -528,7 +528,7 @@ void AP_InertialSensor_LSM9DS0::start(void)
     _set_accel_max_abs_offset(_accel_instance, 5.0f);
 
     /* start the timer process to read samples */
-    _dev_gyro->register_periodic_callback(1000, FUNCTOR_BIND_MEMBER(&AP_InertialSensor_LSM9DS0::_poll_data, bool));
+    _dev_gyro->register_periodic_callback(1000, FUNCTOR_BIND_MEMBER(&AP_InertialSensor_LSM9DS0::_poll_data, void));
 }
 
 
@@ -685,7 +685,7 @@ void AP_InertialSensor_LSM9DS0::_set_accel_scale(accel_scale scale)
 /**
  * Timer process to poll for new data from the LSM9DS0.
  */
-bool AP_InertialSensor_LSM9DS0::_poll_data()
+void AP_InertialSensor_LSM9DS0::_poll_data()
 {
     if (_gyro_data_ready()) {
         _read_data_transaction_g();
@@ -701,8 +701,6 @@ bool AP_InertialSensor_LSM9DS0::_poll_data()
     if (!_dev_accel->check_next_register()) {
         _inc_accel_error_count(_accel_instance);
     }
-    
-    return true;
 }
 
 bool AP_InertialSensor_LSM9DS0::_accel_data_ready()
diff --git a/libraries/AP_InertialSensor/AP_InertialSensor_LSM9DS0.h b/libraries/AP_InertialSensor/AP_InertialSensor_LSM9DS0.h
index 49373e1d93..d0f0e758c1 100644
--- a/libraries/AP_InertialSensor/AP_InertialSensor_LSM9DS0.h
+++ b/libraries/AP_InertialSensor/AP_InertialSensor_LSM9DS0.h
@@ -52,7 +52,7 @@ private:
     bool _accel_data_ready();
     bool _gyro_data_ready();
 
-    bool _poll_data();
+    void _poll_data();
 
     bool _init_sensor();
     bool _hardware_init();
diff --git a/libraries/AP_Notify/Display_SSD1306_I2C.cpp b/libraries/AP_Notify/Display_SSD1306_I2C.cpp
index 3b283496aa..7c417a2f08 100644
--- a/libraries/AP_Notify/Display_SSD1306_I2C.cpp
+++ b/libraries/AP_Notify/Display_SSD1306_I2C.cpp
@@ -51,7 +51,7 @@ bool Display_SSD1306_I2C::hw_init()
 
     _need_hw_update = true;
 
-    _dev->register_periodic_callback(20000, FUNCTOR_BIND_MEMBER(&Display_SSD1306_I2C::_timer, bool));
+    _dev->register_periodic_callback(20000, FUNCTOR_BIND_MEMBER(&Display_SSD1306_I2C::_timer, void));
 
     return true;
 }
@@ -62,10 +62,10 @@ bool Display_SSD1306_I2C::hw_update()
     return true;
 }
 
-bool Display_SSD1306_I2C::_timer()
+void Display_SSD1306_I2C::_timer()
 {
     if (!_need_hw_update) {
-        return true;
+        return;
     }
     _need_hw_update = false;
     
@@ -88,8 +88,6 @@ bool Display_SSD1306_I2C::_timer()
         memcpy(&display_buffer.db[0], &_displaybuffer[i * SSD1306_ROWS], SSD1306_ROWS);
         _dev->transfer((uint8_t *)&display_buffer, sizeof(display_buffer), nullptr, 0);
     }
-
-    return true;
 }
 
 bool Display_SSD1306_I2C::set_pixel(uint16_t x, uint16_t y)
diff --git a/libraries/AP_Notify/Display_SSD1306_I2C.h b/libraries/AP_Notify/Display_SSD1306_I2C.h
index 94b8770833..2568af931b 100644
--- a/libraries/AP_Notify/Display_SSD1306_I2C.h
+++ b/libraries/AP_Notify/Display_SSD1306_I2C.h
@@ -18,5 +18,5 @@ private:
     AP_HAL::OwnPtr<AP_HAL::I2CDevice> _dev;
     uint8_t _displaybuffer[SSD1306_ROWS * SSD1306_COLUMNS_PER_PAGE];
     bool _need_hw_update;
-    bool _timer(void);
+    void _timer(void);
 };
diff --git a/libraries/AP_Notify/NavioLED_I2C.cpp b/libraries/AP_Notify/NavioLED_I2C.cpp
index 3863f855e9..0c4770eae2 100644
--- a/libraries/AP_Notify/NavioLED_I2C.cpp
+++ b/libraries/AP_Notify/NavioLED_I2C.cpp
@@ -32,7 +32,7 @@ bool NavioLED_I2C::hw_init()
         return false;
     }
 
-    _dev->register_periodic_callback(20000, FUNCTOR_BIND_MEMBER(&NavioLED_I2C::_timer, bool));
+    _dev->register_periodic_callback(20000, FUNCTOR_BIND_MEMBER(&NavioLED_I2C::_timer, void));
 
     return true;
 }
@@ -47,10 +47,10 @@ bool NavioLED_I2C::hw_set_rgb(uint8_t red, uint8_t green, uint8_t blue)
     return true;
 }
 
-bool NavioLED_I2C::_timer(void)
+void NavioLED_I2C::_timer(void)
 {
     if (!_need_update) {
-        return true;
+        return;
     }
     _need_update = false;
     
@@ -73,6 +73,4 @@ bool NavioLED_I2C::_timer(void)
 			     0x00, 0x00, red_channel_lsb, red_channel_msb};
 
     _dev->transfer(transaction, sizeof(transaction), nullptr, 0);
-    
-    return true;
 }
diff --git a/libraries/AP_Notify/NavioLED_I2C.h b/libraries/AP_Notify/NavioLED_I2C.h
index ab57895e77..ca3f9662e6 100644
--- a/libraries/AP_Notify/NavioLED_I2C.h
+++ b/libraries/AP_Notify/NavioLED_I2C.h
@@ -27,7 +27,7 @@ protected:
 
 private:
     AP_HAL::OwnPtr<AP_HAL::I2CDevice> _dev;
-    bool _timer(void);
+    void _timer(void);
     struct {
         uint8_t r, g, b;
     } rgb;
diff --git a/libraries/AP_Notify/ToshibaLED_I2C.cpp b/libraries/AP_Notify/ToshibaLED_I2C.cpp
index 6558178d86..0a20a6fca1 100644
--- a/libraries/AP_Notify/ToshibaLED_I2C.cpp
+++ b/libraries/AP_Notify/ToshibaLED_I2C.cpp
@@ -53,7 +53,7 @@ bool ToshibaLED_I2C::hw_init()
     // give back i2c semaphore
     _dev->get_semaphore()->give();
 
-    _dev->register_periodic_callback(20000, FUNCTOR_BIND_MEMBER(&ToshibaLED_I2C::_timer, bool));
+    _dev->register_periodic_callback(20000, FUNCTOR_BIND_MEMBER(&ToshibaLED_I2C::_timer, void));
     
     return ret;
 }
@@ -65,17 +65,16 @@ bool ToshibaLED_I2C::hw_set_rgb(uint8_t red, uint8_t green, uint8_t blue)
     return true;
 }
 
-bool ToshibaLED_I2C::_timer(void)
+void ToshibaLED_I2C::_timer(void)
 {
     if (!_need_update) {
-        return true;
+        return;
     }
     _need_update = false;
-    
+
     /* 4-bit for each color */
     uint8_t val[4] = { TOSHIBA_LED_PWM0, (uint8_t)(rgb.b >> 4),
                        (uint8_t)(rgb.g / 16), (uint8_t)(rgb.r / 16) };
 
     _dev->transfer(val, sizeof(val), nullptr, 0);
-    return true;
 }
diff --git a/libraries/AP_Notify/ToshibaLED_I2C.h b/libraries/AP_Notify/ToshibaLED_I2C.h
index aa62f95387..ecfe3dd911 100644
--- a/libraries/AP_Notify/ToshibaLED_I2C.h
+++ b/libraries/AP_Notify/ToshibaLED_I2C.h
@@ -27,7 +27,7 @@ public:
 
 private:
     AP_HAL::OwnPtr<AP_HAL::I2CDevice> _dev;
-    bool _timer(void);
+    void _timer(void);
     bool _need_update;
     struct {
         uint8_t r, g, b;
diff --git a/libraries/AP_OpticalFlow/AP_OpticalFlow_PX4Flow.cpp b/libraries/AP_OpticalFlow/AP_OpticalFlow_PX4Flow.cpp
index 2eeb1b0381..1773d21a28 100644
--- a/libraries/AP_OpticalFlow/AP_OpticalFlow_PX4Flow.cpp
+++ b/libraries/AP_OpticalFlow/AP_OpticalFlow_PX4Flow.cpp
@@ -88,7 +88,7 @@ bool AP_OpticalFlow_PX4Flow::setup_sensor(void)
         return false;
     }
     // read at 10Hz
-    dev->register_periodic_callback(100000, FUNCTOR_BIND_MEMBER(&AP_OpticalFlow_PX4Flow::timer, bool));
+    dev->register_periodic_callback(100000, FUNCTOR_BIND_MEMBER(&AP_OpticalFlow_PX4Flow::timer, void));
     return true;
 }
 
@@ -99,11 +99,11 @@ void AP_OpticalFlow_PX4Flow::update(void)
 }
 
 // timer to read sensor
-bool AP_OpticalFlow_PX4Flow::timer(void)
+void AP_OpticalFlow_PX4Flow::timer(void)
 {
     struct i2c_integral_frame frame;
     if (!dev->read_registers(REG_INTEGRAL_FRAME, (uint8_t *)&frame, sizeof(frame))) {
-        return true;
+        return;
     }
     struct OpticalFlow::OpticalFlow_state state {};
     state.device_id = get_bus_id();
@@ -124,6 +124,4 @@ bool AP_OpticalFlow_PX4Flow::timer(void)
     }
 
     _update_frontend(state);
-    
-    return true;
 }
diff --git a/libraries/AP_OpticalFlow/AP_OpticalFlow_PX4Flow.h b/libraries/AP_OpticalFlow/AP_OpticalFlow_PX4Flow.h
index f3a03eeea5..9ab7657dff 100644
--- a/libraries/AP_OpticalFlow/AP_OpticalFlow_PX4Flow.h
+++ b/libraries/AP_OpticalFlow/AP_OpticalFlow_PX4Flow.h
@@ -44,5 +44,5 @@ private:
     // setup sensor
     bool setup_sensor(void);
 
-    bool timer(void);
+    void timer(void);
 };
diff --git a/libraries/AP_OpticalFlow/AP_OpticalFlow_Pixart.cpp b/libraries/AP_OpticalFlow/AP_OpticalFlow_Pixart.cpp
index fc520a863d..6d9e14284a 100644
--- a/libraries/AP_OpticalFlow/AP_OpticalFlow_Pixart.cpp
+++ b/libraries/AP_OpticalFlow/AP_OpticalFlow_Pixart.cpp
@@ -149,8 +149,8 @@ bool AP_OpticalFlow_Pixart::setup_sensor(void)
     _dev->get_semaphore()->give();
 
     integral.last_frame_us = AP_HAL::micros();
-    
-    _dev->register_periodic_callback(2000, FUNCTOR_BIND_MEMBER(&AP_OpticalFlow_Pixart::timer, bool));
+
+    _dev->register_periodic_callback(2000, FUNCTOR_BIND_MEMBER(&AP_OpticalFlow_Pixart::timer, void));
     return true;
 
 failed:
@@ -266,10 +266,10 @@ void AP_OpticalFlow_Pixart::motion_burst(void)
     _dev->set_chip_select(false);
 }
 
-bool AP_OpticalFlow_Pixart::timer(void)
+void AP_OpticalFlow_Pixart::timer(void)
 {
     if (AP_HAL::micros() - last_burst_us < 500) {
-        return true;
+        return;
     }
     motion_burst();
     last_burst_us = AP_HAL::micros();
@@ -301,7 +301,6 @@ bool AP_OpticalFlow_Pixart::timer(void)
         sum_x = sum_y = 0;
     }
 #endif
-    return true;
 }
 
 // update - read latest values from sensor and fill in x,y and totals.
diff --git a/libraries/AP_OpticalFlow/AP_OpticalFlow_Pixart.h b/libraries/AP_OpticalFlow/AP_OpticalFlow_Pixart.h
index 8468a2551e..dd28b60ea4 100644
--- a/libraries/AP_OpticalFlow/AP_OpticalFlow_Pixart.h
+++ b/libraries/AP_OpticalFlow/AP_OpticalFlow_Pixart.h
@@ -62,7 +62,7 @@ private:
     void srom_download(void);
     void load_configuration(void);
 
-    bool timer(void);
+    void timer(void);
     void motion_burst(void);
 
     int32_t sum_x;
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_LightWareI2C.cpp b/libraries/AP_RangeFinder/AP_RangeFinder_LightWareI2C.cpp
index b339ae6f93..df614d8e42 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_LightWareI2C.cpp
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_LightWareI2C.cpp
@@ -64,7 +64,7 @@ void AP_RangeFinder_LightWareI2C::init()
 {
     // call timer() at 20Hz
     _dev->register_periodic_callback(50000,
-                                     FUNCTOR_BIND_MEMBER(&AP_RangeFinder_LightWareI2C::timer, bool));
+                                     FUNCTOR_BIND_MEMBER(&AP_RangeFinder_LightWareI2C::timer, void));
 }
 
 // read - return last value measured by sensor
@@ -94,13 +94,12 @@ void AP_RangeFinder_LightWareI2C::update(void)
     // nothing to do - its all done in the timer()
 }
 
-bool AP_RangeFinder_LightWareI2C::timer(void)
+void AP_RangeFinder_LightWareI2C::timer(void)
 {
     if (get_reading(state.distance_cm)) {
         // update range_valid state based on distance measured
         update_status();
     } else {
         set_status(RangeFinder::RangeFinder_NoData);
-    }    
-    return true;
+    }
 }
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_LightWareI2C.h b/libraries/AP_RangeFinder/AP_RangeFinder_LightWareI2C.h
index 13abe64f20..04b941cf6e 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_LightWareI2C.h
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_LightWareI2C.h
@@ -19,8 +19,8 @@ private:
     AP_RangeFinder_LightWareI2C(RangeFinder &ranger, uint8_t instance, RangeFinder::RangeFinder_State &_state, AP_HAL::OwnPtr<AP_HAL::I2CDevice> dev);
 
     void init();
-    bool timer();
-    
+    void timer();
+
     // get a reading
     bool get_reading(uint16_t &reading_cm);
     AP_HAL::OwnPtr<AP_HAL::I2CDevice> _dev;
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_MaxsonarI2CXL.cpp b/libraries/AP_RangeFinder/AP_RangeFinder_MaxsonarI2CXL.cpp
index 0540e7f3e0..aa71da045c 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_MaxsonarI2CXL.cpp
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_MaxsonarI2CXL.cpp
@@ -90,7 +90,7 @@ bool AP_RangeFinder_MaxsonarI2CXL::_init(void)
     _dev->get_semaphore()->give();
     
     _dev->register_periodic_callback(50000,
-                                     FUNCTOR_BIND_MEMBER(&AP_RangeFinder_MaxsonarI2CXL::_timer, bool));
+                                     FUNCTOR_BIND_MEMBER(&AP_RangeFinder_MaxsonarI2CXL::_timer, void));
     
     return true;
 }
@@ -126,7 +126,7 @@ bool AP_RangeFinder_MaxsonarI2CXL::get_reading(uint16_t &reading_cm)
 /*
   timer called at 20Hz
 */
-bool AP_RangeFinder_MaxsonarI2CXL::_timer(void)
+void AP_RangeFinder_MaxsonarI2CXL::_timer(void)
 {
     uint16_t d;
     if (get_reading(d)) {
@@ -136,9 +136,8 @@ bool AP_RangeFinder_MaxsonarI2CXL::_timer(void)
             _sem->give();
         }
     }
-    return true;
 }
-    
+
 
 /*
    update the state of the sensor
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_MaxsonarI2CXL.h b/libraries/AP_RangeFinder/AP_RangeFinder_MaxsonarI2CXL.h
index f65a0e38c9..304560e821 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_MaxsonarI2CXL.h
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_MaxsonarI2CXL.h
@@ -28,8 +28,8 @@ private:
     AP_RangeFinder_MaxsonarI2CXL(RangeFinder &ranger, uint8_t instance,
                                  RangeFinder::RangeFinder_State &_state);
 
-    bool _init(void);    
-    bool _timer(void);
+    bool _init(void);
+    void _timer(void);
 
     uint16_t distance;
     bool new_distance;
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_PulsedLightLRF.cpp b/libraries/AP_RangeFinder/AP_RangeFinder_PulsedLightLRF.cpp
index 646ad50ec0..e5bb46fb42 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_PulsedLightLRF.cpp
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_PulsedLightLRF.cpp
@@ -71,7 +71,7 @@ AP_RangeFinder_Backend *AP_RangeFinder_PulsedLightLRF::detect(uint8_t bus, Range
 /*
   called at 50Hz
  */
-bool AP_RangeFinder_PulsedLightLRF::timer(void)
+void AP_RangeFinder_PulsedLightLRF::timer(void)
 {
     if (check_reg_counter++ == 10) {
         check_reg_counter = 0;
@@ -110,7 +110,6 @@ bool AP_RangeFinder_PulsedLightLRF::timer(void)
         break;
     }
     }
-    return true;
 }
 
 
@@ -181,7 +180,7 @@ bool AP_RangeFinder_PulsedLightLRF::init(void)
     }
 
     _dev->register_periodic_callback(20000,
-                                     FUNCTOR_BIND_MEMBER(&AP_RangeFinder_PulsedLightLRF::timer, bool));
+                                     FUNCTOR_BIND_MEMBER(&AP_RangeFinder_PulsedLightLRF::timer, void));
     return true;
 }
 
diff --git a/libraries/AP_RangeFinder/AP_RangeFinder_PulsedLightLRF.h b/libraries/AP_RangeFinder/AP_RangeFinder_PulsedLightLRF.h
index a79fbf09fc..f9437d3958 100644
--- a/libraries/AP_RangeFinder/AP_RangeFinder_PulsedLightLRF.h
+++ b/libraries/AP_RangeFinder/AP_RangeFinder_PulsedLightLRF.h
@@ -33,7 +33,7 @@ private:
 
     // start a reading
     bool init(void);
-    bool timer(void);
+    void timer(void);
     bool lidar_transfer(const uint8_t *send, unsigned send_len, uint8_t *recv, unsigned recv_len);
     
     AP_HAL::OwnPtr<AP_HAL::I2CDevice> _dev;