diff --git a/inc/MicroBit.h b/inc/MicroBit.h
index 9694615..fd74fed 100644
--- a/inc/MicroBit.h
+++ b/inc/MicroBit.h
@@ -32,7 +32,11 @@
 #include "MicroBitFiber.h"
 #include "MicroBitMessageBus.h"
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-parameter"
 #include "ble/BLE.h"
+#pragma GCC diagnostic pop
+
 #include "ble/services/DeviceInformationService.h"
 #include "MicroBitDFUService.h"
 #include "MicroBitEventService.h"
@@ -264,7 +268,7 @@ class MicroBit
       * @return A textual description of the currentlt executing micro:bit runtime.
       * TODO: handle overflow case.
       */
-    char *systemVersion();
+    const char *systemVersion();
 
     /**
       * Triggers a microbit panic where an infinite loop will occur swapping between the panicFace and statusCode if provided.
diff --git a/source/CMakeLists.txt b/source/CMakeLists.txt
index 2d9806c..8d16619 100755
--- a/source/CMakeLists.txt
+++ b/source/CMakeLists.txt
@@ -1,7 +1,7 @@
 # This file is no longer auto-generated to make the repository builds with GCC
 # and ARMCC no matter what.
 
-cmake_minimum_required(VERSION 2.8.11)
+cmake_minimum_required(VERSION 2.8.12)
 
 enable_language(ASM)
 
@@ -42,7 +42,7 @@ set(YOTTA_AUTO_MICROBIT-DAL_CPP_FILES
 execute_process(WORKING_DIRECTORY "../../yotta_modules/${PROJECT_NAME}" COMMAND "git" "log" "--pretty=format:%h" "-n" "1" OUTPUT_VARIABLE git_hash)
 execute_process(WORKING_DIRECTORY "../../yotta_modules/${PROJECT_NAME}" COMMAND "git" "rev-parse" "--abbrev-ref" "HEAD" OUTPUT_VARIABLE git_branch OUTPUT_STRIP_TRAILING_WHITESPACE)
 
-if (${git_branch} STREQUAL "master")
+if ("${git_branch}" STREQUAL "master")
     set(MICROBIT_DAL_VERSION_STRING "${YOTTA_MICROBIT_DAL_VERSION_STRING}")
 else()
     set(MICROBIT_DAL_VERSION_STRING "${YOTTA_MICROBIT_DAL_VERSION_STRING}-${git_branch}-g${git_hash}")
@@ -80,3 +80,9 @@ target_link_libraries(microbit-dal
     ble
     ble-nrf51822
 )
+
+if(CMAKE_COMPILER_IS_GNUCC)
+    target_compile_options(mbed-classic PRIVATE "-w")
+    target_compile_options(ble PRIVATE "-w")
+    target_compile_options(ble-nrf51822 PRIVATE "-w")
+endif()
diff --git a/source/ManagedString.cpp b/source/ManagedString.cpp
index 362045a..829b65a 100644
--- a/source/ManagedString.cpp
+++ b/source/ManagedString.cpp
@@ -127,7 +127,7 @@ ManagedString::ManagedString(const ManagedString &s1, const ManagedString &s2)
 ManagedString::ManagedString(const char *str, const int16_t length)
 {
     // Sanity check. Return EmptyString for anything distasteful
-    if (str == NULL || *str == 0 || length > strlen(str))
+    if (str == NULL || *str == 0 || (uint16_t)length > strlen(str)) // XXX length should be unsigned on the interface
     {
         initEmpty();
         return;
diff --git a/source/MicroBit.cpp b/source/MicroBit.cpp
index 9558285..ed8d38d 100644
--- a/source/MicroBit.cpp
+++ b/source/MicroBit.cpp
@@ -33,6 +33,9 @@ microbit_reset()
   */
 void bleDisconnectionCallback(Gap::Handle_t handle, Gap::DisconnectionReason_t reason)
 {
+    (void) handle; /* -Wunused-param */
+    (void) reason; /* -Wunused-param */
+
     uBit.ble->startAdvertising(); 
 }
 
@@ -479,7 +482,7 @@ unsigned long MicroBit::systemTime()
  * @return A textual description of the currentlt executing micro:bit runtime.
  * TODO: handle overflow case.
  */
-char *MicroBit::systemVersion()
+const char *MicroBit::systemVersion()
 {
     return MICROBIT_DAL_VERSION;
 }
diff --git a/source/MicroBitDisplay.cpp b/source/MicroBitDisplay.cpp
index 1cd3bd3..1337071 100644
--- a/source/MicroBitDisplay.cpp
+++ b/source/MicroBitDisplay.cpp
@@ -87,7 +87,7 @@ void MicroBitDisplay::renderFinish()
     //kept inline to reduce overhead
     //clear the old bit pattern for this row.
     //clear port 0 4-7 and retain lower 4 bits
-    nrf_gpio_port_write(NRF_GPIO_PORT_SELECT_PORT0, 0xF0 | nrf_gpio_port_read(NRF_GPIO_PORT_SELECT_PORT0) & 0x0F); 
+    nrf_gpio_port_write(NRF_GPIO_PORT_SELECT_PORT0, 0xF0 | (nrf_gpio_port_read(NRF_GPIO_PORT_SELECT_PORT0) & 0x0F)); 
     
     // clear port 1 8-12 for the current row
     nrf_gpio_port_write(NRF_GPIO_PORT_SELECT_PORT1, strobeBitMsk | 0x1F); 
@@ -132,7 +132,7 @@ void MicroBitDisplay::render()
                     
     //write the new bit pattern
     //set port 0 4-7 and retain lower 4 bits
-    nrf_gpio_port_write(NRF_GPIO_PORT_SELECT_PORT0, ~coldata<<4 & 0xF0 | nrf_gpio_port_read(NRF_GPIO_PORT_SELECT_PORT0) & 0x0F); 
+    nrf_gpio_port_write(NRF_GPIO_PORT_SELECT_PORT0, (~coldata<<4 & 0xF0) | (nrf_gpio_port_read(NRF_GPIO_PORT_SELECT_PORT0) & 0x0F)); 
     
     //set port 1 8-12 for the current row
     nrf_gpio_port_write(NRF_GPIO_PORT_SELECT_PORT1, strobeBitMsk | (~coldata>>4 & 0x1F)); 
@@ -180,7 +180,7 @@ void MicroBitDisplay::renderGreyscale()
     }            
     //write the new bit pattern
     //set port 0 4-7 and retain lower 4 bits
-    nrf_gpio_port_write(NRF_GPIO_PORT_SELECT_PORT0, ~coldata<<4 & 0xF0 | nrf_gpio_port_read(NRF_GPIO_PORT_SELECT_PORT0) & 0x0F); 
+    nrf_gpio_port_write(NRF_GPIO_PORT_SELECT_PORT0, (~coldata<<4 & 0xF0) | (nrf_gpio_port_read(NRF_GPIO_PORT_SELECT_PORT0) & 0x0F)); 
     
     //set port 1 8-12 for the current row
     nrf_gpio_port_write(NRF_GPIO_PORT_SELECT_PORT1, strobeBitMsk | (~coldata>>4 & 0x1F)); 
diff --git a/source/MicroBitFiber.cpp b/source/MicroBitFiber.cpp
index 1ae5111..461da33 100644
--- a/source/MicroBitFiber.cpp
+++ b/source/MicroBitFiber.cpp
@@ -130,8 +130,8 @@ Fiber *getFiberContext()
         if (f == NULL)
             return NULL;
 
-        f->stack_bottom = NULL;
-        f->stack_top = NULL;
+        f->stack_bottom = 0;
+        f->stack_top = 0;
     }    
    
     // Ensure this fiber is in suitable state for reuse. 
@@ -512,7 +512,7 @@ Fiber *__create_fiber(uint32_t ep, uint32_t cp, uint32_t pm, int parameterised)
   */
 Fiber *create_fiber(void (*entry_fn)(void), void (*completion_fn)(void))
 {
-    return __create_fiber((uint32_t) entry_fn, (uint32_t)completion_fn, NULL, 0);
+    return __create_fiber((uint32_t) entry_fn, (uint32_t)completion_fn, 0, 0);
 }
 
 
@@ -535,6 +535,8 @@ Fiber *create_fiber(void (*entry_fn)(void *), void *param, void (*completion_fn)
   */
 void release_fiber(void * param)
 {
+    (void)param; /* -Wunused-parameter */
+
     release_fiber();
 }
 
@@ -688,7 +690,7 @@ void schedule()
         if (oldFiber == idleFiber)
         {
             // Just swap in the new fiber, and discard changes to stack and register context.
-            swap_context(NULL, &currentFiber->tcb, NULL, currentFiber->stack_top);
+            swap_context(NULL, &currentFiber->tcb, 0, currentFiber->stack_top);
         }
         else
         {
diff --git a/source/MicroBitHeapAllocator.cpp b/source/MicroBitHeapAllocator.cpp
index 0db4655..36cf1d0 100644
--- a/source/MicroBitHeapAllocator.cpp
+++ b/source/MicroBitHeapAllocator.cpp
@@ -32,7 +32,7 @@ struct HeapDefinition
 
 // Create the necessary heap definitions.
 // We use two heaps by default: one for SoftDevice reuse, and one to run inside the mbed heap.
-HeapDefinition heap[MICROBIT_HEAP_COUNT] = { NULL }; 
+HeapDefinition heap[MICROBIT_HEAP_COUNT] = { }; 
 
 // Scans the status of the heap definition table, and returns the number of INITIALISED heaps.
 int microbit_active_heaps()
diff --git a/source/MicroBitThermometer.cpp b/source/MicroBitThermometer.cpp
index 8e1df04..23163bd 100644
--- a/source/MicroBitThermometer.cpp
+++ b/source/MicroBitThermometer.cpp
@@ -1,5 +1,22 @@
 #include "MicroBit.h"
+
+/**
+  * Turn off warnings under gcc -Wall
+  * We turn off unused-function for the entire compilation
+  * unit as the compiler can't tell if a function is
+  * unused until the end of the unit.  The macro
+  * expansion for SVCALL() in nrf_soc.h and nrf_srv.h
+  * tries to leave unused-function turned off, but
+  * It might be leaner to add
+  * #pragram GCC system header
+  * as the first line of nrf_soc.h, but that's a different
+  * module ...
+  */
+#pragma GCC diagnostic ignored "-Wunused-function"
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-parameter"
 #include "nrf_soc.h"
+#pragma GCC diagnostic pop
 
 /**
   * Constructor. 
diff --git a/source/ble-services/MicroBitAccelerometerService.cpp b/source/ble-services/MicroBitAccelerometerService.cpp
index 3ab777f..46d299a 100644
--- a/source/ble-services/MicroBitAccelerometerService.cpp
+++ b/source/ble-services/MicroBitAccelerometerService.cpp
@@ -67,6 +67,7 @@ void MicroBitAccelerometerService::onDataWritten(const GattWriteCallbackParams *
   */
 void MicroBitAccelerometerService::accelerometerUpdate(MicroBitEvent e)
 {
+    (void) e; /* -Wunused-parameter */
     if (ble.getGapState().connected)
     {
         accelerometerDataCharacteristicBuffer[0] = uBit.accelerometer.getX();
diff --git a/source/ble-services/MicroBitDFUService.cpp b/source/ble-services/MicroBitDFUService.cpp
index ca7438c..96277fa 100644
--- a/source/ble-services/MicroBitDFUService.cpp
+++ b/source/ble-services/MicroBitDFUService.cpp
@@ -51,6 +51,7 @@ MicroBitDFUService::MicroBitDFUService(BLEDevice &_ble) :
 
 void MicroBitDFUService::onButtonA(MicroBitEvent e)
 {
+    (void) e; /* -Wunused-parameter */
     if (flashCodeRequested)
     {
         releaseFlashCode();
@@ -63,6 +64,7 @@ void MicroBitDFUService::onButtonA(MicroBitEvent e)
 
 void MicroBitDFUService::onButtonB(MicroBitEvent e)
 {
+    (void) e; /* -Wunused-parameter */
     uBit.display.scroll("VERSION: TODO");
     showNameHistogram();
 }
diff --git a/source/ble-services/MicroBitIOPinService.cpp b/source/ble-services/MicroBitIOPinService.cpp
index 38319c7..a48e5cd 100644
--- a/source/ble-services/MicroBitIOPinService.cpp
+++ b/source/ble-services/MicroBitIOPinService.cpp
@@ -138,7 +138,7 @@ void MicroBitIOPinService::onDataWritten(const GattWriteCallbackParams *params)
     if (params->handle == ioPinServiceDataCharacteristic->getValueHandle())
     {
         // We have some pin data to change...
-        int len = params->len;
+        uint16_t len = params->len;
         IOData *data = (IOData *)params->data;
 
         // There may be multiple write operaitons... take each in turn and update the pin values
diff --git a/source/ble-services/MicroBitLEDService.cpp b/source/ble-services/MicroBitLEDService.cpp
index 059ab0b..5295615 100644
--- a/source/ble-services/MicroBitLEDService.cpp
+++ b/source/ble-services/MicroBitLEDService.cpp
@@ -59,7 +59,7 @@ void MicroBitLEDService::onDataWritten(const GattWriteCallbackParams *params)
     {
         for (int y=0; y<params->len; y++)        
             for (int x=0; x<5; x++)        
-                uBit.display.image.setPixelValue(x, y, (data[y] & (0x01 << 4-x)) ? 255 : 0);
+                uBit.display.image.setPixelValue(x, y, (data[y] & (0x01 << (4-x))) ? 255 : 0);
     }
 
     else if (params->handle == textCharacteristicHandle) 
@@ -94,7 +94,7 @@ void MicroBitLEDService::onDataRead(GattReadAuthCallbackParams *params)
             for (int x=0; x<5; x++)        
             {
                 if (uBit.display.image.getPixelValue(x, y))
-                    matrixCharacteristicBuffer[y] |= 0x01 << 4-x;
+                    matrixCharacteristicBuffer[y] |= 0x01 << (4-x);
             }
         }
 
diff --git a/source/ble-services/MicroBitMagnetometerService.cpp b/source/ble-services/MicroBitMagnetometerService.cpp
index 08217ed..3ee4647 100644
--- a/source/ble-services/MicroBitMagnetometerService.cpp
+++ b/source/ble-services/MicroBitMagnetometerService.cpp
@@ -69,6 +69,8 @@ void MicroBitMagnetometerService::onDataWritten(const GattWriteCallbackParams *p
   */
 void MicroBitMagnetometerService::magnetometerUpdate(MicroBitEvent e)
 {
+    (void) e; /* -Wunused-parameter */
+
     if (ble.getGapState().connected)
     {
         magnetometerDataCharacteristicBuffer[0] = uBit.compass.getX();
@@ -90,6 +92,8 @@ void MicroBitMagnetometerService::magnetometerUpdate(MicroBitEvent e)
  */
 void MicroBitMagnetometerService::samplePeriodUpdateNeeded(MicroBitEvent e)
 {
+    (void) e; /* -Wunused-parameter */
+
     // Reconfigure the compass. This might take a while...
     uBit.compass.setPeriod(magnetometerPeriodCharacteristicBuffer);
 
diff --git a/source/ble-services/MicroBitTemperatureService.cpp b/source/ble-services/MicroBitTemperatureService.cpp
index bd2fd9e..0b97cb7 100644
--- a/source/ble-services/MicroBitTemperatureService.cpp
+++ b/source/ble-services/MicroBitTemperatureService.cpp
@@ -47,6 +47,8 @@ MicroBitTemperatureService::MicroBitTemperatureService(BLEDevice &_ble) :
   */
 void MicroBitTemperatureService::temperatureUpdate(MicroBitEvent e)
 {
+    (void) e; /* -Wunused-parameter */
+
     if (ble.getGapState().connected)
     {
         temperatureDataCharacteristicBuffer = uBit.thermometer.getTemperature();