Reworked use of optimisation attributes

17 files changed, 68 insertions, 67 deletions

diff --git a/src/Comms/PanelDueUpdater.cpp b/src/Comms/PanelDueUpdater.cpp
index f6ee6893..23f5ef30 100644
--- a/src/Comms/PanelDueUpdater.cpp
+++ b/src/Comms/PanelDueUpdater.cpp
@@ -249,9 +249,9 @@ void PanelDueUpdater::Spin() noexcept
 				auto auxPort = GetAuxPort();
 				auxPort->SetInterruptCallback(currentInterruptCallbackFn);
 				currentInterruptCallbackFn = nullptr;
-	#if ALLOW_OTHER_AUX
+#if ALLOW_OTHER_AUX
 				serialChannel = NumSerialChannels+1;
-	#endif
+#endif
 				currentBaudRate = 0;
 
 				// Delete all objects we new'd
@@ -300,3 +300,5 @@ UARTClass* PanelDueUpdater::GetAuxPort() noexcept
 #endif
 			&SERIAL_AUX_DEVICE;
 }
+
+// End
diff --git a/src/Comms/PanelDueUpdater.h b/src/Comms/PanelDueUpdater.h
index a75bf20e..6ce72f66 100644
--- a/src/Comms/PanelDueUpdater.h
+++ b/src/Comms/PanelDueUpdater.h
@@ -21,8 +21,8 @@
 
 constexpr size_t RequiredBaudRate = 115200;
 
-constexpr const char * const panelDueCommandEraseAndReset	= "{\"controlCommand\":\"eraseAndReset\"}\n";
-constexpr const char * const panelDueCommandReset 			= "{\"controlCommand\":\"reset\"}\n";
+constexpr const char * panelDueCommandEraseAndReset	= "{\"controlCommand\":\"eraseAndReset\"}\n";
+constexpr const char * panelDueCommandReset 		= "{\"controlCommand\":\"reset\"}\n";
 
 constexpr uint32_t WaitMsAfterEraseAndReset = 1000;			// How long to wait in ms after eraseAndReset
 
diff --git a/src/GCodes/GCodeBuffer/BinaryParser.h b/src/GCodes/GCodeBuffer/BinaryParser.h
index 6948381b..2f480388 100644
--- a/src/GCodes/GCodeBuffer/BinaryParser.h
+++ b/src/GCodes/GCodeBuffer/BinaryParser.h
@@ -27,7 +27,7 @@ public:
 	void Init() noexcept; 											// Set it up to parse another G-code
 	void Put(const uint32_t *data, size_t len) noexcept;			// Add an entire binary code, overwriting any existing content
 	void DecodeCommand() noexcept;									// Print the buffer content in debug mode and prepare for execution
-	bool Seen(char c) noexcept __attribute__((hot));				// Is a character present?
+	bool Seen(char c) noexcept SPEED_CRITICAL;				// Is a character present?
 
 	char GetCommandLetter() const noexcept;
 	bool HasCommandNumber() const noexcept;
@@ -35,8 +35,8 @@ public:
 	int8_t GetCommandFraction() const noexcept;
 	bool ContainsExpression() const noexcept;
 
-	float GetFValue() THROWS(GCodeException) __attribute__((hot));				// Get a float after a key letter
-	int32_t GetIValue() THROWS(GCodeException) __attribute__((hot));			// Get an integer after a key letter
+	float GetFValue() THROWS(GCodeException) SPEED_CRITICAL;				// Get a float after a key letter
+	int32_t GetIValue() THROWS(GCodeException) SPEED_CRITICAL;			// Get an integer after a key letter
 	uint32_t GetUIValue() THROWS(GCodeException);								// Get an unsigned integer value
 	DriverId GetDriverId() THROWS(GCodeException);								// Get a driver ID
 	void GetIPAddress(IPAddress& returnedIp) THROWS(GCodeException);			// Get an IP address quad after a key letter
@@ -46,7 +46,7 @@ public:
 	void GetQuotedString(const StringRef& str) THROWS(GCodeException);			// Get and copy a quoted string
 	void GetPossiblyQuotedString(const StringRef& str, bool allowEmpty = false) THROWS(GCodeException);	// Get and copy a string which may or may not be quoted
 	void GetReducedString(const StringRef& str) THROWS(GCodeException);			// Get and copy a quoted string, removing certain characters
-	void GetFloatArray(float arr[], size_t& length, bool doPad) THROWS(GCodeException) __attribute__((hot)); // Get a colon-separated list of floats after a key letter
+	void GetFloatArray(float arr[], size_t& length, bool doPad) THROWS(GCodeException) SPEED_CRITICAL; // Get a colon-separated list of floats after a key letter
 	void GetIntArray(int32_t arr[], size_t& length, bool doPad) THROWS(GCodeException);		// Get a :-separated list of ints after a key letter
 	void GetUnsignedArray(uint32_t arr[], size_t& length, bool doPad) THROWS(GCodeException);	// Get a :-separated list of unsigned ints after a key letter
 	void GetDriverIdArray(DriverId arr[], size_t& length) THROWS(GCodeException);	// Get a :-separated list of drivers after a key letter
@@ -71,7 +71,7 @@ private:
 	GCodeException ConstructParseException(const char *str, uint32_t param) const noexcept;
 
 	size_t AddPadding(size_t bytesRead) const noexcept { return (bytesRead + 3u) & (~3u); }
-	template<typename T> void GetArray(T arr[], size_t& length, bool doPad) THROWS(GCodeException) __attribute__((hot));
+	template<typename T> void GetArray(T arr[], size_t& length, bool doPad) THROWS(GCodeException) SPEED_CRITICAL;
 	void WriteParameters(const StringRef& s, bool quoteStrings) const noexcept;
 
 	size_t bufferLength;
diff --git a/src/GCodes/GCodeBuffer/GCodeBuffer.h b/src/GCodes/GCodeBuffer/GCodeBuffer.h
index 83d7fb79..99b9ce81 100644
--- a/src/GCodes/GCodeBuffer/GCodeBuffer.h
+++ b/src/GCodes/GCodeBuffer/GCodeBuffer.h
@@ -49,7 +49,7 @@ public:
 	void Init() noexcept;														// Set it up to parse another G-code
 	void Diagnostics(MessageType mtype) noexcept;								// Write some debug info
 
-	bool Put(char c) noexcept __attribute__((hot));								// Add a character to the end
+	bool Put(char c) noexcept SPEED_CRITICAL;								// Add a character to the end
 #if HAS_LINUX_INTERFACE
 	void PutBinary(const uint32_t *data, size_t len) noexcept;					// Add an entire binary G-Code, overwriting any existing content
 #endif
@@ -71,12 +71,12 @@ public:
 	GCodeResult GetLastResult() const noexcept { return lastResult; }
 	void SetLastResult(GCodeResult r) noexcept { lastResult = r; }
 
-	bool Seen(char c) noexcept __attribute__((hot));								// Is a character present?
+	bool Seen(char c) noexcept SPEED_CRITICAL;								// Is a character present?
 	void MustSee(char c) THROWS(GCodeException);									// Test for character present, throw error if not
 
-	float GetFValue() THROWS(GCodeException) __attribute__((hot));					// Get a float after a key letter
+	float GetFValue() THROWS(GCodeException) SPEED_CRITICAL;					// Get a float after a key letter
 	float GetDistance() THROWS(GCodeException);										// Get a distance or coordinate and convert it from inches to mm if necessary
-	int32_t GetIValue() THROWS(GCodeException) __attribute__((hot));				// Get an integer after a key letter
+	int32_t GetIValue() THROWS(GCodeException) SPEED_CRITICAL;				// Get an integer after a key letter
 	int32_t GetLimitedIValue(char c, int32_t minValue, int32_t maxValue) THROWS(GCodeException)
 		post(minValue <= result; result <= maxValue);								// Get an integer after a key letter
 	uint32_t GetUIValue() THROWS(GCodeException);									// Get an unsigned integer value
@@ -92,7 +92,7 @@ public:
 	void GetQuotedString(const StringRef& str) THROWS(GCodeException);				// Get and copy a quoted string
 	void GetPossiblyQuotedString(const StringRef& str) THROWS(GCodeException);		// Get and copy a string which may or may not be quoted
 	void GetReducedString(const StringRef& str) THROWS(GCodeException);				// Get and copy a quoted string, removing certain characters
-	void GetFloatArray(float arr[], size_t& length, bool doPad) THROWS(GCodeException) __attribute__((hot)); // Get a colon-separated list of floats after a key letter
+	void GetFloatArray(float arr[], size_t& length, bool doPad) THROWS(GCodeException) SPEED_CRITICAL; // Get a colon-separated list of floats after a key letter
 	void GetIntArray(int32_t arr[], size_t& length, bool doPad) THROWS(GCodeException);		// Get a :-separated list of ints after a key letter
 	void GetUnsignedArray(uint32_t arr[], size_t& length, bool doPad) THROWS(GCodeException);	// Get a :-separated list of unsigned ints after a key letter
 	void GetDriverIdArray(DriverId arr[], size_t& length) THROWS(GCodeException);	// Get a :-separated list of drivers after a key letter
diff --git a/src/GCodes/GCodeBuffer/StringParser.h b/src/GCodes/GCodeBuffer/StringParser.h
index 958cf6c5..28045528 100644
--- a/src/GCodes/GCodeBuffer/StringParser.h
+++ b/src/GCodes/GCodeBuffer/StringParser.h
@@ -27,7 +27,7 @@ public:
 	StringParser(GCodeBuffer& gcodeBuffer) noexcept;
 	void Init() noexcept; 													// Set it up to parse another G-code
 	void Diagnostics(MessageType mtype) noexcept;							// Write some debug info
-	bool Put(char c) noexcept __attribute__((hot));							// Add a character to the end
+	bool Put(char c) noexcept SPEED_CRITICAL;				// Add a character to the end
 	void PutCommand(const char *str) noexcept;								// Put a complete command but don't decode it
 	void DecodeCommand() noexcept;											// Decode the next command in the line
 	void PutAndDecode(const char *str, size_t len) noexcept;				// Add an entire string, overwriting any existing content
@@ -44,10 +44,10 @@ public:
 	bool IsLastCommand() const noexcept;
 	bool ContainsExpression() const noexcept { return seenExpression; }
 
-	bool Seen(char c) noexcept __attribute__((hot));							// Is a character present?
-	float GetFValue() THROWS(GCodeException) __attribute__((hot));				// Get a float after a key letter
-	float GetDistance() THROWS(GCodeException);									// Get a distance or coordinate and convert it from inches to mm if necessary
-	int32_t GetIValue() THROWS(GCodeException) __attribute__((hot));			// Get an integer after a key letter
+	bool Seen(char c) noexcept SPEED_CRITICAL;					// Is a character present?
+	float GetFValue() THROWS(GCodeException) SPEED_CRITICAL;	// Get a float after a key letter
+	float GetDistance() THROWS(GCodeException) SPEED_CRITICAL;	// Get a distance or coordinate and convert it from inches to mm if necessary
+	int32_t GetIValue() THROWS(GCodeException) SPEED_CRITICAL;	// Get an integer after a key letter
 	uint32_t GetUIValue() THROWS(GCodeException);								// Get an unsigned integer value
 	DriverId GetDriverId() THROWS(GCodeException);								// Get a driver ID
 	void GetIPAddress(IPAddress& returnedIp) THROWS(GCodeException);			// Get an IP address quad after a key letter
@@ -57,7 +57,7 @@ public:
 	void GetQuotedString(const StringRef& str, bool allowEmpty = false) THROWS(GCodeException);	// Get and copy a quoted string
 	void GetPossiblyQuotedString(const StringRef& str, bool allowEmpty = false) THROWS(GCodeException);	// Get and copy a string which may or may not be quoted
 	void GetReducedString(const StringRef& str) THROWS(GCodeException);			// Get and copy a quoted string, removing certain characters
-	void GetFloatArray(float arr[], size_t& length, bool doPad) THROWS(GCodeException) __attribute__((hot)); // Get a colon-separated list of floats after a key letter
+	void GetFloatArray(float arr[], size_t& length, bool doPad) THROWS(GCodeException) SPEED_CRITICAL; // Get a colon-separated list of floats after a key letter
 	void GetIntArray(int32_t arr[], size_t& length, bool doPad) THROWS(GCodeException);		// Get a :-separated list of ints after a key letter
 	void GetUnsignedArray(uint32_t arr[], size_t& length, bool doPad) THROWS(GCodeException);	// Get a :-separated list of unsigned ints after a key letter
 	void GetDriverIdArray(DriverId arr[], size_t& length) THROWS(GCodeException);	// Get a :-separated list of drivers after a key letter
diff --git a/src/GCodes/GCodes.h b/src/GCodes/GCodes.h
index 38683584..b459876b 100644
--- a/src/GCodes/GCodes.h
+++ b/src/GCodes/GCodes.h
@@ -332,7 +332,7 @@ private:
 	void HandleReply(GCodeBuffer& gb, OutputBuffer *reply) noexcept;
 	void HandleReplyPreserveResult(GCodeBuffer& gb, GCodeResult rslt, const char *reply) noexcept;	// Handle G-Code replies
 
-	bool DoStraightMove(GCodeBuffer& gb, bool isCoordinated, const char *& err) __attribute__((hot));	// Execute a straight move
+	bool DoStraightMove(GCodeBuffer& gb, bool isCoordinated, const char *& err) SPEED_CRITICAL;	// Execute a straight move
 	bool DoArcMove(GCodeBuffer& gb, bool clockwise, const char *& err)				// Execute an arc move
 		pre(segmentsLeft == 0; resourceOwners[MoveResource] == &gb);
 	void FinaliseMove(GCodeBuffer& gb) noexcept;									// Adjust the move parameters to account for segmentation and/or part of the move having been done already
diff --git a/src/Movement/DDA.cpp b/src/Movement/DDA.cpp
index f26f08ce..5c61a1ef 100644
--- a/src/Movement/DDA.cpp
+++ b/src/Movement/DDA.cpp
@@ -1789,9 +1789,6 @@ void DDA::CheckEndstops(Platform& platform) noexcept
 #endif
 }
 
-// The remaining functions are speed-critical, so use full optimisation
-// The GCC optimize pragma appears to be broken, if we try to force O3 optimisation here then functions are never inlined
-
 // Start executing this move. Must be called with interrupts disabled or basepri >= set interrupt priority, to avoid a race condition.
 void DDA::Start(Platform& p, uint32_t tim) noexcept
 pre(state == frozen)
diff --git a/src/Movement/DDA.h b/src/Movement/DDA.h
index c178d0a9..1098be67 100644
--- a/src/Movement/DDA.h
+++ b/src/Movement/DDA.h
@@ -39,21 +39,21 @@ public:
 
 	DDA(DDA* n) noexcept;
 
-	bool InitStandardMove(DDARing& ring, const RawMove &nextMove, bool doMotorMapping) noexcept __attribute__ ((hot));	// Set up a new move, returning true if it represents real movement
+	bool InitStandardMove(DDARing& ring, const RawMove &nextMove, bool doMotorMapping) noexcept  SPEED_CRITICAL;	// Set up a new move, returning true if it represents real movement
 	bool InitLeadscrewMove(DDARing& ring, float feedrate, const float amounts[MaxDriversPerAxis]) noexcept;		// Set up a leadscrew motor move
 #if SUPPORT_ASYNC_MOVES
 	bool InitAsyncMove(DDARing& ring, const AsyncMove& nextMove) noexcept;			// Set up an async move
 #endif
 
-	void Start(Platform& p, uint32_t tim) noexcept __attribute__ ((hot));			// Start executing the DDA, i.e. move the move.
-	void StepDrivers(Platform& p) noexcept __attribute__ ((hot));					// Take one step of the DDA, called by timed interrupt.
-	bool ScheduleNextStepInterrupt(StepTimer& timer) const noexcept;				// Schedule the next interrupt, returning true if we can't because it is already due
+	void Start(Platform& p, uint32_t tim) noexcept SPEED_CRITICAL;	// Start executing the DDA, i.e. move the move.
+	void StepDrivers(Platform& p) noexcept SPEED_CRITICAL;			// Take one step of the DDA, called by timed interrupt.
+	bool ScheduleNextStepInterrupt(StepTimer& timer) const noexcept SPEED_CRITICAL;	// Schedule the next interrupt, returning true if we can't because it is already due
 
 	void SetNext(DDA *n) noexcept { next = n; }
 	void SetPrevious(DDA *p) noexcept { prev = p; }
 	void Complete() noexcept { state = completed; }
 	bool Free() noexcept;
-	void Prepare(uint8_t simMode, float extrusionPending[]) noexcept __attribute__ ((hot));	// Calculate all the values and freeze this DDA
+	void Prepare(uint8_t simMode, float extrusionPending[]) noexcept SPEED_CRITICAL;	// Calculate all the values and freeze this DDA
 	bool HasStepError() const noexcept;
 	bool CanPauseAfter() const noexcept;
 	bool IsPrintingMove() const noexcept { return flags.isPrintingMove; }			// Return true if this involves both XY movement and extrusion
@@ -170,11 +170,11 @@ public:
 private:
 	DriveMovement *FindDM(size_t drive) const noexcept;						// find the DM for a drive if there is one even if it is completed
 	DriveMovement *FindActiveDM(size_t drive) const noexcept;				// find the DM for a drive if there is one but only if it is active
-	void RecalculateMove(DDARing& ring) noexcept __attribute__ ((hot));
-	void MatchSpeeds() noexcept __attribute__ ((hot));
+	void RecalculateMove(DDARing& ring) noexcept SPEED_CRITICAL;
+	void MatchSpeeds() noexcept SPEED_CRITICAL;
 	void ReduceHomingSpeed() noexcept;										// called to reduce homing speed when a near-endstop is triggered
 	void StopDrive(size_t drive) noexcept;									// stop movement of a drive and recalculate the endpoint
-	void InsertDM(DriveMovement *dm) noexcept __attribute__ ((hot));
+	void InsertDM(DriveMovement *dm) noexcept SPEED_CRITICAL;
 	void DeactivateDM(size_t drive) noexcept;
 	void ReleaseDMs() noexcept;
 	bool IsDecelerationMove() const noexcept;								// return true if this move is or have been might have been intended to be a deceleration-only move
@@ -186,7 +186,7 @@ private:
 	int32_t PrepareRemoteExtruder(size_t drive, float& extrusionPending, float speedChange) const noexcept;
 #endif
 
-	static void DoLookahead(DDARing& ring, DDA *laDDA) noexcept __attribute__ ((hot));	// Try to smooth out moves in the queue
+	static void DoLookahead(DDARing& ring, DDA *laDDA) noexcept  SPEED_CRITICAL;	// Try to smooth out moves in the queue
     static float Normalise(float v[], AxesBitmap unitLengthAxes) noexcept;  // Normalise a vector to unit length over the specified axes
     static float Normalise(float v[]) noexcept; 							// Normalise a vector to unit length over all axes
 	float NormaliseLinearMotion(AxesBitmap linearAxes) noexcept;			// Make the direction vector unit-normal in XYZ
diff --git a/src/Movement/DDARing.h b/src/Movement/DDARing.h
index 44bc9ad2..35cf3f15 100644
--- a/src/Movement/DDARing.h
+++ b/src/Movement/DDARing.h
@@ -23,21 +23,21 @@ public:
 
 	void RecycleDDAs() noexcept;
 	bool CanAddMove() const noexcept;
-	bool AddStandardMove(const RawMove &nextMove, bool doMotorMapping) noexcept __attribute__ ((hot));	// Set up a new move, returning true if it represents real movement
+	bool AddStandardMove(const RawMove &nextMove, bool doMotorMapping) noexcept SPEED_CRITICAL;	// Set up a new move, returning true if it represents real movement
 	bool AddSpecialMove(float feedRate, const float coords[MaxDriversPerAxis]) noexcept;
 #if SUPPORT_ASYNC_MOVES
 	bool AddAsyncMove(const AsyncMove& nextMove) noexcept;
 #endif
 
-	void Spin(uint8_t simulationMode, bool shouldStartMove) noexcept;					// Try to process moves in the ring
+	void Spin(uint8_t simulationMode, bool shouldStartMove) noexcept SPEED_CRITICAL;	// Try to process moves in the ring
 	bool IsIdle() const noexcept;														// Return true if this DDA ring is idle
 
 	float PushBabyStepping(size_t axis, float amount) noexcept;							// Try to push some babystepping through the lookahead queue, returning the amount pushed
 
-	void Interrupt(Platform& p) noexcept;												// Check endstops, generate step pulses
+	void Interrupt(Platform& p) noexcept SPEED_CRITICAL;				// Check endstops, generate step pulses
 	void OnMoveCompleted(DDA *cdda, Platform& p) noexcept;								// called when the state has been set to 'completed'
-	bool ScheduleNextStepInterrupt() noexcept;											// Schedule the next step interrupt, returning true if we failed because it is due immediately
-	void CurrentMoveCompleted() noexcept __attribute__ ((hot));							// Signal that the current move has just been completed
+	bool ScheduleNextStepInterrupt() noexcept SPEED_CRITICAL;			// Schedule the next step interrupt, returning true if we failed because it is due immediately
+	void CurrentMoveCompleted() noexcept SPEED_CRITICAL;				// Signal that the current move has just been completed
 
 	uint32_t ExtruderPrintingSince() const noexcept { return extrudersPrintingSince; }	// When we started doing normal moves after the most recent extruder-only move
 	int32_t GetAccumulatedExtrusion(size_t extruder, size_t drive, bool& isPrinting) noexcept;
@@ -84,7 +84,7 @@ public:
 	bool SetWaitingToEmpty() noexcept;
 
 private:
-	bool StartNextMove(Platform& p, uint32_t startTime) noexcept __attribute__ ((hot));	// Start the next move, returning true if laser or IObits need to be controlled
+	bool StartNextMove(Platform& p, uint32_t startTime) noexcept SPEED_CRITICAL;	// Start the next move, returning true if laser or IObits need to be controlled
 	void PrepareMoves(DDA *firstUnpreparedMove, int32_t moveTimeLeft, unsigned int alreadyPrepared, uint8_t simulationMode) noexcept;
 
 	static void TimerCallback(CallbackParameter p) noexcept;
diff --git a/src/Movement/DriveMovement.h b/src/Movement/DriveMovement.h
index 242f8a52..3fa3b336 100644
--- a/src/Movement/DriveMovement.h
+++ b/src/Movement/DriveMovement.h
@@ -134,11 +134,11 @@ public:
 
 	DriveMovement(DriveMovement *next) noexcept;
 
-	bool CalcNextStepTimeCartesian(const DDA &dda, bool live) noexcept __attribute__ ((hot));
-	bool CalcNextStepTimeDelta(const DDA &dda, bool live) noexcept __attribute__ ((hot));
-	bool PrepareCartesianAxis(const DDA& dda, const PrepParams& params) noexcept __attribute__ ((hot));
-	bool PrepareDeltaAxis(const DDA& dda, const PrepParams& params) noexcept __attribute__ ((hot));
-	bool PrepareExtruder(const DDA& dda, const PrepParams& params, float& extrusionPending, float speedChange, bool doCompensation) noexcept __attribute__ ((hot));
+	bool CalcNextStepTimeCartesian(const DDA &dda, bool live) noexcept SPEED_CRITICAL;
+	bool CalcNextStepTimeDelta(const DDA &dda, bool live) noexcept SPEED_CRITICAL;
+	bool PrepareCartesianAxis(const DDA& dda, const PrepParams& params) noexcept SPEED_CRITICAL;
+	bool PrepareDeltaAxis(const DDA& dda, const PrepParams& params) noexcept SPEED_CRITICAL;
+	bool PrepareExtruder(const DDA& dda, const PrepParams& params, float& extrusionPending, float speedChange, bool doCompensation) noexcept SPEED_CRITICAL;
 	void ReduceSpeed(uint32_t inverseSpeedFactor) noexcept;
 	void DebugPrint() const noexcept;
 	int32_t GetNetStepsLeft() const noexcept;
@@ -160,8 +160,8 @@ public:
 	static void Release(DriveMovement *item) noexcept;
 
 private:
-	bool CalcNextStepTimeCartesianFull(const DDA &dda, bool live) noexcept __attribute__ ((hot));
-	bool CalcNextStepTimeDeltaFull(const DDA &dda, bool live) noexcept __attribute__ ((hot));
+	bool CalcNextStepTimeCartesianFull(const DDA &dda, bool live) noexcept SPEED_CRITICAL;
+	bool CalcNextStepTimeDeltaFull(const DDA &dda, bool live) noexcept SPEED_CRITICAL;
 
 	static DriveMovement *freeList;
 	static int numFree;
diff --git a/src/Movement/Move.h b/src/Movement/Move.h
index 11f9efcc..70a3e167 100644
--- a/src/Movement/Move.h
+++ b/src/Movement/Move.h
@@ -64,7 +64,7 @@ public:
 	int32_t GetEndPoint(size_t drive) const noexcept;					 	// Get the current position of a motor
 	float LiveCoordinate(unsigned int axisOrExtruder, const Tool *tool) noexcept; // Gives the last point at the end of the last complete DDA
 	bool WaitingForAllMovesFinished() noexcept;								// Tell the lookahead ring we are waiting for it to empty and return true if it is
-	void DoLookAhead() noexcept __attribute__ ((hot));						// Run the look-ahead procedure
+	void DoLookAhead() noexcept SPEED_CRITICAL;			// Run the look-ahead procedure
 	void SetNewPosition(const float positionNow[MaxAxesPlusExtruders], bool doBedCompensation) noexcept; // Set the current position to be this
 	void SetLiveCoordinates(const float coords[MaxAxesPlusExtruders]) noexcept;	// Force the live coordinates (see above) to be these
 	void ResetExtruderPositions() noexcept;									// Resets the extrusion amounts of the live coordinates
diff --git a/src/Movement/StepTimer.cpp b/src/Movement/StepTimer.cpp
index 8f4a8b77..f77e68be 100644
--- a/src/Movement/StepTimer.cpp
+++ b/src/Movement/StepTimer.cpp
@@ -217,7 +217,7 @@ void StepTimer::DisableTimerInterrupt() noexcept
 }
 
 // Step pulse timer interrupt
-extern "C" void STEP_TC_HANDLER() noexcept __attribute__ ((hot));
+extern "C" void STEP_TC_HANDLER() noexcept SPEED_CRITICAL;
 
 void STEP_TC_HANDLER() noexcept
 {
diff --git a/src/Movement/StepTimer.h b/src/Movement/StepTimer.h
index d72adcbc..5b0a7849 100644
--- a/src/Movement/StepTimer.h
+++ b/src/Movement/StepTimer.h
@@ -27,19 +27,19 @@ public:
 	void SetCallback(TimerCallbackFunction cb, CallbackParameter param) noexcept;
 
 	// Schedule a callback at a particular tick count, returning true if it was not scheduled because it is already due or imminent
-	bool ScheduleCallback(Ticks when) noexcept;
+	bool ScheduleCallback(Ticks when) noexcept SPEED_CRITICAL;
 
 	// As ScheduleCallback but base priority >= NvicPriorityStep when called. Can be called from within a callback.
-	bool ScheduleCallbackFromIsr(Ticks when) noexcept;
+	bool ScheduleCallbackFromIsr(Ticks when) noexcept SPEED_CRITICAL;
 
 	// Check whether a callback really is due, schedule it if not. Returns true if it really is due. Can be called from within a callback.
-	bool ScheduleCallbackFromIsr() noexcept;
+	bool ScheduleCallbackFromIsr() noexcept SPEED_CRITICAL;
 
 	// Cancel any scheduled callbacks
 	void CancelCallback() noexcept;
 
 	// As CancelCallback but base priority >= NvicPriorityStep when called
-	void CancelCallbackFromIsr() noexcept;
+	void CancelCallbackFromIsr() noexcept SPEED_CRITICAL;
 
 	// Initialise the timer system
 	static void Init() noexcept;
@@ -48,7 +48,7 @@ public:
 	static void DisableTimerInterrupt() noexcept;
 
 	// Get the current tick count
-	static Ticks GetTimerTicks() noexcept __attribute__ ((hot));
+	static Ticks GetTimerTicks() noexcept SPEED_CRITICAL;
 
 	// Get the current tick count when we only need a 16-bit value. Faster than GetTimerTicks() on the SAM4S and SAME70.
 	static uint16_t GetTimerTicks16() noexcept;
diff --git a/src/Movement/StepperDrivers/TMC22xx.cpp b/src/Movement/StepperDrivers/TMC22xx.cpp
index e39879e1..957dcbe8 100644
--- a/src/Movement/StepperDrivers/TMC22xx.cpp
+++ b/src/Movement/StepperDrivers/TMC22xx.cpp
@@ -469,8 +469,8 @@ public:
 
 	bool DriverAssumedPresent() const noexcept { return numWrites != 0 || numTimeouts < DriverNotPresentTimeouts; }
 
-	void TransferDone() noexcept __attribute__ ((hot));		// called by the ISR when the SPI transfer has completed
-	void StartTransfer() noexcept __attribute__ ((hot));	// called to start a transfer
+	void TransferDone() noexcept SPEED_CRITICAL;	// called by the ISR when the SPI transfer has completed
+	void StartTransfer() noexcept SPEED_CRITICAL;	// called to start a transfer
 	void TransferTimedOut() noexcept
 	{
 		if (DriverAssumedPresent())
@@ -526,11 +526,11 @@ private:
 	void SetUartMux() noexcept;
 #endif
 #if (TMC22xx_HAS_MUX || TMC22xx_SINGLE_DRIVER) && !TMC22xx_USE_SLAVEADDR
-	static void SetupDMASend(uint8_t regnum, uint32_t outVal) noexcept __attribute__ ((hot));	// set up the DMAC to send a register
-	static void SetupDMARead(uint8_t regnum, uint8_t crc) noexcept __attribute__ ((hot));		// set up the DMAC to receive a register
+	static void SetupDMASend(uint8_t regnum, uint32_t outVal) noexcept SPEED_CRITICAL;	// set up the DMAC to send a register
+	static void SetupDMARead(uint8_t regnum, uint8_t crc) noexcept SPEED_CRITICAL;		// set up the DMAC to receive a register
 #else
-	void SetupDMASend(uint8_t regnum, uint32_t outVal) noexcept __attribute__ ((hot));			// set up the DMAC to send a register
-	void SetupDMARead(uint8_t regnum) noexcept __attribute__ ((hot));							// set up the DMAC to receive a register
+	void SetupDMASend(uint8_t regnum, uint32_t outVal) noexcept SPEED_CRITICAL;		// set up the DMAC to send a register
+	void SetupDMARead(uint8_t regnum) noexcept SPEED_CRITICAL;							// set up the DMAC to receive a register
 #endif
 
 #if HAS_STALL_DETECT
@@ -1555,7 +1555,7 @@ void TransferCompleteCallback(CallbackParameter, DmaCallbackReason reason) noexc
 #  endif
 
 // ISR for the single UART
-extern "C" void TMC22xx_UART_Handler() noexcept __attribute__ ((hot));
+extern "C" void TMC22xx_UART_Handler() noexcept SPEED_CRITICAL;
 
 void TMC22xx_UART_Handler() noexcept
 {
@@ -1569,13 +1569,13 @@ void TMC22xx_UART_Handler() noexcept
 #else
 
 // ISRs for the individual UARTs
-extern "C" void UART_TMC_DRV0_Handler() noexcept __attribute__ ((hot));
+extern "C" void UART_TMC_DRV0_Handler() noexcept SPEED_CRITICAL;
 void UART_TMC_DRV0_Handler() noexcept
 {
 	driverStates[0].UartTmcHandler();
 }
 
-extern "C" void UART_TMC_DRV1_Handler() noexcept __attribute__ ((hot));
+extern "C" void UART_TMC_DRV1_Handler() noexcept SPEED_CRITICAL;
 void UART_TMC_DRV1_Handler() noexcept
 {
 	driverStates[1].UartTmcHandler();
diff --git a/src/Movement/StepperDrivers/TMC2660.cpp b/src/Movement/StepperDrivers/TMC2660.cpp
index 7c0f8034..bc672b50 100644
--- a/src/Movement/StepperDrivers/TMC2660.cpp
+++ b/src/Movement/StepperDrivers/TMC2660.cpp
@@ -226,8 +226,8 @@ public:
 	bool SetRegister(SmartDriverRegister reg, uint32_t regVal) noexcept;
 	uint32_t GetRegister(SmartDriverRegister reg) const noexcept;
 
-	void TransferDone() noexcept __attribute__ ((hot));						// called by the ISR when the SPI transfer has completed
-	void StartTransfer() noexcept __attribute__ ((hot));					// called to start a transfer
+	void TransferDone() noexcept SPEED_CRITICAL;		// called by the ISR when the SPI transfer has completed
+	void StartTransfer() noexcept SPEED_CRITICAL;		// called to start a transfer
 
 	uint32_t ReadLiveStatus() const noexcept;
 	uint32_t ReadAccumulatedStatus(uint32_t bitsToKeep) noexcept;
@@ -244,7 +244,7 @@ private:
 		maxSgLoadRegister = 0;
 	}
 
-	static void SetupDMA(uint32_t outVal) noexcept __attribute__ ((hot));	// set up the PDC to send a register and receive the status
+	static void SetupDMA(uint32_t outVal) noexcept SPEED_CRITICAL;	// set up the PDC to send a register and receive the status
 
 	static constexpr unsigned int NumRegisters = 5;			// the number of registers that we write to
 	volatile uint32_t registers[NumRegisters];				// the values we want the TMC2660 writable registers to have
@@ -849,7 +849,7 @@ inline void TmcDriverState::StartTransfer() noexcept
 # error TMC handler name not defined
 #endif
 
-extern "C" void TMC2660_SPI_Handler(void) noexcept __attribute__ ((hot));
+extern "C" void TMC2660_SPI_Handler(void) noexcept SPEED_CRITICAL;
 
 void TMC2660_SPI_Handler(void) noexcept
 {
diff --git a/src/Platform.h b/src/Platform.h
index 42cebe3a..1b0d53e1 100644
--- a/src/Platform.h
+++ b/src/Platform.h
@@ -357,7 +357,7 @@ public:
 	const MacAddress& GetDefaultMacAddress() const noexcept { return defaultMacAddress; }
 
 	// Timing
-	void Tick() noexcept __attribute__((hot));						// Process a systick interrupt
+	void Tick() noexcept SPEED_CRITICAL;			// Process a systick interrupt
 
 	// Real-time clock
 	bool IsDateTimeSet() const noexcept { return realTime != 0; }	// Has the RTC been set yet?
diff --git a/src/RepRapFirmware.h b/src/RepRapFirmware.h
index e83c98e0..c54e5fb0 100644
--- a/src/RepRapFirmware.h
+++ b/src/RepRapFirmware.h
@@ -98,6 +98,8 @@ inline void memcpyf(float *dst, const float *src, size_t numFloats) noexcept
 
 #endif
 
+#define SPEED_CRITICAL	__attribute__((optimize("O2")))
+
 // API level definition.
 // ApiLevel 1 is the first level that supports rr_model.
 constexpr unsigned int ApiLevel = 1;