Fix issue with main task stack usage too high after previous change

Author: dc42

src/Platform/RepRap.cpp

@@ -730,8 +730,7 @@ void RepRap::Spin() noexcept
 	// Check if we need to send diagnostics
 	if (diagnosticsDestination != MessageType::NoDestinationMessage)
 	{
-		String<GCodeReplyLength> buf;
-		Diagnostics(diagnosticsDestination, buf.GetRef());
+		GenerateDeferredDiagnostics(diagnosticsDestination);				// call out to separate function to keep stack usage under control
 		diagnosticsDestination = MessageType::NoDestinationMessage;
 	}
 
@@ -808,6 +807,13 @@ void RepRap::Spin() noexcept
 	RTOSIface::Yield();
 }
 
+// Send diagnostics to the specified destination. This is in a separate function so that the large string doesn't take up main task stack space all the time.
+__attribute__((noinline)) void RepRap::GenerateDeferredDiagnostics(MessageType destination) noexcept
+{
+	String<GCodeReplyLength> buf;
+	Diagnostics(destination, buf.GetRef());
+}
+
 void RepRap::Timing(const StringRef& reply) noexcept
 {
 	reply.lcatf("Slowest loop: %.2fms; fastest: %.2fms", (double)(slowLoop * StepClocksToMillis), (double)(fastLoop * StepClocksToMillis));

src/Platform/RepRap.h

@@ -178,6 +178,7 @@ class RepRap final INHERIT_OBJECT_MODEL
 	ReadWriteLock *_ecv_null GetObjectLock(unsigned int tableNumber) const noexcept override;
 
 private:
+	__attribute__((noinline)) void GenerateDeferredDiagnostics(MessageType destination) noexcept;
 
 #ifndef DUET_NG			// Duet 2 doesn't currently need this feature, so omit it to save memory
 	struct DebugLogRecord