Add synchronization mechanism for entering sleep mode.

When the APT status is APP_PREPARE_SLEEPMODE, the application main thread should call aptSignalReadyForSleep() to signal that it is ready to enter sleep mode, and then call aptWaitStatusEvent() as usual.

Example code:

APP_STATUS status;
while ((status = aptGetStatus()) != APP_EXITING)
{
	if(status==APP_RUNNING)
	{
		// application logic here
	}
	else if(status == APP_SUSPENDING)
	{
		aptReturnToMenu();
	}
	else if(status == APP_PREPARE_SLEEPMODE)
	{
		aptSignalReadyForSleep();
		aptWaitStatusEvent();
	}
}

This maybe isn't the proper/recommended way to do sleep mode, but I tested it multiple times and it always worked reliably.

(note: maybe the sample code above will not work if GPU drawing is done in a separate thread, haven't tested that)

libctru/include/3ds/services/apt.h

@@ -48,6 +48,7 @@ u32 aptGetStatusPower();//This can be used when the status is APP_SUSPEND* to ch
 void aptSetStatusPower(u32 status);
 void aptReturnToMenu();//This should be called by the user application when aptGetStatus() returns APP_SUSPENDING, not calling this will result in return-to-menu being disabled with the status left at APP_SUSPENDING. This function will not return until the system returns to the application, or when the status was changed to APP_EXITING.
 void aptWaitStatusEvent();
+void aptSignalReadyForSleep();
 NS_APPID aptGetMenuAppID();
 
 Result APT_GetLockHandle(Handle* handle, u16 flags, Handle* lockHandle);

libctru/source/services/apt.c

@@ -26,6 +26,7 @@ Handle aptStatusEvent = 0;
 APP_STATUS aptStatus = APP_NOTINITIALIZED;
 APP_STATUS aptStatusBeforeSleep = APP_NOTINITIALIZED;
 u32 aptStatusPower = 0;
+Handle aptSleepSync = 0;
 
 u32 aptParameters[0x1000/4]; //TEMP
 
@@ -204,21 +205,24 @@ static void __handle_notification() {
 	case APTSIGNAL_PREPARESLEEP:
 		// Reply to sleep-request.
 		aptStatusBeforeSleep = aptGetStatus();
+		aptSetStatus(APP_PREPARE_SLEEPMODE);
+		svcWaitSynchronization(aptSleepSync, U64_MAX);
+		svcClearEvent(aptSleepSync);
+		
 		aptOpenSession();
 		APT_ReplySleepQuery(NULL, currentAppId, 0x1);
 		aptCloseSession();
-
-		aptSetStatus(APP_PREPARE_SLEEPMODE);
 		break;
 
 	case APTSIGNAL_ENTERSLEEP:
 		if(aptGetStatus() == APP_PREPARE_SLEEPMODE)
 		{
 			// Report into sleep-mode.
+			aptSetStatus(APP_SLEEPMODE);
+			
 			aptOpenSession();
 			APT_ReplySleepNotificationComplete(NULL, currentAppId);
 			aptCloseSession();
-			aptSetStatus(APP_SLEEPMODE);
 		}
 		break;
 
@@ -319,6 +323,7 @@ Result aptInit(void)
 	}
 
 	svcCreateEvent(&aptStatusEvent, 0);
+	svcCreateEvent(&aptSleepSync, 0);
 	return 0;
 }
 
@@ -345,6 +350,8 @@ void aptExit()
 		aptCloseSession();
 	}
 	
+	svcCloseHandle(aptSleepSync);
+
 	svcCloseHandle(aptStatusMutex);
 	//svcCloseHandle(aptLockHandle);
 	svcCloseHandle(aptStatusEvent);
@@ -421,7 +428,7 @@ void aptSetStatus(APP_STATUS status)
 
 	svcWaitSynchronization(aptStatusMutex, U64_MAX);
 
-	prevstatus = status;
+	prevstatus = aptStatus;
 	aptStatus = status;
 
 	if(prevstatus != APP_NOTINITIALIZED)
@@ -461,6 +468,11 @@ void aptCloseSession()
 	svcReleaseMutex(aptLockHandle);
 }
 
+void aptSignalReadyForSleep()
+{
+	svcSignalEvent(aptSleepSync);
+}
+
 Result APT_GetLockHandle(Handle* handle, u16 flags, Handle* lockHandle)
 {
 	if(!handle)handle=&aptuHandle;