20160207timetorunwip.diff

diff --git a/src/emu/machine.cpp b/src/emu/machine.cpp
index 7c59ef6..7d0b1d2 100644
--- a/src/emu/machine.cpp
+++ b/src/emu/machine.cpp
@@ -1347,10 +1347,36 @@ void js_main_loop()
 {
 	device_scheduler * scheduler;
 	scheduler = &(jsmess_machine->scheduler());
-	attotime stoptime(scheduler->time() + attotime(0,HZ_TO_ATTOSECONDS(60)));
+	
+	// we use a requestAnimationFrame callback which is commonly 60Hz but can vary due to monitor refresh rate, low battery mode, etc.
+	// so we must empirically determine how long to run the emulation for
+	static double prev_time = 0;
+	double curr_time = emscripten_get_now();  // in ms
+	double elapsed_time = curr_time - prev_time;
+	attoseconds_t time_to_run;
+	// if we get way behind, don't do more than 1/30 of a second worth
+	if (elapsed_time < 1000.0/30.0) {
+		time_to_run = ATTOSECONDS_IN_MSEC(elapsed_time);
+	}
+	else {
+		time_to_run = HZ_TO_ATTOSECONDS(30);
+	}
+	prev_time = curr_time;
+	
+	attotime stoptime(scheduler->time() + attotime(0,time_to_run));
+	
 	while (scheduler->time() < stoptime) {
 		scheduler->timeslice();
 	}
+
+	// check the audio buffer, if we are about to run out then run a little extra
+	// (will return -1 if web audio is unavailable)
+	if (EM_ASM_INT_V({return jsmame_sample_count()}) > -1) {
+		int sample_rate = jsmess_machine->sound().first_stream()->sample_rate();
+		while (EM_ASM_INT_V({return jsmame_sample_count()}) < sample_rate/60) {
+			scheduler->timeslice();
+		}
+	}
 }
 
 void js_set_main_loop(running_machine * machine) {
diff --git a/src/osd/modules/sound/js_sound.js b/src/osd/modules/sound/js_sound.js
index b06cbb4..9075601 100644
--- a/src/osd/modules/sound/js_sound.js
+++ b/src/osd/modules/sound/js_sound.js
@@ -185,18 +185,18 @@ function get_context() {
 };
 
 function sample_count() {
-		//TODO get someone to call this from the emulator,
-		//so the emulator can do proper audio buffering by
-		//knowing how many samples are left:
-		if (!context) {
-			//Use impossible value as an error code:
-			return -1;
-		}
-		var count = rear - start;
-		if (start > rear) {
-			count += bufferSize;
-		}
-		return count;
+	//TODO get someone to call this from the emulator,
+	//so the emulator can do proper audio buffering by
+	//knowing how many samples are left:
+	if (!context) {
+		//Use impossible value as an error code:
+		return -1;
+	}
+	var count = rear - start;
+	if (start > rear) {
+		count += bufferSize;
+	}
+	return count;
 }
 
 return {