audio: fix delay control, increase default buffer delay to 40ms

just doing a single sleep isnt enougth, as we get woken
up for every block!

sys/src/9/pc/audioac97.c

@@ -381,7 +381,8 @@ ac97write(Audio *adev, void *vp, long n, vlong)
 		}
 		p += n;
 	}
-	sleep(&ring->r, outrate, ctlr);
+	while(outrate(ctlr) == 0)
+		sleep(&ring->r, outrate, ctlr);
 	return p - (uchar*)vp;
 }
 

sys/src/9/pc/audiohda.c

@@ -1288,7 +1288,8 @@ hdawrite(Audio *adev, void *vp, long n, vlong)
 		p += n;
 	}
 	hdakick(ctlr);
-	sleep(&ring->r, outrate, ctlr);
+	while(outrate(ctlr) == 0)
+		sleep(&ring->r, outrate, ctlr);
 	return p - (uchar*)vp;
 }
 

sys/src/9/pc/audiosb16.c

@@ -549,7 +549,8 @@ audiowrite(Audio *adev, void *vp, long n, vlong)
 		}
 		p += n;
 	}
-	sleep(&ctlr->vous, ratebuf, ctlr);
+	while(ratebuf(ctlr) == 0)
+		sleep(&ctlr->vous, ratebuf, ctlr);
 	return p - (uchar*)vp;
 }
 

sys/src/9/port/devaudio.c

@@ -146,7 +146,7 @@ audioattach(char *spec)
 	if((attached & i) == 0){
 		static char *settings[] = {
 			"speed 44100",
-			"delay 882",	/* 20 ms */
+			"delay 1764",	/* 40 ms */
 			"master 100",
 			"audio 100",
 			"head 100",

sys/src/cmd/nusb/audio/audio.c

@@ -14,7 +14,7 @@ struct Audio
 	int	maxfreq;
 };
 
-int audiodelay = 882;
+int audiodelay = 1764;	/* 40 ms */
 int audiofreq = 44100;
 int audiochan = 2;
 int audiores = 16;