--- /n/downloads/devusb.c	Tue Feb 14 20:42:27 2023
+++ /sys/src/9/bcm/devusb.c	Tue Feb 14 11:31:28 2023
@@ -88,6 +88,7 @@
 	CMdebugep,		/* debug n (set/clear debug for this ep) */
 	CMname,			/* name str (show up as #u/name as well) */
 	CMtmout,		/* timeout n (activate timeouts for ep) */
+	CMsampledelay,		/* maximum delay introduced by buffering (iso) */
 	CMpreset,		/* reset the port */
 
 	/* Hub feature selectors */
@@ -128,6 +129,7 @@
 	{CMclrhalt,	"clrhalt",	1},
 	{CMname,	"name",		2},
 	{CMtmout,	"timeout",	2},
+	{CMsampledelay,	"sampledelay",	2},
 	{CMpreset,	"reset",	1},
 };
 
@@ -1387,6 +1389,11 @@
 		ep->tmout = strtoul(cb->f[1], nil, 0);
 		if(ep->tmout != 0 && ep->tmout < Xfertmout)
 			ep->tmout = Xfertmout;
+		break;
+	case CMsampledelay:
+		if(ep->ttype != Tiso)
+			error("ctl ignored for this endpoint type");
+		ep->sampledelay = strtoul(cb->f[1], nil, 0);
 		break;
 	case CMpreset:
 		deprint("usb epctl %s\n", cb->f[0]);
--- /n/downloads/usbxhci.c	Tue Feb 14 20:41:33 2023
+++ /sys/src/9/bcm/usbxhci.c	Tue Feb 14 11:24:53 2023
@@ -194,6 +194,7 @@
 
 	int	stopped;
 
+	int	*residue;
 	Wait	*pending;
 	Lock;
 };
@@ -277,6 +278,10 @@
 	u32int	incr;
 	u32int	tdsz;
 
+	/* isoread */
+	u32int	rp0;
+	u32int	frame0;
+
 	int	nleft;
 };
 
@@ -1100,10 +1105,17 @@
 {
 	if(io->ring == nil)
 		return;
-	io->frame = 0;
-	io->period = ep->pollival<<3*(ep->dev->speed == Fullspeed);
-	io->incr = (ep->hz*io->period<<8)/8000;
-	io->tdsz = (io->incr+255>>8)*ep->samplesz;
+	io->rp0 = io->ring->wp;
+	io->frame0 = io->frame = 0;
+	io->period = ep->pollival << 3*(ep->dev->speed == Fullspeed || ep->dev->speed == Lowspeed);
+	if(io->ring->id & 1){
+		io->ring->residue = smalloc((io->ring->mask+1)*sizeof(io->ring->residue[0]));
+		io->incr = 0;
+		io->tdsz = ep->maxpkt*ep->ntds;
+	} else {
+		io->incr = ((vlong)ep->hz*ep->pollival<<8)/1000;
+		io->tdsz = (io->incr+255>>8)*ep->samplesz;
+	}
 	io->b = allocb((io->ring->mask+1)*io->tdsz);
 }
 
@@ -1336,10 +1348,10 @@
 	}
 	µ = io->period;
 	ctlr = ep->hp->aux;
-	if(needrecover(ctlr))
-		error(Erecover);
 	for(i = io->frame;; i++){
 		for(;;){
+			if(needrecover(ctlr))
+				error(Erecover);
 			m = (int)(io->ring->wp - io->ring->rp);
 			if(m <= 0)
 				i = (80 + µframe(ctlr))/µ;
@@ -1367,11 +1379,13 @@
 	io->frame = i;
 	while(io->ring->rp != io->ring->wp){
 		int d = (int)(i*µ - µframe(ctlr))/8;
-		//d -= ep->sampledelay*1000 / ep->hz;
+		d -= ep->sampledelay*1000 / ep->hz;
 		if(d < 5)
 			break;
 		*io->ring->doorbell = io->ring->id;
 		tsleep(&up->sleep, return0, nil, d);
+			if(needrecover(ctlr))
+				error(Erecover);
 	}
 	qunlock(io);
 	poperror();
--- /n/downloads/audio.h	Tue Feb 14 23:52:55 2023
+++ /sys/src/cmd/usb/audio/audio.h	Tue Feb 14 23:29:03 2023
@@ -39,6 +39,11 @@
 
 #define SAMPLING_FREQ_CONTROL 0x01
 
+#define DSPEEDPLAY 44100
+#define DSPEEDREC 44100
+/* 40ms */
+#define DDELAY 1764
+
 typedef struct Audioalt Audioalt;
 
 struct Audioalt {
--- /n/downloads/audio.c	Tue Feb 14 23:52:36 2023
+++ /sys/src/cmd/usb/audio/audio.c	Wed Feb 15 01:00:51 2023
@@ -25,7 +25,7 @@
 
 int verbose;
 int setrec = 0;
-int defaultspeed[2] = {44100, 44100};
+int defaultspeed[2]= { DSPEEDPLAY, DSPEEDREC};
 Dev *buttondev;
 Dev *epdev[2];
 
@@ -372,6 +372,8 @@
 	value[0] = defaultspeed[Record];
 	if(endpt[Record] >= 0 && setcontrol(Record, "speed", value) < 0)
 		fprint(2, "%s: can't set record speed\n", argv0);
+	value[0] = DDELAY;
+	setcontrol(Play, "delay", value);
 	value[0] = 0;
 	setcontrol(Play, "mute", value);
 
--- /n/downloads/audioctl.c	Tue Feb 14 20:43:26 2023
+++ /sys/src/cmd/usb/audio/audioctl.c	Wed Feb 15 01:13:48 2023
@@ -18,7 +18,7 @@
 
 Audiocontrol controls[2][Ncontrol] = {
 	{
-	[Speed_control] = {		"speed",	0, {0}, 0,	44100,	Undef},
+	[Speed_control] = {		"speed",	0, {0}, 0,	DSPEEDPLAY,	Undef},
 	[Mute_control] = {		"mute",		0, {0}, 0,	0,	Undef},
 	[Volume_control] = {		"volume",	0, {0}, 0,	0,	Undef},
 	[Bass_control] = {		"bass",		0, {0}, 0,	0,	Undef},
@@ -26,14 +26,14 @@
 	[Treble_control] = {		"treble",	0, {0}, 0,	0,	Undef},
 	[Equalizer_control] = {		"equalizer",	0, {0}, 0,	0,	Undef},
 	[Agc_control] = {		"agc",		0, {0}, 0,	0,	Undef},
-	[Delay_control] = {		"delay",	0, {0}, 0,	0,	Undef},
+	[Delay_control] = {		"delay",	1, {1}, 0,	DDELAY,	Undef},
 	[Bassboost_control] = {		"bassboost",	0, {0}, 0,	0,	Undef},
 	[Loudness_control] = {		"loudness",	0, {0}, 0,	0,	Undef},
 	[Channel_control] = {		"channels",	0, {0}, 0,	2,	Undef},
 	[Resolution_control] = {	"resolution",	0, {0}, 0,	16,	Undef},
 //	[Selector_control] = {		"selector",	0, {0}, 0,	0,	Undef},
 	}, {
-	[Speed_control] = {		"speed",	0, {0}, 0,	44100,	Undef},
+	[Speed_control] = {		"speed",	0, {0}, 0,	DSPEEDREC,	Undef},
 	[Mute_control] = {		"mute",		0, {0}, 0,	0,	Undef},
 	[Volume_control] = {		"volume",	0, {0}, 0,	0,	Undef},
 	[Bass_control] = {		"bass",		0, {0}, 0,	0,	Undef},
@@ -129,6 +129,15 @@
 }
 
 int
+setdelay(int rec, int delay)
+{
+	if(rec == Record && !setrec)
+		return Undef;
+	devctl(epdev[rec], "sampledelay %ld", delay);
+	return delay;
+}
+
+int
 setspeed(int rec, int speed)
 {
 	int ps, n, no, dist, i;
@@ -226,10 +235,11 @@
 	}
 	dprint(2, "Configuring %s endpoint for %d Hz\n",
 				rec?"record":"playback", speed);
-	epdev[rec] = openep(ad, endpt[rec]);
-	if(epdev[rec] == nil)
-		sysfatal("openep rec %d: %r", rec);
-
+	if(epdev[rec] == nil){
+		epdev[rec] = openep(ad, endpt[rec]);
+		if(epdev[rec] == nil)
+			sysfatal("openep rec %d: %r", rec);
+	}
 	devctl(epdev[rec], "pollival %d", da->interval);
 	devctl(epdev[rec], "samplesz %ld", controls[rec][Channel_control].value[0] *
 				controls[rec][Resolution_control].value[0]/8);
@@ -391,8 +401,11 @@
 		c->value[0] = value[0];
 		controls[rec][Speed_control].value[0] = defaultspeed[rec];
 		return 0;
-	case Volume_control:
 	case Delay_control:
+		setdelay(rec, value[0]);
+		c->value[0] = value[0];
+		return 0;
+	case Volume_control:
 		count = 2;
 		/* fall through */
 	case Mute_control:
@@ -480,8 +493,12 @@
 		if(req == Rgetcur)
 			value[0] = controls[rec][ctl].value[0];
 		return 0;
-	case Volume_control:
 	case Delay_control:
+		if(req != Rgetcur)
+			return Undef;
+		value[0] = controls[rec][ctl].value[0];
+		return 0;
+	case Volume_control:
 		count = 2;
 		/* fall through */
 	case Bass_control: