xref: /freebsd/sys/dev/usb/gadget/g_audio.c (revision 2e5b60079b7d8c3ca68f1390cd90f305e651f8d3)
1 /*-
2  * Copyright (c) 2010 Hans Petter Selasky. All rights reserved.
3  *
4  * Redistribution and use in source and binary forms, with or without
5  * modification, are permitted provided that the following conditions
6  * are met:
7  * 1. Redistributions of source code must retain the above copyright
8  *    notice, this list of conditions and the following disclaimer.
9  * 2. Redistributions in binary form must reproduce the above copyright
10  *    notice, this list of conditions and the following disclaimer in the
11  *    documentation and/or other materials provided with the distribution.
12  *
13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
14  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
17  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
23  * SUCH DAMAGE.
24  */
25 
26 /*
27  * USB audio specs: http://www.usb.org/developers/devclass_docs/audio10.pdf
28  *		    http://www.usb.org/developers/devclass_docs/frmts10.pdf
29  *		    http://www.usb.org/developers/devclass_docs/termt10.pdf
30  */
31 
32 #include <sys/param.h>
33 __FBSDID("$FreeBSD$");
34 
35 #include <sys/stdint.h>
36 #include <sys/stddef.h>
37 #include <sys/queue.h>
38 #include <sys/systm.h>
39 #include <sys/kernel.h>
40 #include <sys/bus.h>
41 #include <sys/linker_set.h>
42 #include <sys/module.h>
43 #include <sys/lock.h>
44 #include <sys/mutex.h>
45 #include <sys/condvar.h>
46 #include <sys/sysctl.h>
47 #include <sys/sx.h>
48 #include <sys/unistd.h>
49 #include <sys/callout.h>
50 #include <sys/malloc.h>
51 #include <sys/priv.h>
52 
53 #include <dev/usb/usb.h>
54 #include <dev/usb/usb_cdc.h>
55 #include <dev/usb/usbdi.h>
56 #include <dev/usb/usbdi_util.h>
57 #include <dev/usb/usbhid.h>
58 #include "usb_if.h"
59 
60 #define	USB_DEBUG_VAR g_audio_debug
61 #include <dev/usb/usb_debug.h>
62 
63 #include <dev/usb/gadget/g_audio.h>
64 
65 enum {
66 	G_AUDIO_ISOC0_RD,
67 	G_AUDIO_ISOC1_RD,
68 	G_AUDIO_ISOC0_WR,
69 	G_AUDIO_ISOC1_WR,
70 	G_AUDIO_N_TRANSFER,
71 };
72 
73 struct g_audio_softc {
74 	struct mtx sc_mtx;
75 	struct usb_callout sc_callout;
76 	struct usb_callout sc_watchdog;
77 	struct usb_xfer *sc_xfer[G_AUDIO_N_TRANSFER];
78 
79 	int	sc_mode;
80 	int	sc_pattern_len;
81 	int	sc_throughput;
82 	int	sc_tx_interval;
83 	int	sc_state;
84 	int	sc_noise_rem;
85 
86 	int8_t	sc_pattern[G_AUDIO_MAX_STRLEN];
87 
88 	uint16_t sc_data_len[2][G_AUDIO_FRAMES];
89 
90 	int16_t	sc_data_buf[2][G_AUDIO_BUFSIZE / 2];
91 
92 	uint8_t	sc_volume_setting[32];
93 	uint8_t	sc_volume_limit[32];
94 	uint8_t	sc_sample_rate[32];
95 };
96 
97 static SYSCTL_NODE(_hw_usb, OID_AUTO, g_audio, CTLFLAG_RW, 0, "USB audio gadget");
98 
99 #ifdef USB_DEBUG
100 static int g_audio_debug = 0;
101 
102 SYSCTL_INT(_hw_usb_g_audio, OID_AUTO, debug, CTLFLAG_RWTUN,
103     &g_audio_debug, 0, "Debug level");
104 #endif
105 
106 static int g_audio_mode = 0;
107 
108 SYSCTL_INT(_hw_usb_g_audio, OID_AUTO, mode, CTLFLAG_RWTUN,
109     &g_audio_mode, 0, "Mode selection");
110 
111 static int g_audio_pattern_interval = 1000;
112 
113 SYSCTL_INT(_hw_usb_g_audio, OID_AUTO, pattern_interval, CTLFLAG_RWTUN,
114     &g_audio_pattern_interval, 0, "Pattern interval in milliseconds");
115 
116 static char g_audio_pattern_data[G_AUDIO_MAX_STRLEN];
117 
118 SYSCTL_STRING(_hw_usb_g_audio, OID_AUTO, pattern, CTLFLAG_RW,
119     &g_audio_pattern_data, sizeof(g_audio_pattern_data), "Data pattern");
120 
121 static int g_audio_throughput;
122 
123 SYSCTL_INT(_hw_usb_g_audio, OID_AUTO, throughput, CTLFLAG_RD,
124     &g_audio_throughput, sizeof(g_audio_throughput), "Throughput in bytes per second");
125 
126 static device_probe_t g_audio_probe;
127 static device_attach_t g_audio_attach;
128 static device_detach_t g_audio_detach;
129 static usb_handle_request_t g_audio_handle_request;
130 
131 static usb_callback_t g_audio_isoc_read_callback;
132 static usb_callback_t g_audio_isoc_write_callback;
133 
134 static devclass_t g_audio_devclass;
135 
136 static void g_audio_watchdog(void *arg);
137 static void g_audio_timeout(void *arg);
138 
139 static device_method_t g_audio_methods[] = {
140 	/* USB interface */
141 	DEVMETHOD(usb_handle_request, g_audio_handle_request),
142 
143 	/* Device interface */
144 	DEVMETHOD(device_probe, g_audio_probe),
145 	DEVMETHOD(device_attach, g_audio_attach),
146 	DEVMETHOD(device_detach, g_audio_detach),
147 
148 	DEVMETHOD_END
149 };
150 
151 static driver_t g_audio_driver = {
152 	.name = "g_audio",
153 	.methods = g_audio_methods,
154 	.size = sizeof(struct g_audio_softc),
155 };
156 
157 DRIVER_MODULE(g_audio, uhub, g_audio_driver, g_audio_devclass, 0, 0);
158 MODULE_DEPEND(g_audio, usb, 1, 1, 1);
159 
160 static const struct usb_config g_audio_config[G_AUDIO_N_TRANSFER] = {
161 
162 	[G_AUDIO_ISOC0_RD] = {
163 		.type = UE_ISOCHRONOUS,
164 		.endpoint = UE_ADDR_ANY,
165 		.direction = UE_DIR_RX,
166 		.flags = {.ext_buffer = 1,.pipe_bof = 1,.short_xfer_ok = 1,},
167 		.bufsize = G_AUDIO_BUFSIZE,
168 		.callback = &g_audio_isoc_read_callback,
169 		.frames = G_AUDIO_FRAMES,
170 		.usb_mode = USB_MODE_DEVICE,
171 		.if_index = 1,
172 	},
173 
174 	[G_AUDIO_ISOC1_RD] = {
175 		.type = UE_ISOCHRONOUS,
176 		.endpoint = UE_ADDR_ANY,
177 		.direction = UE_DIR_RX,
178 		.flags = {.ext_buffer = 1,.pipe_bof = 1,.short_xfer_ok = 1,},
179 		.bufsize = G_AUDIO_BUFSIZE,
180 		.callback = &g_audio_isoc_read_callback,
181 		.frames = G_AUDIO_FRAMES,
182 		.usb_mode = USB_MODE_DEVICE,
183 		.if_index = 1,
184 	},
185 
186 	[G_AUDIO_ISOC0_WR] = {
187 		.type = UE_ISOCHRONOUS,
188 		.endpoint = UE_ADDR_ANY,
189 		.direction = UE_DIR_TX,
190 		.flags = {.ext_buffer = 1,.pipe_bof = 1,},
191 		.bufsize = G_AUDIO_BUFSIZE,
192 		.callback = &g_audio_isoc_write_callback,
193 		.frames = G_AUDIO_FRAMES,
194 		.usb_mode = USB_MODE_DEVICE,
195 		.if_index = 2,
196 	},
197 
198 	[G_AUDIO_ISOC1_WR] = {
199 		.type = UE_ISOCHRONOUS,
200 		.endpoint = UE_ADDR_ANY,
201 		.direction = UE_DIR_TX,
202 		.flags = {.ext_buffer = 1,.pipe_bof = 1,},
203 		.bufsize = G_AUDIO_BUFSIZE,
204 		.callback = &g_audio_isoc_write_callback,
205 		.frames = G_AUDIO_FRAMES,
206 		.usb_mode = USB_MODE_DEVICE,
207 		.if_index = 2,
208 	},
209 };
210 
211 static void
212 g_audio_timeout_reset(struct g_audio_softc *sc)
213 {
214 	int i = g_audio_pattern_interval;
215 
216 	sc->sc_tx_interval = i;
217 
218 	if (i <= 0)
219 		i = 1;
220 	else if (i > 1023)
221 		i = 1023;
222 
223 	i = USB_MS_TO_TICKS(i);
224 
225 	usb_callout_reset(&sc->sc_callout, i, &g_audio_timeout, sc);
226 }
227 
228 static void
229 g_audio_timeout(void *arg)
230 {
231 	struct g_audio_softc *sc = arg;
232 
233 	sc->sc_mode = g_audio_mode;
234 
235 	memcpy(sc->sc_pattern, g_audio_pattern_data, sizeof(sc->sc_pattern));
236 
237 	sc->sc_pattern[G_AUDIO_MAX_STRLEN - 1] = 0;
238 
239 	sc->sc_pattern_len = strlen(sc->sc_pattern);
240 
241 	if (sc->sc_mode != G_AUDIO_MODE_LOOP) {
242 		usbd_transfer_start(sc->sc_xfer[G_AUDIO_ISOC0_WR]);
243 		usbd_transfer_start(sc->sc_xfer[G_AUDIO_ISOC1_WR]);
244 	}
245 	g_audio_timeout_reset(sc);
246 }
247 
248 static void
249 g_audio_watchdog_reset(struct g_audio_softc *sc)
250 {
251 	usb_callout_reset(&sc->sc_watchdog, hz, &g_audio_watchdog, sc);
252 }
253 
254 static void
255 g_audio_watchdog(void *arg)
256 {
257 	struct g_audio_softc *sc = arg;
258 	int i;
259 
260 	i = sc->sc_throughput;
261 
262 	sc->sc_throughput = 0;
263 
264 	g_audio_throughput = i;
265 
266 	g_audio_watchdog_reset(sc);
267 }
268 
269 static int
270 g_audio_probe(device_t dev)
271 {
272 	struct usb_attach_arg *uaa = device_get_ivars(dev);
273 
274 	DPRINTFN(11, "\n");
275 
276 	if (uaa->usb_mode != USB_MODE_DEVICE)
277 		return (ENXIO);
278 
279 	if ((uaa->info.bInterfaceClass == UICLASS_AUDIO) &&
280 	    (uaa->info.bInterfaceSubClass == UISUBCLASS_AUDIOCONTROL))
281 		return (0);
282 
283 	return (ENXIO);
284 }
285 
286 static int
287 g_audio_attach(device_t dev)
288 {
289 	struct g_audio_softc *sc = device_get_softc(dev);
290 	struct usb_attach_arg *uaa = device_get_ivars(dev);
291 	int error;
292 	int i;
293 	uint8_t iface_index[3];
294 
295 	DPRINTFN(11, "\n");
296 
297 	device_set_usb_desc(dev);
298 
299 	mtx_init(&sc->sc_mtx, "g_audio", NULL, MTX_DEF);
300 
301 	usb_callout_init_mtx(&sc->sc_callout, &sc->sc_mtx, 0);
302 	usb_callout_init_mtx(&sc->sc_watchdog, &sc->sc_mtx, 0);
303 
304 	sc->sc_mode = G_AUDIO_MODE_SILENT;
305 
306 	sc->sc_noise_rem = 1;
307 
308 	for (i = 0; i != G_AUDIO_FRAMES; i++) {
309 		sc->sc_data_len[0][i] = G_AUDIO_BUFSIZE / G_AUDIO_FRAMES;
310 		sc->sc_data_len[1][i] = G_AUDIO_BUFSIZE / G_AUDIO_FRAMES;
311 	}
312 
313 	iface_index[0] = uaa->info.bIfaceIndex;
314 	iface_index[1] = uaa->info.bIfaceIndex + 1;
315 	iface_index[2] = uaa->info.bIfaceIndex + 2;
316 
317 	error = usbd_set_alt_interface_index(uaa->device, iface_index[1], 1);
318 	if (error) {
319 		DPRINTF("alt iface setting error=%s\n", usbd_errstr(error));
320 		goto detach;
321 	}
322 	error = usbd_set_alt_interface_index(uaa->device, iface_index[2], 1);
323 	if (error) {
324 		DPRINTF("alt iface setting error=%s\n", usbd_errstr(error));
325 		goto detach;
326 	}
327 	error = usbd_transfer_setup(uaa->device,
328 	    iface_index, sc->sc_xfer, g_audio_config,
329 	    G_AUDIO_N_TRANSFER, sc, &sc->sc_mtx);
330 
331 	if (error) {
332 		DPRINTF("error=%s\n", usbd_errstr(error));
333 		goto detach;
334 	}
335 	usbd_set_parent_iface(uaa->device, iface_index[1], iface_index[0]);
336 	usbd_set_parent_iface(uaa->device, iface_index[2], iface_index[0]);
337 
338 	mtx_lock(&sc->sc_mtx);
339 
340 	usbd_transfer_start(sc->sc_xfer[G_AUDIO_ISOC0_RD]);
341 	usbd_transfer_start(sc->sc_xfer[G_AUDIO_ISOC1_RD]);
342 
343 	usbd_transfer_start(sc->sc_xfer[G_AUDIO_ISOC0_WR]);
344 	usbd_transfer_start(sc->sc_xfer[G_AUDIO_ISOC1_WR]);
345 
346 	g_audio_timeout_reset(sc);
347 
348 	g_audio_watchdog_reset(sc);
349 
350 	mtx_unlock(&sc->sc_mtx);
351 
352 	return (0);			/* success */
353 
354 detach:
355 	g_audio_detach(dev);
356 
357 	return (ENXIO);			/* error */
358 }
359 
360 static int
361 g_audio_detach(device_t dev)
362 {
363 	struct g_audio_softc *sc = device_get_softc(dev);
364 
365 	DPRINTF("\n");
366 
367 	mtx_lock(&sc->sc_mtx);
368 	usb_callout_stop(&sc->sc_callout);
369 	usb_callout_stop(&sc->sc_watchdog);
370 	mtx_unlock(&sc->sc_mtx);
371 
372 	usbd_transfer_unsetup(sc->sc_xfer, G_AUDIO_N_TRANSFER);
373 
374 	usb_callout_drain(&sc->sc_callout);
375 	usb_callout_drain(&sc->sc_watchdog);
376 
377 	mtx_destroy(&sc->sc_mtx);
378 
379 	return (0);
380 }
381 
382 
383 static int32_t
384 g_noise(struct g_audio_softc *sc)
385 {
386 	uint32_t temp;
387 	const uint32_t prime = 0xFFFF1D;
388 
389 	if (sc->sc_noise_rem & 1) {
390 		sc->sc_noise_rem += prime;
391 	}
392 	sc->sc_noise_rem /= 2;
393 
394 	temp = sc->sc_noise_rem;
395 
396 	/* unsigned to signed conversion */
397 
398 	temp ^= 0x800000;
399 	if (temp & 0x800000) {
400 		temp |= (-0x800000);
401 	}
402 	return temp;
403 }
404 
405 static void
406 g_audio_make_samples(struct g_audio_softc *sc, int16_t *ptr, int samples)
407 {
408 	int i;
409 	int j;
410 
411 	for (i = 0; i != samples; i++) {
412 
413 		j = g_noise(sc);
414 
415 		if ((sc->sc_state < 0) || (sc->sc_state >= sc->sc_pattern_len))
416 			sc->sc_state = 0;
417 
418 		if (sc->sc_pattern_len != 0) {
419 			j = (j * sc->sc_pattern[sc->sc_state]) >> 16;
420 			sc->sc_state++;
421 		}
422 		*ptr++ = j / 256;
423 		*ptr++ = j / 256;
424 	}
425 }
426 
427 static void
428 g_audio_isoc_write_callback(struct usb_xfer *xfer, usb_error_t error)
429 {
430 	struct g_audio_softc *sc = usbd_xfer_softc(xfer);
431 	int actlen;
432 	int aframes;
433 	int nr = (xfer == sc->sc_xfer[G_AUDIO_ISOC0_WR]) ? 0 : 1;
434 	int16_t *ptr;
435 	int i;
436 
437 	usbd_xfer_status(xfer, &actlen, NULL, &aframes, NULL);
438 
439 	DPRINTF("st=%d aframes=%d actlen=%d bytes\n",
440 	    USB_GET_STATE(xfer), aframes, actlen);
441 
442 	switch (USB_GET_STATE(xfer)) {
443 	case USB_ST_TRANSFERRED:
444 
445 		sc->sc_throughput += actlen;
446 
447 		if (sc->sc_mode == G_AUDIO_MODE_LOOP)
448 			break;		/* sync with RX */
449 
450 	case USB_ST_SETUP:
451 tr_setup:
452 
453 		ptr = sc->sc_data_buf[nr];
454 
455 		if (sc->sc_mode == G_AUDIO_MODE_PATTERN) {
456 
457 			for (i = 0; i != G_AUDIO_FRAMES; i++) {
458 
459 				usbd_xfer_set_frame_data(xfer, i, ptr, sc->sc_data_len[nr][i]);
460 
461 				g_audio_make_samples(sc, ptr, (G_AUDIO_BUFSIZE / G_AUDIO_FRAMES) / 2);
462 
463 				ptr += (G_AUDIO_BUFSIZE / G_AUDIO_FRAMES) / 2;
464 			}
465 		} else if (sc->sc_mode == G_AUDIO_MODE_LOOP) {
466 
467 			for (i = 0; i != G_AUDIO_FRAMES; i++) {
468 
469 				usbd_xfer_set_frame_data(xfer, i, ptr, sc->sc_data_len[nr][i] & ~3);
470 
471 				g_audio_make_samples(sc, ptr, sc->sc_data_len[nr][i] / 4);
472 
473 				ptr += (G_AUDIO_BUFSIZE / G_AUDIO_FRAMES) / 2;
474 			}
475 		}
476 		break;
477 
478 	default:			/* Error */
479 		DPRINTF("error=%s\n", usbd_errstr(error));
480 
481 		if (error != USB_ERR_CANCELLED) {
482 			/* try to clear stall first */
483 			usbd_xfer_set_stall(xfer);
484 			goto tr_setup;
485 		}
486 		break;
487 	}
488 }
489 
490 static void
491 g_audio_isoc_read_callback(struct usb_xfer *xfer, usb_error_t error)
492 {
493 	struct g_audio_softc *sc = usbd_xfer_softc(xfer);
494 	int actlen;
495 	int aframes;
496 	int nr = (xfer == sc->sc_xfer[G_AUDIO_ISOC0_RD]) ? 0 : 1;
497 	int16_t *ptr;
498 	int i;
499 
500 	usbd_xfer_status(xfer, &actlen, NULL, &aframes, NULL);
501 
502 	DPRINTF("st=%d aframes=%d actlen=%d bytes\n",
503 	    USB_GET_STATE(xfer), aframes, actlen);
504 
505 	switch (USB_GET_STATE(xfer)) {
506 	case USB_ST_TRANSFERRED:
507 
508 		sc->sc_throughput += actlen;
509 
510 		for (i = 0; i != G_AUDIO_FRAMES; i++) {
511 			sc->sc_data_len[nr][i] = usbd_xfer_frame_len(xfer, i);
512 		}
513 
514 		usbd_transfer_start(sc->sc_xfer[G_AUDIO_ISOC0_WR]);
515 		usbd_transfer_start(sc->sc_xfer[G_AUDIO_ISOC1_WR]);
516 
517 		break;
518 
519 	case USB_ST_SETUP:
520 tr_setup:
521 		ptr = sc->sc_data_buf[nr];
522 
523 		for (i = 0; i != G_AUDIO_FRAMES; i++) {
524 
525 			usbd_xfer_set_frame_data(xfer, i, ptr,
526 			    G_AUDIO_BUFSIZE / G_AUDIO_FRAMES);
527 
528 			ptr += (G_AUDIO_BUFSIZE / G_AUDIO_FRAMES) / 2;
529 		}
530 
531 		usbd_transfer_submit(xfer);
532 		break;
533 
534 	default:			/* Error */
535 		DPRINTF("error=%s\n", usbd_errstr(error));
536 
537 		if (error != USB_ERR_CANCELLED) {
538 			/* try to clear stall first */
539 			usbd_xfer_set_stall(xfer);
540 			goto tr_setup;
541 		}
542 		break;
543 	}
544 }
545 
546 
547 static int
548 g_audio_handle_request(device_t dev,
549     const void *preq, void **pptr, uint16_t *plen,
550     uint16_t offset, uint8_t *pstate)
551 {
552 	struct g_audio_softc *sc = device_get_softc(dev);
553 	const struct usb_device_request *req = preq;
554 	uint8_t is_complete = *pstate;
555 
556 	if (!is_complete) {
557 		if ((req->bmRequestType == UT_READ_CLASS_INTERFACE) &&
558 		    (req->bRequest == 0x82 /* get min */ )) {
559 
560 			if (offset == 0) {
561 				USETW(sc->sc_volume_limit, 0);
562 				*plen = 2;
563 				*pptr = &sc->sc_volume_limit;
564 			} else {
565 				*plen = 0;
566 			}
567 			return (0);
568 		} else if ((req->bmRequestType == UT_READ_CLASS_INTERFACE) &&
569 		    (req->bRequest == 0x83 /* get max */ )) {
570 
571 			if (offset == 0) {
572 				USETW(sc->sc_volume_limit, 0x2000);
573 				*plen = 2;
574 				*pptr = &sc->sc_volume_limit;
575 			} else {
576 				*plen = 0;
577 			}
578 			return (0);
579 		} else if ((req->bmRequestType == UT_READ_CLASS_INTERFACE) &&
580 		    (req->bRequest == 0x84 /* get residue */ )) {
581 
582 			if (offset == 0) {
583 				USETW(sc->sc_volume_limit, 1);
584 				*plen = 2;
585 				*pptr = &sc->sc_volume_limit;
586 			} else {
587 				*plen = 0;
588 			}
589 			return (0);
590 		} else if ((req->bmRequestType == UT_READ_CLASS_INTERFACE) &&
591 		    (req->bRequest == 0x81 /* get value */ )) {
592 
593 			if (offset == 0) {
594 				USETW(sc->sc_volume_setting, 0x2000);
595 				*plen = sizeof(sc->sc_volume_setting);
596 				*pptr = &sc->sc_volume_setting;
597 			} else {
598 				*plen = 0;
599 			}
600 			return (0);
601 		} else if ((req->bmRequestType == UT_WRITE_CLASS_INTERFACE) &&
602 		    (req->bRequest == 0x01 /* set value */ )) {
603 
604 			if (offset == 0) {
605 				*plen = sizeof(sc->sc_volume_setting);
606 				*pptr = &sc->sc_volume_setting;
607 			} else {
608 				*plen = 0;
609 			}
610 			return (0);
611 		} else if ((req->bmRequestType == UT_WRITE_CLASS_ENDPOINT) &&
612 		    (req->bRequest == 0x01 /* set value */ )) {
613 
614 			if (offset == 0) {
615 				*plen = sizeof(sc->sc_sample_rate);
616 				*pptr = &sc->sc_sample_rate;
617 			} else {
618 				*plen = 0;
619 			}
620 			return (0);
621 		}
622 	}
623 	return (ENXIO);			/* use builtin handler */
624 }
625