linux/sound/usb/endpoint.h
Alexander Tsoy f0bd62b640 ALSA: usb-audio: Improve frames size computation
For computation of the the next frame size current value of fs/fps and
accumulated fractional parts of fs/fps are used, where values are stored
in Q16.16 format. This is quite natural for computing frame size for
asynchronous endpoints driven by explicit feedback, since in this case
fs/fps is a value provided by the feedback endpoint and it's already in
the Q format. If an error is accumulated over time, the device can
adjust fs/fps value to prevent buffer overruns/underruns.

But for synchronous endpoints the accuracy provided by these computations
is not enough. Due to accumulated error the driver periodically produces
frames with incorrect size (+/- 1 audio sample).

This patch fixes this issue by implementing a different algorithm for
frame size computation. It is based on accumulating of the remainders
from division fs/fps and it doesn't accumulate errors over time. This
new method is enabled for synchronous and adaptive playback endpoints.

Signed-off-by: Alexander Tsoy <alexander@tsoy.me>
Link: https://lore.kernel.org/r/20200424022449.14972-1-alexander@tsoy.me
Signed-off-by: Takashi Iwai <tiwai@suse.de>
2020-04-24 08:25:24 +02:00

39 lines
1.4 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __USBAUDIO_ENDPOINT_H
#define __USBAUDIO_ENDPOINT_H
#define SND_USB_ENDPOINT_TYPE_DATA 0
#define SND_USB_ENDPOINT_TYPE_SYNC 1
struct snd_usb_endpoint *snd_usb_add_endpoint(struct snd_usb_audio *chip,
struct usb_host_interface *alts,
int ep_num, int direction, int type);
int snd_usb_endpoint_set_params(struct snd_usb_endpoint *ep,
snd_pcm_format_t pcm_format,
unsigned int channels,
unsigned int period_bytes,
unsigned int period_frames,
unsigned int buffer_periods,
unsigned int rate,
struct audioformat *fmt,
struct snd_usb_endpoint *sync_ep);
int snd_usb_endpoint_start(struct snd_usb_endpoint *ep);
void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep);
void snd_usb_endpoint_sync_pending_stop(struct snd_usb_endpoint *ep);
int snd_usb_endpoint_activate(struct snd_usb_endpoint *ep);
void snd_usb_endpoint_deactivate(struct snd_usb_endpoint *ep);
void snd_usb_endpoint_release(struct snd_usb_endpoint *ep);
void snd_usb_endpoint_free(struct snd_usb_endpoint *ep);
int snd_usb_endpoint_implicit_feedback_sink(struct snd_usb_endpoint *ep);
int snd_usb_endpoint_slave_next_packet_size(struct snd_usb_endpoint *ep);
int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep);
void snd_usb_handle_sync_urb(struct snd_usb_endpoint *ep,
struct snd_usb_endpoint *sender,
const struct urb *urb);
#endif /* __USBAUDIO_ENDPOINT_H */