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ALSA: rawmidi: Add framing mode

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This commit adds a new framing mode that frames all MIDI data into
32-byte frames with a timestamp.

The main benefit is that we can get accurate timestamps even if
userspace wakeup and processing is not immediate.

Testing on a Celeron N3150 with this mode has a max jitter of 2.8 ms,
compared to the in-kernel seq implementation which has a max jitter
of 5 ms during idle and much worse when running scheduler stress tests
in parallel.

Signed-off-by: David Henningsson <coding@diwic.se>
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20210515071533.55332-1-coding@diwic.se
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
David Henningsson
2021-05-15 09:15:33 +02:00
committed by Takashi Iwai
parent bac5905454
commit 08fdced60c
4 changed files with 124 additions and 5 deletions
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30
include/uapi/sound/asound.h
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@@ -710,7 +710,7 @@ enum {
* Raw MIDI section - /dev/snd/midi??
*/
#define SNDRV_RAWMIDI_VERSION SNDRV_PROTOCOL_VERSION(2, 0, 1)
#define SNDRV_RAWMIDI_VERSION SNDRV_PROTOCOL_VERSION(2, 0, 2)
enum {
SNDRV_RAWMIDI_STREAM_OUTPUT = 0,
@@ -736,12 +736,38 @@ struct snd_rawmidi_info {
unsigned char reserved[64]; /* reserved for future use */
};
#define SNDRV_RAWMIDI_MODE_FRAMING_MASK (7<<0)
#define SNDRV_RAWMIDI_MODE_FRAMING_SHIFT 0
#define SNDRV_RAWMIDI_MODE_FRAMING_NONE (0<<0)
#define SNDRV_RAWMIDI_MODE_FRAMING_TSTAMP (1<<0)
#define SNDRV_RAWMIDI_MODE_CLOCK_MASK (7<<3)
#define SNDRV_RAWMIDI_MODE_CLOCK_SHIFT 3
#define SNDRV_RAWMIDI_MODE_CLOCK_NONE (0<<3)
#define SNDRV_RAWMIDI_MODE_CLOCK_REALTIME (1<<3)
#define SNDRV_RAWMIDI_MODE_CLOCK_MONOTONIC (2<<3)
#define SNDRV_RAWMIDI_MODE_CLOCK_MONOTONIC_RAW (3<<3)
#define SNDRV_RAWMIDI_FRAMING_DATA_LENGTH 16
struct snd_rawmidi_framing_tstamp {
/* For now, frame_type is always 0. Midi 2.0 is expected to add new
* types here. Applications are expected to skip unknown frame types.
*/
__u8 frame_type;
__u8 length; /* number of valid bytes in data field */
__u8 reserved[2];
__u32 tv_nsec; /* nanoseconds */
__u64 tv_sec; /* seconds */
__u8 data[SNDRV_RAWMIDI_FRAMING_DATA_LENGTH];
} __packed;
struct snd_rawmidi_params {
int stream;
size_t buffer_size; /* queue size in bytes */
size_t avail_min; /* minimum avail bytes for wakeup */
unsigned int no_active_sensing: 1; /* do not send active sensing byte in close() */
unsigned char reserved[16]; /* reserved for future use */
unsigned int mode; /* For input data only, frame incoming data */
unsigned char reserved[12]; /* reserved for future use */
};
#ifndef __KERNEL__