Dne 10. 04. 21 v 14:02 David Henningsson napsal(a):
> 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@xxxxxxxx>
> ---
> include/sound/rawmidi.h | 2 ++
> include/uapi/sound/asound.h | 26 ++++++++++++++--
> sound/core/rawmidi.c | 60 +++++++++++++++++++++++++++++++++++--
> 3 files changed, 84 insertions(+), 4 deletions(-)
>
> diff --git a/include/sound/rawmidi.h b/include/sound/rawmidi.h
> index 334842daa904..b0057a193c31 100644
> --- a/include/sound/rawmidi.h
> +++ b/include/sound/rawmidi.h
> @@ -81,6 +81,8 @@ struct snd_rawmidi_substream {
> bool opened; /* open flag */
> bool append; /* append flag (merge more streams) */
> bool active_sensing; /* send active sensing when close */
> + u8 framing; /* whether to frame input data */
> + clockid_t clock_type; /* clock source to use for input framing */
> int use_count; /* use counter (for output) */
> size_t bytes;
> struct snd_rawmidi *rmidi;
> diff --git a/include/uapi/sound/asound.h b/include/uapi/sound/asound.h
> index 535a7229e1d9..af8e60740218 100644
> --- a/include/uapi/sound/asound.h
> +++ b/include/uapi/sound/asound.h
> @@ -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 +736,34 @@ struct snd_rawmidi_info {
> unsigned char reserved[64]; /* reserved for future use */
> };
>
> +enum {
> + SNDRV_RAWMIDI_FRAMING_NONE = 0,
> + SNDRV_RAWMIDI_FRAMING_TSTAMP,
> + SNDRV_RAWMIDI_FRAMING_LAST = SNDRV_RAWMIDI_FRAMING_TSTAMP,
> +};
> +
> +#define SND_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.
> + */
> + unsigned char frame_type;
> + unsigned char length; /* number of valid bytes in data field */
> + unsigned char reserved[2];
> + unsigned int tv_nsec; /* nanoseconds */
> + unsigned long long tv_sec; /* seconds */
> + unsigned char data[SND_RAWMIDI_FRAMING_DATA_LENGTH];
> +};
> +
> 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 char framing; /* For input data only, frame incoming data */
We can move this flag to above 32-bit word (no_active_sensing). I'm not sure,
if we need 8 bits for this. It's first change after 20 years. Another flag may
obsolete this one.
> + unsigned char clock_type; /* Type of clock to use for framing, same as clockid_t */
> + unsigned char reserved[14]; /* reserved for future use */
> };
>
> #ifndef __KERNEL__
> diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
> index aca00af93afe..d4b6b9b5c0e4 100644
> --- a/sound/core/rawmidi.c
> +++ b/sound/core/rawmidi.c
> @@ -683,6 +683,8 @@ static int resize_runtime_buffer(struct snd_rawmidi_runtime *runtime,
>
> if (params->buffer_size < 32 || params->buffer_size > 1024L * 1024L)
> return -EINVAL;
> + if (params->framing == SNDRV_RAWMIDI_FRAMING_TSTAMP && params->buffer_size & 0x1f)
I would use '(a & b) != 0' here. It's more readable.
> + return -EINVAL;
> if (params->avail_min < 1 || params->avail_min > params->buffer_size)
> return -EINVAL;
> if (params->buffer_size != runtime->buffer_size) {
> @@ -720,7 +722,16 @@ EXPORT_SYMBOL(snd_rawmidi_output_params);
> int snd_rawmidi_input_params(struct snd_rawmidi_substream *substream,
> struct snd_rawmidi_params *params)
> {
> + if (params->framing) {
> + if (params->framing > SNDRV_RAWMIDI_FRAMING_LAST)
> + return -EINVAL;
> + /* framing requires a valid clock type */
> + if (params->clock_type != CLOCK_MONOTONIC_RAW && params->clock_type != CLOCK_MONOTONIC)
> + return -EINVAL;
The CLOCK_REALTIME may be supported, too. For example, the input subsystem
supports those three timestamps and we support this in the PCM interface, too.
> + }
> snd_rawmidi_drain_input(substream);
> + substream->framing = params->framing;
> + substream->clock_type = params->clock_type;
> return resize_runtime_buffer(substream->runtime, params, true);
> }
> EXPORT_SYMBOL(snd_rawmidi_input_params);
> @@ -963,6 +974,42 @@ static int snd_rawmidi_control_ioctl(struct snd_card *card,
> return -ENOIOCTLCMD;
> }
>
> +static int receive_with_tstamp_framing(struct snd_rawmidi_substream *substream,
> + const unsigned char *buffer, int src_count, struct timespec64 *tstamp)
> +{
> + struct snd_rawmidi_runtime *runtime = substream->runtime;
> + struct snd_rawmidi_framing_tstamp *dest_ptr;
> + struct snd_rawmidi_framing_tstamp frame = { .tv_sec = tstamp->tv_sec, .tv_nsec = tstamp->tv_nsec };
> +
> + int dest_frames = 0;
> + int frame_size = sizeof(struct snd_rawmidi_framing_tstamp);
> +
> + if (snd_BUG_ON(runtime->hw_ptr & 0x1f || runtime->buffer_size & 0x1f || frame_size != 0x20))
> + return -EINVAL;
> + while (src_count > 0) {
> + if ((int)(runtime->buffer_size - runtime->avail) < frame_size) {
> + runtime->xruns += src_count;
> + return dest_frames * frame_size;
> + }
> + if (src_count >= SND_RAWMIDI_FRAMING_DATA_LENGTH)
> + frame.length = SND_RAWMIDI_FRAMING_DATA_LENGTH;
> + else {
> + frame.length = src_count;
> + memset(frame.data, 0, SND_RAWMIDI_FRAMING_DATA_LENGTH);
We know the length here, so we can skip the zeroing the copied bytes with
memcpy().
Jaroslav
--
Jaroslav Kysela <perex@xxxxxxxx>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
