[alsa-devel] [RFC - AAF PCM plugin 3/5] aaf: Implement Playback mode support
Andre Guedes
andre.guedes at intel.com
Tue Aug 21 03:06:51 CEST 2018
This patch implements the playback mode support from the AAF plugin.
Simply put, this mode works as follows: PCM samples provided by alsa-lib
layer are encapsulated into AVTP packets and transmitted through the
network. In summary, the playback mode implements a typical AVTP Talker.
When the AAF device is put in running state, its media clock is started.
At every tick from the media clock, audio frames are consumed from the
audio buffer, encapsulated into an AVTP packet, and transmitted to the
network. The presentation time from each AVTP packet is calculated
taking in consideration the maximum transit time and time uncertainty
values configured by the user.
Below follows some discussion about implementation details:
Even though only one file descriptor is used to implement the playback
mode, this patch doesn't leverage ioplug->poll_fd but defines poll
callbacks instead. The reason is these callbacks will be required to
support capture mode (to be implemented by upcoming patch).
The TSN data plane interface is the AF_PACKET socket family so the
plugin uses an AF_PACKET socket to send/receive AVTP packets. Linux
requires CAP_NET_RAW capability in order to open an AF_PACKET socket so
the application that instantiates the plugin must have it. For further
info about AF_PACKET socket family see packet(7).
Signed-off-by: Andre Guedes <andre.guedes at intel.com>
---
aaf/pcm_aaf.c | 611 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
doc/aaf.txt | 40 ++++
2 files changed, 651 insertions(+)
diff --git a/aaf/pcm_aaf.c b/aaf/pcm_aaf.c
index 4c6f031..72f6652 100644
--- a/aaf/pcm_aaf.c
+++ b/aaf/pcm_aaf.c
@@ -20,13 +20,30 @@
#include <alsa/asoundlib.h>
#include <alsa/pcm_external.h>
+#include <arpa/inet.h>
+#include <avtp.h>
+#include <avtp_aaf.h>
+#include <limits.h>
#include <linux/if.h>
#include <linux/if_ether.h>
+#include <linux/if_packet.h>
#include <string.h>
#include <stdint.h>
+#include <sys/ioctl.h>
+#include <sys/timerfd.h>
+#ifdef AAF_DEBUG
+#define pr_debug(...) SNDERR(__VA_ARGS__)
+#else
+#define pr_debug(...) (void)0
+#endif
+
+#define CLOCK_REF CLOCK_REALTIME
+#define NSEC_PER_SEC 1000000000ULL
#define NSEC_PER_USEC 1000ULL
+#define FD_COUNT_PLAYBACK 1
+
typedef struct {
snd_pcm_ioplug_t io;
@@ -37,8 +54,74 @@ typedef struct {
int mtt;
int t_uncertainty;
int frames_per_pkt;
+
+ int sk_fd;
+ int timer_fd;
+
+ struct sockaddr_ll sk_addr;
+
+ char *audiobuf;
+
+ struct avtp_stream_pdu *pdu;
+ int pdu_size;
+ uint8_t pdu_seq;
+
+ uint64_t mclk_start_time;
+ uint64_t mclk_period;
+ uint64_t mclk_ticks;
+
+ snd_pcm_channel_area_t *audiobuf_areas;
+ snd_pcm_channel_area_t *payload_areas;
+
+ snd_pcm_sframes_t hw_ptr;
+ snd_pcm_sframes_t buffer_size;
+ snd_pcm_sframes_t boundary;
} snd_pcm_aaf_t;
+static unsigned int alsa_to_avtp_format(snd_pcm_format_t format)
+{
+ switch (format) {
+ case SND_PCM_FORMAT_S16_BE:
+ return AVTP_AAF_FORMAT_INT_16BIT;
+ case SND_PCM_FORMAT_S24_3BE:
+ return AVTP_AAF_FORMAT_INT_24BIT;
+ case SND_PCM_FORMAT_S32_BE:
+ return AVTP_AAF_FORMAT_INT_32BIT;
+ case SND_PCM_FORMAT_FLOAT_BE:
+ return AVTP_AAF_FORMAT_FLOAT_32BIT;
+ default:
+ return AVTP_AAF_FORMAT_USER;
+ }
+}
+
+static unsigned int alsa_to_avtp_rate(unsigned int rate)
+{
+ switch (rate) {
+ case 8000:
+ return AVTP_AAF_PCM_NSR_8KHZ;
+ case 16000:
+ return AVTP_AAF_PCM_NSR_16KHZ;
+ case 24000:
+ return AVTP_AAF_PCM_NSR_24KHZ;
+ case 32000:
+ return AVTP_AAF_PCM_NSR_32KHZ;
+ case 44100:
+ return AVTP_AAF_PCM_NSR_44_1KHZ;
+ case 48000:
+ return AVTP_AAF_PCM_NSR_48KHZ;
+ case 88200:
+ return AVTP_AAF_PCM_NSR_88_2KHZ;
+ case 96000:
+ return AVTP_AAF_PCM_NSR_96KHZ;
+ case 176400:
+ return AVTP_AAF_PCM_NSR_176_4KHZ;
+ case 192000:
+ return AVTP_AAF_PCM_NSR_192KHZ;
+ default:
+ return AVTP_AAF_PCM_NSR_USER;
+ }
+}
+
static int aaf_load_config(snd_pcm_aaf_t *aaf, snd_config_t *conf)
{
snd_config_iterator_t cur, next;
@@ -147,6 +230,327 @@ err:
return -EINVAL;
}
+static int aaf_init_socket(snd_pcm_aaf_t *aaf)
+{
+ int fd, res;
+ struct ifreq req;
+
+ fd = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_TSN));
+ if (fd < 0) {
+ SNDERR("Failed to open AF_PACKET socket");
+ return -errno;
+ }
+
+ snprintf(req.ifr_name, sizeof(req.ifr_name), "%s", aaf->ifname);
+ res = ioctl(fd, SIOCGIFINDEX, &req);
+ if (res < 0) {
+ SNDERR("Failed to get network interface index");
+ res = -errno;
+ goto err;
+ }
+
+ aaf->sk_addr.sll_family = AF_PACKET;
+ aaf->sk_addr.sll_protocol = htons(ETH_P_TSN);
+ aaf->sk_addr.sll_halen = ETH_ALEN;
+ aaf->sk_addr.sll_ifindex = req.ifr_ifindex;
+ memcpy(&aaf->sk_addr.sll_addr, aaf->addr, ETH_ALEN);
+
+ res = setsockopt(fd, SOL_SOCKET, SO_PRIORITY, &aaf->prio,
+ sizeof(aaf->prio));
+ if (res < 0) {
+ SNDERR("Failed to set socket priority");
+ res = -errno;
+ goto err;
+ }
+
+ aaf->sk_fd = fd;
+ return 0;
+
+err:
+ close(fd);
+ return res;
+}
+
+static int aaf_init_timer(snd_pcm_aaf_t *aaf)
+{
+ int fd;
+
+ fd = timerfd_create(CLOCK_REF, 0);
+ if (fd < 0)
+ return -errno;
+
+ aaf->timer_fd = fd;
+ return 0;
+}
+
+static int aaf_init_pdu(snd_pcm_aaf_t *aaf)
+{
+ int res;
+ struct avtp_stream_pdu *pdu;
+ ssize_t frame_size, payload_size, pdu_size;
+ snd_pcm_ioplug_t *io = &aaf->io;
+
+ frame_size = snd_pcm_format_size(io->format, io->channels);
+ if (frame_size < 0)
+ return frame_size;
+
+ payload_size = frame_size * aaf->frames_per_pkt;
+ pdu_size = sizeof(*pdu) + payload_size;
+ pdu = calloc(1, pdu_size);
+ if (!pdu)
+ return -ENOMEM;
+
+ res = avtp_aaf_pdu_init(pdu);
+ if (res < 0)
+ goto err;
+
+ res = avtp_aaf_pdu_set(pdu, AVTP_AAF_FIELD_TV, 1);
+ if (res < 0)
+ goto err;
+
+ res = avtp_aaf_pdu_set(pdu, AVTP_AAF_FIELD_STREAM_ID, aaf->streamid);
+ if (res < 0)
+ goto err;
+
+ res = avtp_aaf_pdu_set(pdu, AVTP_AAF_FIELD_FORMAT,
+ alsa_to_avtp_format(io->format));
+ if (res < 0)
+ goto err;
+
+ res = avtp_aaf_pdu_set(pdu, AVTP_AAF_FIELD_NSR,
+ alsa_to_avtp_rate(io->rate));
+ if (res < 0)
+ goto err;
+
+ res = avtp_aaf_pdu_set(pdu, AVTP_AAF_FIELD_CHAN_PER_FRAME,
+ io->channels);
+ if (res < 0)
+ goto err;
+
+ res = avtp_aaf_pdu_set(pdu, AVTP_AAF_FIELD_BIT_DEPTH,
+ snd_pcm_format_width(io->format));
+ if (res < 0)
+ goto err;
+
+ res = avtp_aaf_pdu_set(pdu, AVTP_AAF_FIELD_STREAM_DATA_LEN,
+ payload_size);
+ if (res < 0)
+ goto err;
+
+ res = avtp_aaf_pdu_set(pdu, AVTP_AAF_FIELD_SP, AVTP_AAF_PCM_SP_NORMAL);
+ if (res < 0)
+ goto err;
+
+ aaf->pdu = pdu;
+ aaf->pdu_size = pdu_size;
+ aaf->pdu_seq = 0;
+ return 0;
+
+err:
+ free(pdu);
+ return res;
+}
+
+static int aaf_init_audio_buffer(snd_pcm_aaf_t *aaf)
+{
+ char *audiobuf;
+ ssize_t frame_size, audiobuf_size;
+ snd_pcm_ioplug_t *io = &aaf->io;
+
+ frame_size = snd_pcm_format_size(io->format, io->channels);
+ if (frame_size < 0)
+ return frame_size;
+
+ audiobuf_size = frame_size * aaf->buffer_size;
+ audiobuf = calloc(1, audiobuf_size);
+ if (!audiobuf)
+ return -ENOMEM;
+
+ aaf->audiobuf = audiobuf;
+ return 0;
+}
+
+static int aaf_init_areas(snd_pcm_aaf_t *aaf)
+{
+ snd_pcm_channel_area_t *audiobuf_areas, *payload_areas;
+ ssize_t sample_size, frame_size;
+ snd_pcm_ioplug_t *io = &aaf->io;
+
+ sample_size = snd_pcm_format_size(io->format, 1);
+ if (sample_size < 0)
+ return sample_size;
+
+ frame_size = sample_size * io->channels;
+
+ audiobuf_areas = calloc(io->channels, sizeof(snd_pcm_channel_area_t));
+ if (!audiobuf_areas)
+ return -ENOMEM;
+
+ payload_areas = calloc(io->channels, sizeof(snd_pcm_channel_area_t));
+ if (!payload_areas) {
+ free(audiobuf_areas);
+ return -ENOMEM;
+ }
+
+ for (unsigned int i = 0; i < io->channels; i++) {
+ audiobuf_areas[i].addr = aaf->audiobuf;
+ audiobuf_areas[i].first = i * sample_size * 8;
+ audiobuf_areas[i].step = frame_size * 8;
+
+ payload_areas[i].addr = aaf->pdu->avtp_payload;
+ payload_areas[i].first = i * sample_size * 8;
+ payload_areas[i].step = frame_size * 8;
+ }
+
+ aaf->audiobuf_areas = audiobuf_areas;
+ aaf->payload_areas = payload_areas;
+ return 0;
+}
+
+static void aaf_inc_hw_ptr(snd_pcm_aaf_t *aaf, snd_pcm_sframes_t val)
+{
+ aaf->hw_ptr += val;
+
+ if (aaf->hw_ptr >= aaf->boundary)
+ aaf->hw_ptr -= aaf->boundary;
+}
+
+static int aaf_mclk_start_playback(snd_pcm_aaf_t *aaf)
+{
+ int res;
+ struct timespec now;
+ struct itimerspec itspec;
+ snd_pcm_ioplug_t *io = &aaf->io;
+
+ res = clock_gettime(CLOCK_REF, &now);
+ if (res < 0) {
+ SNDERR("Failed to get time from clock");
+ return -errno;
+ }
+
+ aaf->mclk_period = (NSEC_PER_SEC * aaf->frames_per_pkt) / io->rate;
+ aaf->mclk_ticks = 0;
+ aaf->mclk_start_time = now.tv_sec * NSEC_PER_SEC + now.tv_nsec +
+ aaf->mclk_period;
+
+ itspec.it_value.tv_sec = aaf->mclk_start_time / NSEC_PER_SEC;
+ itspec.it_value.tv_nsec = aaf->mclk_start_time % NSEC_PER_SEC;
+ itspec.it_interval.tv_sec = 0;
+ itspec.it_interval.tv_nsec = aaf->mclk_period;
+ res = timerfd_settime(aaf->timer_fd, TFD_TIMER_ABSTIME, &itspec, NULL);
+ if (res < 0)
+ return -errno;
+
+ return 0;
+}
+
+static int aaf_mclk_reset(snd_pcm_aaf_t *aaf)
+{
+ aaf->mclk_start_time = 0;
+ aaf->mclk_period = 0;
+ aaf->mclk_ticks = 0;
+
+ if (aaf->timer_fd != -1) {
+ int res;
+ struct itimerspec itspec = { 0 };
+
+ res = timerfd_settime(aaf->timer_fd, 0, &itspec, NULL);
+ if (res < 0) {
+ SNDERR("Failed to stop media clock");
+ return res;
+ }
+ }
+
+ return 0;
+}
+
+static uint64_t aaf_mclk_gettime(snd_pcm_aaf_t *aaf)
+{
+ return aaf->mclk_start_time + aaf->mclk_period * aaf->mclk_ticks;
+}
+
+static int aaf_tx_pdu(snd_pcm_aaf_t *aaf)
+{
+ int res;
+ uint64_t ptime;
+ snd_pcm_sframes_t n;
+ snd_pcm_ioplug_t *io = &aaf->io;
+ snd_pcm_t *pcm = io->pcm;
+ struct avtp_stream_pdu *pdu = aaf->pdu;
+
+ n = aaf->buffer_size - snd_pcm_avail(pcm);
+ if (n == 0) {
+ /* If there is no data in audio buffer to be transmitted,
+ * we reached an underrun state.
+ */
+ return -EPIPE;
+ }
+ if (n < aaf->frames_per_pkt) {
+ /* If there isn't enough frames to fill the AVTP packet, we
+ * drop them. This behavior is suggested by IEEE 1722-2016
+ * spec, section 7.3.5.
+ */
+ aaf_inc_hw_ptr(aaf, n);
+ return 0;
+ }
+
+ res = snd_pcm_areas_copy_wrap(aaf->payload_areas, 0,
+ aaf->frames_per_pkt,
+ aaf->audiobuf_areas,
+ aaf->hw_ptr % aaf->buffer_size,
+ aaf->buffer_size, io->channels,
+ aaf->frames_per_pkt, io->format);
+ if (res < 0) {
+ SNDERR("Failed to copy data to AVTP payload");
+ return res;
+ }
+
+ res = avtp_aaf_pdu_set(pdu, AVTP_AAF_FIELD_SEQ_NUM, aaf->pdu_seq++);
+ if (res < 0)
+ return res;
+
+ ptime = aaf_mclk_gettime(aaf) + aaf->mtt + aaf->t_uncertainty;
+ res = avtp_aaf_pdu_set(pdu, AVTP_AAF_FIELD_TIMESTAMP, ptime);
+ if (res < 0)
+ return res;
+
+ n = sendto(aaf->sk_fd, aaf->pdu, aaf->pdu_size, 0,
+ (struct sockaddr *) &aaf->sk_addr,
+ sizeof(aaf->sk_addr));
+ if (n < 0 || n != aaf->pdu_size) {
+ SNDERR("Failed to send AAF PDU");
+ return -EIO;
+ }
+
+ aaf_inc_hw_ptr(aaf, aaf->frames_per_pkt);
+ return 0;
+}
+
+static int aaf_mclk_timeout_playback(snd_pcm_aaf_t *aaf)
+{
+ int res;
+ ssize_t n;
+ uint64_t expirations;
+
+ n = read(aaf->timer_fd, &expirations, sizeof(uint64_t));
+ if (n < 0) {
+ SNDERR("Failed to read() timer");
+ return -errno;
+ }
+
+ if (expirations != 1)
+ pr_debug("Missed %llu tx interval(s) ", expirations - 1);
+
+ while (expirations--) {
+ res = aaf_tx_pdu(aaf);
+ if (res < 0)
+ return res;
+ aaf->mclk_ticks++;
+ }
+
+ return 0;
+}
+
static int aaf_close(snd_pcm_ioplug_t *io)
{
snd_pcm_aaf_t *aaf = io->private_data;
@@ -159,26 +563,223 @@ static int aaf_close(snd_pcm_ioplug_t *io)
return 0;
}
+static int aaf_hw_params(snd_pcm_ioplug_t *io,
+ snd_pcm_hw_params_t *params ATTRIBUTE_UNUSED)
+{
+ int res;
+ snd_pcm_aaf_t *aaf = io->private_data;
+
+ if (io->access != SND_PCM_ACCESS_RW_INTERLEAVED)
+ return -ENOTSUP;
+
+ if (io->buffer_size > LONG_MAX)
+ return -EINVAL;
+
+ /* XXX: We might want to support Little Endian format in future. To
+ * achieve that, we need to convert LE samples to BE before
+ * transmitting them.
+ */
+ switch (io->format) {
+ case SND_PCM_FORMAT_S16_BE:
+ case SND_PCM_FORMAT_S24_3BE:
+ case SND_PCM_FORMAT_S32_BE:
+ case SND_PCM_FORMAT_FLOAT_BE:
+ break;
+ default:
+ return -ENOTSUP;
+ }
+
+ switch (io->rate) {
+ case 8000:
+ case 16000:
+ case 24000:
+ case 32000:
+ case 44100:
+ case 48000:
+ case 88200:
+ case 96000:
+ case 176400:
+ case 192000:
+ break;
+ default:
+ return -ENOTSUP;
+ }
+
+ aaf->buffer_size = io->buffer_size;
+
+ res = aaf_init_pdu(aaf);
+ if (res < 0)
+ return res;
+
+ res = aaf_init_audio_buffer(aaf);
+ if (res < 0)
+ goto err_free_pdu;
+
+ res = aaf_init_areas(aaf);
+ if (res < 0)
+ goto err_free_audiobuf;
+
+ return 0;
+
+err_free_audiobuf:
+ free(aaf->audiobuf);
+err_free_pdu:
+ free(aaf->pdu);
+ return res;
+}
+
+static int aaf_hw_free(snd_pcm_ioplug_t *io)
+{
+ snd_pcm_aaf_t *aaf = io->private_data;
+
+ free(aaf->audiobuf_areas);
+ free(aaf->payload_areas);
+ free(aaf->audiobuf);
+ free(aaf->pdu);
+ return 0;
+}
+
+static int aaf_sw_params(snd_pcm_ioplug_t *io, snd_pcm_sw_params_t *params)
+{
+ int res;
+ snd_pcm_uframes_t boundary;
+ snd_pcm_aaf_t *aaf = io->private_data;
+
+ res = snd_pcm_sw_params_get_boundary(params, &boundary);
+ if (res < 0)
+ return res;
+
+ if (boundary > LONG_MAX)
+ return -EINVAL;
+
+ aaf->boundary = boundary;
+ return 0;
+}
+
static snd_pcm_sframes_t aaf_pointer(snd_pcm_ioplug_t *io)
{
+ snd_pcm_aaf_t *aaf = io->private_data;
+
+ return aaf->hw_ptr;
+}
+
+static int aaf_poll_descriptors_count(snd_pcm_ioplug_t *io ATTRIBUTE_UNUSED)
+{
+ return FD_COUNT_PLAYBACK;
+}
+
+static int aaf_poll_descriptors(snd_pcm_ioplug_t *io, struct pollfd *pfd,
+ unsigned int space)
+{
+ snd_pcm_aaf_t *aaf = io->private_data;
+
+ if (space != FD_COUNT_PLAYBACK)
+ return -EINVAL;
+
+ pfd[0].fd = aaf->timer_fd;
+ pfd[0].events = POLLIN;
+ return space;
+}
+
+static int aaf_poll_revents(snd_pcm_ioplug_t *io, struct pollfd *pfd,
+ unsigned int nfds, unsigned short *revents)
+{
+ int res;
+ snd_pcm_aaf_t *aaf = io->private_data;
+
+ if (nfds != FD_COUNT_PLAYBACK)
+ return -EINVAL;
+
+ if (pfd[0].revents & POLLIN) {
+ res = aaf_mclk_timeout_playback(aaf);
+ if (res < 0)
+ return res;
+
+ *revents = POLLIN;
+ }
+
+ return 0;
+}
+
+static int aaf_prepare(snd_pcm_ioplug_t *io)
+{
+ int res;
+ snd_pcm_aaf_t *aaf = io->private_data;
+
+ aaf->hw_ptr = 0;
+ res = aaf_mclk_reset(aaf);
+ if (res < 0)
+ return res;
+
return 0;
}
static int aaf_start(snd_pcm_ioplug_t *io)
{
+ int res;
+ snd_pcm_aaf_t *aaf = io->private_data;
+
+ res = aaf_init_socket(aaf);
+ if (res < 0)
+ return res;
+
+ res = aaf_init_timer(aaf);
+ if (res < 0)
+ goto err_close_sk;
+
+ res = aaf_mclk_start_playback(aaf);
+ if (res < 0)
+ goto err_close_timer;
+
return 0;
+
+err_close_timer:
+ close(aaf->timer_fd);
+err_close_sk:
+ close(aaf->sk_fd);
+ return res;
}
static int aaf_stop(snd_pcm_ioplug_t *io)
{
+ snd_pcm_aaf_t *aaf = io->private_data;
+
+ close(aaf->timer_fd);
+ close(aaf->sk_fd);
return 0;
}
+static snd_pcm_sframes_t aaf_transfer(snd_pcm_ioplug_t *io,
+ const snd_pcm_channel_area_t *areas,
+ snd_pcm_uframes_t offset,
+ snd_pcm_uframes_t size)
+{
+ int res;
+ snd_pcm_aaf_t *aaf = io->private_data;
+
+ res = snd_pcm_areas_copy_wrap(aaf->audiobuf_areas,
+ (io->appl_ptr % aaf->buffer_size),
+ aaf->buffer_size, areas, offset, size,
+ io->channels, size, io->format);
+ if (res < 0)
+ return res;
+
+ return size;
+}
+
static const snd_pcm_ioplug_callback_t aaf_callback = {
.close = aaf_close,
+ .hw_params = aaf_hw_params,
+ .hw_free = aaf_hw_free,
+ .sw_params = aaf_sw_params,
.pointer = aaf_pointer,
+ .poll_descriptors_count = aaf_poll_descriptors_count,
+ .poll_descriptors = aaf_poll_descriptors,
+ .poll_revents = aaf_poll_revents,
+ .prepare = aaf_prepare,
.start = aaf_start,
.stop = aaf_stop,
+ .transfer = aaf_transfer,
};
SND_PCM_PLUGIN_DEFINE_FUNC(aaf)
@@ -186,12 +787,21 @@ SND_PCM_PLUGIN_DEFINE_FUNC(aaf)
snd_pcm_aaf_t *aaf;
int res;
+ /* For now the plugin only supports Playback mode i.e. AAF Talker
+ * functionality.
+ */
+ if (stream != SND_PCM_STREAM_PLAYBACK)
+ return -EINVAL;
+
aaf = calloc(1, sizeof(*aaf));
if (!aaf) {
SNDERR("Failed to allocate memory");
return -ENOMEM;
}
+ aaf->sk_fd = -1;
+ aaf->timer_fd = -1;
+
res = aaf_load_config(aaf, conf);
if (res < 0)
goto err;
@@ -200,6 +810,7 @@ SND_PCM_PLUGIN_DEFINE_FUNC(aaf)
aaf->io.name = "AVTP Audio Format (AAF) Plugin";
aaf->io.callback = &aaf_callback;
aaf->io.private_data = aaf;
+ aaf->io.flags = SND_PCM_IOPLUG_FLAG_BOUNDARY_WA;
res = snd_pcm_ioplug_create(&aaf->io, name, stream, mode);
if (res < 0) {
SNDERR("Failed to create ioplug instance");
diff --git a/doc/aaf.txt b/doc/aaf.txt
index 24ea888..b1a3f43 100644
--- a/doc/aaf.txt
+++ b/doc/aaf.txt
@@ -9,6 +9,46 @@ to transmit/receive audio samples through a Time-Sensitive Network (TSN)
capable network. The plugin enables media applications to easily implement AVTP
Talker and Listener functionalities.
+AVTP is designed to take advantage of generalized Precision Time Protocol
+(gPTP) and Forwarding and Queuing Enhancements for Time-Sensitive Streams
+(FQTSS).
+
+gPTP ensures AVTP talkers and listeners share the same time reference so the
+presentation time from AVTP can be used to inform when PCM samples should be
+presented to the application layer. Thus, in order to work properly, the plugin
+requires the system clock is synchronized with the PTP time. Such functionality
+is provided by ptp4l and phc2sys from Linuxptp project
+(linuxptp.sourceforge.net). ptp4l and phc2sys can be set up in many different
+ways, below we provide an example. For further information check ptp4l(8) and
+phc2sys(8).
+
+On PTP master host run the following commands. Replace $IFNAME by your PTP
+capable NIC name. The gPTP.cfg file mentioned below can be found in
+/usr/share/doc/linuxptp/ (depending on your distro).
+ $ ptp4l -f gPTP.cfg -i $IFNAME
+ $ phc2sys -f gPTP.cfg -c $IFNAME -s CLOCK_REALTIME -w
+
+On PTP slave host run:
+ $ ptp4l -f gPTP.cfg -i $IFNAME -s
+ $ phc2sys -f gPTP.cfg -a -r
+
+FQTSS provides bandwidth reservation and traffic prioritization for the AVTP
+stream. Thus, in order to work properly, the plugin requires FQTSS to be
+configured properly. The FQTSS features is supported by Linux Traffic Control
+system through the mpqrio and cbs qdiscs. Below we provide an example to
+configure those qdiscs in order to transmit an AAF stream with 48 kHz sampling
+rate, 16-bit sample size, stereo. For further information on how to configure
+it check tc-mqprio(8) and tc-cbs(8) man pages.
+
+Configure mpqrio (replace $HANDLE_ID by an unused handle ID):
+ $ tc qdisc add dev $IFNAME parent root handle $HANDLE_ID mqprio \
+ num_tc 3 map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \
+ queues 1 at 0 1 at 1 2 at 2 hw 0
+
+Configure cbs:
+ $ tc qdisc replace dev $IFNAME parent $HANDLE_ID:1 cbs idleslope 5760 \
+ sendslope -994240 hicredit 9 locredit -89 offload 1
+
Dependency
----------
--
2.14.4
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