ALSA: firewire-tascam: perform sequence replay for media clock recovery
authorTakashi Sakamoto <o-takashi@sakamocchi.jp>
Mon, 31 May 2021 02:51:02 +0000 (11:51 +0900)
committerTakashi Iwai <tiwai@suse.de>
Tue, 1 Jun 2021 06:19:37 +0000 (08:19 +0200)
commita9dd8a61b6b1fdf334d0cc63672b3ffac3827f18
tree23f18200c29b3856108e6afe74bd97515323eab6
parent019af5923c8a46b581fc2f2d670dcc0714a80bf0
ALSA: firewire-tascam: perform sequence replay for media clock recovery

This commit takes ALSA firewire-tascam driver to perform sequence replay
for media clock recovery.

The protocol specific to Tascam FireWire series is not compliant to
IEC 61883-1/6 in terms of syt field of CIP. The protocol doesn't use
presentation time in received CIP for playback timing. The sequence of
the number of data blocks per packet is important for media clock
recovery.

Although the devices in Tascam FireWire series transfer packets
regardless of receiving packets, the tx packets includes no events
in the beginning of streaming. It takes so long to multiplex any event
into the packet after receiving the sequence of packets. As long as I
experienced, it takes several thousands of isochronous cycle. Furthermore,
just after changing sampling transmission frequency, it stops multiplexing
event at once, then starts multiplexing again.

The sequence replay is tested with below models:
 * FW-1884
 * FW-1804
 * FW-1082

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20210531025103.17880-6-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Iwai <tiwai@suse.de>
sound/firewire/tascam/tascam-stream.c
sound/firewire/tascam/tascam.h