4641c93940
MOTU FireWire series uses blocking transmission for AMDTP packet streaming. They transmit/receive 8,000 packets per second, to handle the same number of data blocks as current sampling transmission frequency. Thus, IEC 61883-1/6 packet streaming engine of ALSA firewire stack is available for them. However, the sequence of packet and data blocks includes some quirks. Below sample is a sequence of CIP headers of packets received by 828mk2, at 44.1kHz of sampling transmission frequency. quads CIP1 CIP2 488 0x020F04E8 0x8222FFFF 8 0x020F04F8 0x8222FFFF 488 0x020F0400 0x8222FFFF 488 0x020F0408 0x8222FFFF 8 0x020F04E8 0x8222FFFF 488 0x020F04F0 0x8222FFFF 488 0x020F04F8 0x8222FFFF The SID (source node ID), DBS (data block size), SPH (source packet header), FMT (format ID), FDF (format dependent field) and SYT (time stamp) fields are in IEC 61883-1. Especially, FMT is 0x02, FDF is 0x22 and SYT is 0xffff to define MOTU specific protocol. In an aspect of dbc field, the value represents accumulated number of data blocks included the packet. This is against IEC 61883-1, because according to the specification this value should be the number of data blocks already transferred. In ALSA IEC 61883-1/6 engine, this quirk is already supported by CIP_DBC_IS_END_EVENT flag, because Echo Audio Fireworks has. Each data block includes SPH as its first quadlet field, to represent its presentation time stamp. Actual value of SPH is compliant to IEC 61883-1; lower 25 bits of 32 bits width consists of 13 bits cycle count and 12 bits cycle offset. The rest of each data block consists of 24 bit chunks. All of PCM samples, MIDI messages, status and control messages are transferred by the chunks. This is similar to '24-bit * 4 Audio Pack' in IEC 61883-6. The position of each kind of data depends on generations of each model. The number of whole chunks in a data block is a multiple of 4, to consists of quadlet-aligned packets. This commit adds data block processing layer specific for the MOTU protocol. The remarkable point is the way to generate SPH header. Time stamps for each data blocks are generated by below calculation: * Using pre-computed table for the number of ticks per event * 44,1kHz: (557 + 123/441) * 48.0kHz: (512 + 0/441) * 88.2kHz: (278 + 282/441) * 96.0kHz: (256 + 0/441) * 176.4kHz: (139 + 141/441) * 192.0kHz: (128 + 0/441) * Accumulate the ticks and set the value to SPH for every events. * This way makes sense only for blocking transmission because this mode transfers fixed number or none of events. This calculation assumes that each data block has a PCM frame which is sampled according to event timing clock. Current packet streaming layer has the same assumption. Although this sequence works fine for MOTU FireWire series at sampling transmission frequency based on 48.0kHz, it is not enough at the frequency based on 44.1kHz. The units generate choppy noise every few seconds. Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp> Signed-off-by: Takashi Iwai <tiwai@suse.de> |
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| firmware | ||
| fs | ||
| include | ||
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| ipc | ||
| kernel | ||
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| security | ||
| sound | ||
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| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.