Hi all,
In this developing cycle for Linux 4.7, I concentrate on working to check packet sequence of ALSA firewire stack, because I ensure that the stack causes Dice-based models to generate sound including periodical noise or to generate no sound in the worst case. As of the end of developing cycle for Linux 4.6, I assumed that this is a bug of ALSA firewire stack[1]. However, the assumption is denied by my analysis with added tracepoints of Linux tracing framework[2]. Then, I concluded that the issue comes from quirks of Dice in an aspect of processing presentation timestamp.
I'm under further investigation and have seen some of the quirks. In this message, I describe the summary of superficial issues from the quirks, the status of ALSA firewire stack in Linux 4.6 for Dice-based models and direction of my work for ALSA firewire stack in this developing cycle.
Besides, resources and my memo for this work is available in this URL. I wish to upload it to alsa-project.org, not in my server: http://sakamocchi.jp/media/20160505-dice-packet-dump.tar.xz (233MB archive file compressed by xz, expands 6.7 GB text files.)
Summary - Dice ASICs/firmwares/drivers communicate with packet sequences which is partly not compliant to IEC 61883-6. - Dice ASICs/firmwares/drivers doesn't sometimes transfer data blocks as the same as sampling transfer frequency. - Calculation of presentation timestamp is not based on duration of data blocks in a packet. This way is different from implementation of ALSA firewire stack. - The value of estimated 'transfer delay' is against IEEE 1394 spec.
As a result: - ALSA dice driver causes these issues. ALSA dice driver in Linux kernels since 3.13 have included this issue. - To fix this issue, ALSA firewire stack require timestamp generator and data block calculator specific for Dice-based models. At least, three functions should be changed; amdtp_stream_start(), calculate_data_blocks(), calculate_syt() in 'sound/firewire/amdtp-stream.c'. - The work requires much changes, thus it's impossible for Linux 4.6. ALSA firewire stack in Linux 4.6 will be shipped with these issues. - We have a short time till merge window of Linux 4.7 (Just one week). I'll work for merging my proposed patchset[2][3][4], without fixing the issues.
[1] http://mailman.alsa-project.org/pipermail/alsa-devel/2016-March/105608.html [2] http://mailman.alsa-project.org/pipermail/alsa-devel/2016-April/106950.html [3] http://mailman.alsa-project.org/pipermail/alsa-devel/2016-April/107290.html [4] http://mailman.alsa-project.org/pipermail/alsa-devel/2016-April/107531.html
Regards
Takashi Sakamoto