From mboxrd@z Thu Jan  1 00:00:00 1970
From: Henrik Austad <henrik@austad.us>
Subject: Re: [very-RFC 0/8] TSN driver for the kernel
Date: Sun, 12 Jun 2016 10:31:22 +0200
Message-ID: <20160612083122.GB32724@icarus.home.austad.us>
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To: Takashi Sakamoto <o-takashi@sakamocchi.jp>
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On Sun, Jun 12, 2016 at 01:30:24PM +0900, Takashi Sakamoto wrote:
> On Jun 12 2016 12:38, Takashi Sakamoto wrote:
> > In your patcset, there's no actual codes about how to handle any
> > interrupt contexts (software / hardware), how to handle packet payload,
> > and so on. Especially, for recent sound subsystem, the timing of
> > generating interrupts and which context does what works are important to
> > reduce playback/capture latency and power consumption.
> >=20
> > Of source, your intention of this patchset is to show your early concept
> > of TSN feature. Nevertheless, both of explaination and codes are
> > important to the other developers who have little knowledges about TSN,
> > AVB and AES-64 such as me.
>=20
> Oops. Your 5th patch was skipped by alsa-project.org. I guess that size
> of the patch is too large to the list service. I can see it:
> http://marc.info/?l=3Dlinux-netdev&m=3D146568672728661&w=3D2
>=20
> As long as seeing the patch, packets are queueing in hrtimer callbacks
> every 1 seconds.

Actually, the hrtimer fires every 1ms, and that part is something I have to=
=20
do something about, also because it sends of the same number of frames=20
every time, regardless of how accurate the internal timer is to the rest of=
=20
the network (there's no backpressure from the networking layer).

> (This is a high level discussion and it's OK to ignore it for the
> moment. When writing packet-oriented drivers for sound subsystem, you
> need to pay special attention to accuracy of the number of PCM frames
> transferred currently, and granularity of the number of PCM frames
> transferred by one operation. In this case, snd_avb_hw,
> snd_avb_pcm_pointer(), tsn_buffer_write_net() and tsn_buffer_read_net()
> are involved in this discussion. You can see ALSA developers' struggle
> in USB audio device class drivers and (of cource) IEC 61883-1/6 drivers.)

Ah, good point. Any particular parts of the USB-subsystem I should start=20
looking at? Knowing where to start looking is a tremendous help

Thanks for the feedback!

--=20
Henrik Austad

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