[alsa-devel] DSD over HDMI: audio data packetization

[Anssi Hannula]

06.01.2015, 08:15, Andrej Falout kirjoitti:
> Hi Anssi,

Hi,

>> I think the One-Bit Audio and DST formats are just misnamed here and
>> can't be carried over IEC 61937 (ATRAC can be) - the IEC 61937
>> specification does not cover One-Bit Audio or DST.
>>
> 
> Does it have to be? Given that it is defined in CEA 861, and that 61937-1
> makes specific provisions for non-PCM data:
> 
> Page 16:
> 
> "In cases where the interface is used to convey non-linear PCM audio
> bitstreams..."

IEC 61937 *is* about transmitting non-PCM data. The specification
specifies how to encapsulate AC-3, MPEG-x, DTS, ATRAC, WMA etc for
transmission over IEC 60958 link. It does not specify anything about
One-Bit Audio or DST (see e.g. "Table 2 - Data-types" in IEC 61937-2 for
a list of supported types of which you need to select one).

>>
>> I think the "third-party solution" refers to a driver implementing
>> support for a non-HDA-spec HW feature which allows One-Bit audio / DST /
>> raw packets to be transmitted (in a similar way "EPT" (Encoded Packet
>> Type field in Pin Widget Control 7.3.3.13) allows setting HBR or ASP
>> packet transmission).
>>
>>
> Why would an "HW feature" be required to "allows One-Bit audio / DST / raw
> packets to be transmitted"?
> 
> What would such "HW feature" do? What could it possibly do?

It would allow transmission of One Bit Audio Sample Packets (HDMI spec
1.3a 5.3.9) or DST Audio Packets (HDMI spec 5.3.10), which is not
possible with HW that simply implements HDA specification. The HDA
specification only supports transmission of Audio Sample Packets (HDMI
spec 5.3.4) and High-Bitrate Audio Stream Packets (HDMI spec 5.3.11),
selectable via the EPT field (HDA spec 7.3.3.13).
The packet header (which e.g. identifies the packet type) is generated
by HW on HDA cards.

Uncompressed PCM is transmitted using ASP packets.
IEC 61937 is transmitted using ASP packets (<=6.144Mbps) or HBR packets
(>6.144Mbps).


> 
> Thanks,
> Andrej Falout
> 
> 
> 
> 
>>
>>> Thanks,
>>> Andrej Falout
>>>
>>> On Mon, Jan 5, 2015 at 4:46 PM, Anssi Hannula <anssi.hannula at iki.fi
>>> <mailto:anssi.hannula at iki.fi>> wrote:
>>>
>>>     04.01.2015, 05:10, Xuebing Wang kirjoitti:
>>>     > Anssi, Libin,
>>>     >
>>>     > Thanks for your help.
>>>     >
>>>     > After a little bit of research, I do think it is possible to
>> stream DSD
>>>     > over HDMI (the mechanism is as Anssi mentioned, similar way as
>> HBR).
>>>     >
>>>     > Please see HDA spec:
>>>     > 3.7.1 Stream Format Structure
>>>     > (If the TYPE is set to Non-PCM, the controller just pushes data
>> over the
>>>     > link and is not concerned
>>>     > with formatting. The base rate, data type, and number of Words
>> (MULT) to
>>>     > send each valid frame
>>>     > are specified to control the rate at which the non-PCM data is
>> sent.)
>>>     >
>>>     > 7.3.3.8 Converter Format
>>>     >
>>>     > What do you think? In order to implement this similiar mechanism
>>>     > (similar to HBR), I still have some detailed questions that I will
>> write
>>>     > in another email. Thanks.
>>>
>>>     That setting will still not allow you to send One-bit audio or DST
>>>     packets. The stream will still be encapsulated in either ASP or HBR
>>>     packets, depending on the value of the EPT field (Encoded Packet
>> Type,
>>>     7.3.3.13).
>>>
>>>
>>>     >
>>>     > On Thu, 2015-01-01 at 06:37 +0200, Anssi Hannula wrote:
>>>     >> 01.01.2015, 04:07, Yang, Libin kirjoitti:
>>>     >>> Hi,
>>>     >>>
>>>     >>>> -----Original Message-----
>>>     >>>> From: Anssi Hannula [mailto:anssi.hannula at iki.fi
>>>     <mailto:anssi.hannula at iki.fi>]
>>>     >>>> Sent: Wednesday, December 31, 2014 11:45 PM
>>>     >>>> To: Xuebing Wang
>>>     >>>> Cc: Yang, Libin; alsa-devel at alsa-project.org
>>>     <mailto:alsa-devel at alsa-project.org>; Lin, Mengdong; ; Takashi
>> Iwai; ;
>>>     >>>> Wu Fengguang
>>>     >>>> Subject: Re: [alsa-devel] DSD over HDMI: audio data
>> packetization
>>>     >>>>
>>>     >>>> 31.12.2014, 17:38, Xuebing Wang kirjoitti:
>>>     >>>>> Anssi, Libin,
>>>     >>>>>
>>>     >>>>> Thank you very much for your help.
>>>     >>>>>
>>>     >>>>> If L-PCM audio data packetization is done by hardware, is it
>>>     possible
>>>     >>>>> to implement DSD over HDMI on Intel integrated graphics?
>>>     Thanks again.
>>>     >>>>
>>>     >>>> I don't think so, unless:
>>>     >>>>
>>>     >>>> (a) It is possible to somehow encapsulate the stream in Audio
>>>     Sample
>>>     >>>> Packets and be accepted by the receiver (like e.g. AC3, DTS).
>>>     I'm not aware of
>>>     >>>> such a way.
>>>     >>>>
>>>     >>>> or:
>>>     >>>> (b) There is some undocumented feature in the Intel HDMI codecs
>>>     allowing
>>>     >>>> the driver to switch to DSD or driver-constructed packets
>>>     (instead of
>>>     >>>> ASP) in similar way as there is a way to switch to HBR packets.
>>>     >>>>
>>>     >>>
>>>     >>> Yes, I agree. And I'm not sure whether HDMI spec supports DSD.
>>>     >>
>>>     >> It does, via the "One Bit Audio" and "DST" formats (spec 5.3.9,
>>>     5.3.10
>>>     >> in 1.3a/1.4a).
>>>     >
>>>     >
>>>
>>>
>>>     --
>>>     Anssi Hannula
>>>
>>>
>>
>>
>> --
>> Anssi Hannula
>>
> 


-- 
Anssi Hannula