1394 time stamp

Akh_Ind · 18th November 2003, 09:25 AM

How to insert a time stamp on a Isochronous A/V packet which is to be transmitted on 1394 bus.

dr1394 · 23rd November 2003, 10:21 AM

The 1394 timestamp is used to convey a clock
(other than the 24.576 1394 clock itself) to
the receiver. For DV, the timestamp conveys
the video frame rate. For MPEG-2 the timestamp
conveys the system 27 MHz clock. For 1394 audio
(A&M protocol), the timestamp conveys the audio
sample clock.

Since this is generally an audio website, I'll
assume you're interested in A&M protocol. DV
and MPEG-2 timestamps are the same concept, but
the details are a bit different.

Here's a bus analyzer trace of a few A&M audio
packets. This is 44.1/16 PCM from the Pioneer
DV-47Ai. 44.1/16 is sent without encryption,
so the audio samples can be seen.

Code:

          TCODE OR       QUADDATA
 STORE#  EVENT TYPE  SPD MSB  LSB CNT        DESCRIPTION FIELD        TIMESTAMP
 000000 CYCLE_START  100 FFFF008F  01 DEST=3FF:3F  TL=00  RT=0  PRI=F  0.000 US
 000001 ASYNC        100 FFC3FFFF  02 SRC= 3FF:03                      0.330 US
 000002 ASYNC        100 F0000200  03 DEST_OFFST=CSR: CYCLE_TIME       0.320 US
 000003 ASYNC        100 F2650024  04 CYCLE TIME                       0.330 US
 000004 ASYNC        100 BF764C16  05 HEADER CRC                       0.320 US
 000005 ISO_DATABLK  100 00487FA2  01 LENGTH=0048  CHNL=7F  SYNC=2     1.100 US
 000006 ISO          100 748BF64D  02 HEADER CRC                       0.330 US
 000007 ISO          100 03020060  03                                  0.320 US
 000008 ISO          100 900122BE  04 SYT = 0x22be                     0.330 US
 000009 ISO          100 18E20E00  05                                  0.320 US
 000010 ISO          100 00E5B600  06                                  0.330 US
 000011 ISO          100 18DCB700  07                                  0.320 US
 000012 ISO          100 00E1CF00  08                                  0.330 US
 000013 ISO          100 10D70000  09                                  0.330 US
 000014 ISO          100 02DB4900  10                                  0.320 US
 000015 ISO          100 1AD38300  11                                  0.330 US
 000016 ISO          100 08D87A00  12                                  0.320 US
 000017 ISO          100 10D07300  13                                  0.330 US
 000018 ISO          100 08D80700  14                                  0.320 US
 000019 ISO          100 18CA4600  15                                  0.330 US
 000020 ISO          100 00D59400  16                                  0.320 US
 000021 ISO          100 18C37000  17                                  0.330 US
 000022 ISO          100 00D36700  18                                  0.330 US
 000023 ISO          100 10C04700  19                                  0.320 US
 000024 ISO          100 08D4E600  20                                  0.330 US
 000025 ISO          100 8347D14E  21                                  0.320 US
 000026 SUBACTN GAP  100                                               10.83 US
 000027 ARB GAP      100                                               10.49 US
 000028 CYCLE_START  100 FFFF008F  01 DEST=3FF:3F  TL=00  RT=0  PRI=F  94.77 US
 000029 ASYNC        100 FFC3FFFF  02 SRC= 3FF:03                      0.330 US
 000030 ASYNC        100 F0000200  03 DEST_OFFST=CSR: CYCLE_TIME       0.320 US
 000031 ASYNC        100 F2651024  04 CYCLE TIME                       0.330 US
 000032 ASYNC        100 AF27D705  05 HEADER CRC                       0.320 US
 000033 ISO_DATABLK  100 00487FA2  01 LENGTH=0048  CHNL=7F  SYNC=2     1.100 US
 000034 ISO          100 748BF64D  02 HEADER CRC                       0.330 US
 000035 ISO          100 03020068  03                                  0.320 US
 000036 ISO          100 90013828  04 SYT = 0x3828                     0.330 US
 000037 ISO          100 18C13A00  05                                  0.320 US
 000038 ISO          100 02DB0800  06                                  0.330 US
 000039 ISO          100 12C4B100  07                                  0.320 US
 000040 ISO          100 00DF7F00  08                                  0.330 US
 000041 ISO          100 10C5CA00  09                                  0.330 US
 000042 ISO          100 08E19700  10                                  0.320 US
 000043 ISO          100 18CA9D00  11                                  0.330 US
 000044 ISO          100 00E6BA00  12                                  0.320 US
 000045 ISO          100 10D23F00  13                                  0.330 US
 000046 ISO          100 08EA2D00  14                                  0.320 US
 000047 ISO          100 10D77D00  15                                  0.330 US
 000048 ISO          100 08EA8400  16                                  0.320 US
 000049 ISO          100 30D7B400  17                                  0.330 US
 000050 ISO          100 0AE9EA00  18                                  0.330 US
 000051 ISO          100 12D6B400  19                                  0.320 US
 000052 ISO          100 08EAA500  20                                  0.330 US
 000053 ISO          100 8234C6F4  21                                  0.320 US
 000054 SUBACTN GAP  100                                               10.83 US
 000055 ARB GAP      100                                               10.49 US
 000056 CYCLE_START  100 FFFF008F  01 DEST=3FF:3F  TL=00  RT=0  PRI=F  94.77 US
 000057 ASYNC        100 FFC3FFFF  02 SRC= 3FF:03                      0.320 US
 000058 ASYNC        100 F0000200  03 DEST_OFFST=CSR: CYCLE_TIME       0.330 US
 000059 ASYNC        100 F2652024  04 CYCLE TIME                       0.330 US
 000060 ASYNC        100 9FD57A30  05 HEADER CRC                       0.320 US
 000061 ISO_DATABLK  100 00087FA2  01 LENGTH=0008  CHNL=7F  SYNC=2     1.100 US
 000062 ISO          100 02A0D78D  02 HEADER CRC                       0.330 US
 000063 ISO          100 03020070  03                                  0.320 US
 000064 ISO          100 9001FFFF  04                                  0.330 US
 000065 ISO          100 CDA82563  05                                  0.320 US
 000066 SUBACTN GAP  100                                               10.83 US
 000067 ARB GAP      100                                               10.49 US
 000068 CYCLE_START  100 FFFF008F  01 DEST=3FF:3F  TL=00  RT=0  PRI=F  99.98 US
 000069 ASYNC        100 FFC3FFFF  02 SRC= 3FF:03                      0.330 US
 000070 ASYNC        100 F0000200  03 DEST_OFFST=CSR: CYCLE_TIME       0.320 US
 000071 ASYNC        100 F2653024  04 CYCLE TIME                       0.330 US
 000072 ASYNC        100 8F84E123  05 HEADER CRC                       0.320 US
 000073 ISO_DATABLK  100 00487FA2  01 LENGTH=0048  CHNL=7F  SYNC=2     1.100 US
 000074 ISO          100 748BF64D  02 HEADER CRC                       0.330 US
 000075 ISO          100 03020070  03                                  0.320 US
 000076 ISO          100 90015192  04                                  0.330 US
 000077 ISO          100 10DA5D00  05                                  0.320 US
 000078 ISO          100 08EB6D00  06                                  0.330 US
 000079 ISO          100 18DA1700  07                                  0.330 US
 000080 ISO          100 00EBBB00  08                                  0.320 US
 000081 ISO          100 10D48B00  09                                  0.330 US
 000082 ISO          100 08ED9200  10                                  0.320 US
 000083 ISO          100 10D05700  11                                  0.330 US
 000084 ISO          100 00EE2E00  12                                  0.320 US
 000085 ISO          100 18D13200  13                                  0.330 US
 000086 ISO          100 0AEF8C00  14                                  0.320 US
 000087 ISO          100 10D09700  15                                  0.330 US
 000088 ISO          100 00EF1F00  16                                  0.320 US
 000089 ISO          100 14C9DC00  17                                  0.330 US
 000090 ISO          100 0CEAE600  18                                  0.330 US
 000091 ISO          100 10C7D900  19                                  0.320 US
 000092 ISO          100 08EA7800  20                                  0.330 US
 000093 ISO          100 6D51EAD2  21                                  0.320 US
 000094 SUBACTN GAP  100                                               10.83 US
 000095 ARB GAP      100                                               10.49 US

The first timestamp is 0x22be and the second
timestamp is 0x3828. 0x3828 - 0x22be = 0x156a.
However, the 1394 timestamp is really a bit
field composed of 12 bits 24.576 MHz ticks
modulo 3072, 13 bits of cycles modulo 8000 and
7 bits of seconds. So 0x156a is really 1386 +
3072 = 4458.

So there are 4458 24.576 MHz clock ticks between
the first sample of packet 1 and the first sample
of packet 2. 1/24576000 * 4458 = 181.396 microsec.

The number of samples in each packet is 8, so
the interval between 8 samples at 44100 Hz is
1/44100 * 8 = 181.405 microseconds.

That's the basic idea. Of course there's way
more implementation detail (like the empty packet
sent after the first two packets), but if you're
interested, I'll explain that in subsequent posts.

Ron

Akh_Ind · 24th November 2003, 04:14 AM

Hi,
Thanks a lot for your comprehensive answer.
But one thing which I am still unclear about is
how to extract a sampling clock frequency from
the received audio packet. (Packet sent on the
1394 bus has a time stamp on it. How do I extract
the sampling clock freq. using this time stamp ?)
Thanks again.

dr1394 · 24th November 2003, 01:08 PM

A way is needed to relate the 24.576 MHz 1394
clock (which by default is the same at all
nodes) to your local audio sampling clock. The
easiest way to do this is to have the value
of the 1394 clock latched at some interval by
the local audio clock. This is not a feature
you'll see on any general purpose 1394 LLC,
but keep reading. The TI TSB43CB43A has some
kind of clock recovery support, but I'm not
sure exactly how it works.

http://focus.ti.com/docs/prod/folder...sb43ca43a.html

Now it's know how many 1394 clocks are in x amount
of local audio samples. In my post example, the
1394 timestamps are telling us that there are
4458 1394 clocks for every 8 samples. If the
1394 clock value is latched every 8 samples with
the local audio clock, the difference between
successive latched 1394 clock values will be
somewhere around 4458.

By using a VCXO for the local audio clock, the CPU
can change the frequency (measured in 1394 clocks)
to match the timestamps. It's a "software PLL"
so to speak. A low-pass filter on the timestamp
values is required to eliminate the large
inherent jitter (1/24576000 = 40 nanosecond,
which is a lot).

Here's a very well written paper on 1394 clock
recovery jitter:

http://www.nanophon.com/audio/1394_sampling_jitter.pdf

In that paper, one of the solutions offered is
in section 8.4.5 and is what is being used by
the current 1394 implementations by Pioneer,
Sony, Denon and Yamaha. Instead of the receiver
trying to recover the sampling clock, the
receiver controls the rate of transmission from
the source with a rate control protocol sent over
the very same 1394 bus. The receiver use a fixed
rate sample clock (which can be a high quality,
low-jitter crystal oscillator) and just monitors
the level of it's receive packet buffer. If an
upper threshold is hit, the receiver sends a
"SLOW" rate control request to the source.
Likewise, if a lower threshold is hit, the
receiver sends a "FAST" rate control request.
Since the rate of change in the buffer level
is quite slow (that is, the phase of the player
and receiver clocks are not that far off to begin
with), this scheme works fantastically well.

The manufacturers all have their own name for
this protocol. Pioneer calls it PQLS, Sony calls
it HATS and Denon has yet another name. The
real specification is called "AV/C Command Set
for Rate Control of Isochronous Data Flow 1.0"
which is an open specification available from
the 1394 Trade Association:

http://1394ta.org

Unfortunately, the specifications can be
downloaded by 1394ta members only.

So the ultimate solution to the clock recovery
problem is to not do it.

Ron

18th November 2003, 09:25 AM	#1
Akh_Ind diyAudio Member Join Date: Nov 2003 Location: India	1394 time stamp How to insert a time stamp on a Isochronous A/V packet which is to be transmitted on 1394 bus.

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24th November 2003, 04:14 AM	#3
Akh_Ind diyAudio Member Join Date: Nov 2003 Location: India	Hi, Thanks a lot for your comprehensive answer. But one thing which I am still unclear about is how to extract a sampling clock frequency from the received audio packet. (Packet sent on the 1394 bus has a time stamp on it. How do I extract the sampling clock freq. using this time stamp ?) Thanks again.

24th November 2003, 01:08 PM	#4
dr1394 diyAudio Member Join Date: Nov 2003 Location: Silicon Valley	A way is needed to relate the 24.576 MHz 1394 clock (which by default is the same at all nodes) to your local audio sampling clock. The easiest way to do this is to have the value of the 1394 clock latched at some interval by the local audio clock. This is not a feature you'll see on any general purpose 1394 LLC, but keep reading. The TI TSB43CB43A has some kind of clock recovery support, but I'm not sure exactly how it works. http://focus.ti.com/docs/prod/folder...sb43ca43a.html Now it's know how many 1394 clocks are in x amount of local audio samples. In my post example, the 1394 timestamps are telling us that there are 4458 1394 clocks for every 8 samples. If the 1394 clock value is latched every 8 samples with the local audio clock, the difference between successive latched 1394 clock values will be somewhere around 4458. By using a VCXO for the local audio clock, the CPU can change the frequency (measured in 1394 clocks) to match the timestamps. It's a "software PLL" so to speak. A low-pass filter on the timestamp values is required to eliminate the large inherent jitter (1/24576000 = 40 nanosecond, which is a lot). Here's a very well written paper on 1394 clock recovery jitter: http://www.nanophon.com/audio/1394_sampling_jitter.pdf In that paper, one of the solutions offered is in section 8.4.5 and is what is being used by the current 1394 implementations by Pioneer, Sony, Denon and Yamaha. Instead of the receiver trying to recover the sampling clock, the receiver controls the rate of transmission from the source with a rate control protocol sent over the very same 1394 bus. The receiver use a fixed rate sample clock (which can be a high quality, low-jitter crystal oscillator) and just monitors the level of it's receive packet buffer. If an upper threshold is hit, the receiver sends a "SLOW" rate control request to the source. Likewise, if a lower threshold is hit, the receiver sends a "FAST" rate control request. Since the rate of change in the buffer level is quite slow (that is, the phase of the player and receiver clocks are not that far off to begin with), this scheme works fantastically well. The manufacturers all have their own name for this protocol. Pioneer calls it PQLS, Sony calls it HATS and Denon has yet another name. The real specification is called "AV/C Command Set for Rate Control of Isochronous Data Flow 1.0" which is an open specification available from the 1394 Trade Association: http://1394ta.org Unfortunately, the specifications can be downloaded by 1394ta members only. So the ultimate solution to the clock recovery problem is to not do it. Ron

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