Re: [linux-minidisc] netmd command to retrieve the date and time of a recording

[Michael Karcher <Michael.Karcher@fu-berlin.de>]

Am Mittwoch, den 28.04.2010, 17:50 +0200 schrieb Jan Olav Stangeland:
> Thank you,
> 
> as reference I was speculating that perhaps proper values for p1, p2 would
> do the trick:
> 
> def _getTrackInfo(self, track, p1, p2):
>  query = self.formatQuery('1806 02201001 %w %w %w ff00 00000000', track,
>                           p1, p2)
>  reply = self.send_query(query)
>  return self.scanQuery(reply, '1806 02201001 %?%? %?%? %?%? 1000 ' \
>                        '00%?0000 %x')[0]

So, "content_creation_date_and_time" has the information block ID 4,
according to TA2000004 ("Enhancements to the AV/C General Specification
3.0 Version 1.1"). The command you quote is (06) a READ INFO BLOCK
command, described in TA1999035 ("AV/C Descriptor Mechanism
Specification Version 1.0"). The 02 means the info block path has two
elements. The 20 means that an indexed subentry of some directory is to
be used. The 1001 is (according to TA1998014 ("AV/C Disc Media Type
Specification - MD audio")) the directory of audio tracks, which is
followed by a 16 bit word for the track number. p1 and p2 is a quite
illogic separation of the following bytes, which is a result of not
understanding the base protocol.

Reading info about a track always starts with
06 - READ DESCRIPTOR 
  02 - TWO LEVELS
     20 1001 <trknum> - 1st Level: the chosen track in the trakc list
     30 <infoblkid> 00 - 2nd Level: 1st occurrence of info block with id

So for the track creation time, you have p1 == 0x3000 and p2 == 0x0400.
The format of the time stamp is
 1st byte: bit 7 - set if valid
           bit 6 - set if the timestamp is an abstract count,
                   clear if an absolute time
           bit 5-0: high bits of year
 2nd byte: low bits of year
 3rd byte: month
 4th byte: day
 5th byte: hours
 6th byte: minutes
 7th byte: seconds

If the timestamp is an abstract count, all bits specified for the
timestamp (with most significant bits in 1st byte and last significant
bits in 7th byte) form a 54 bit count which is incremented once on each
"event". What kind of "events" are counted is device specific, but MD
should only use absolute time anyway.

Regards,
  Michael Karcher

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