CHAPTER 10

DIGITAL ON-BOARD RECORDER STANDARD

2005

10.6 Data Format Definition

10.6.3 Time Data Packets.

10.6.3.1 Time Data Packets, Format 0.

Reserved.

10.6.3.2 Time Data Packets, Format 1.

Time is treated like another data channel. If a time source other than "none" is used, the time packet will be generated at a minimum rate of 1000 milliseconds.

  1. IRIG Time Type Formats. The 48-bit relative time counter shall be captured for insertion into the Time Packet Data header IAW IRIG 200 Serial Time Code Formats; On-Time Reference Marker definition.
  2. All Non-IRIG Time Type Formats. The 48-bit relative time counter shall be captured for insertion into the Time Packet Data header at an integer multiple of 10 milliseconds.

    A Time Data Packet shall be the first dynamic data packet at the start of each recording. Only static Computer Generated Data packets may precede the Time Data Packet in the recording.

    If the Time Data Packet Source is None at least one Time Data Packet is required IAW the previous note.

    A packet with time data has the basic structure shown in Figure 10-15. Note that the width of the structure is not related to any number of bits. This drawing is merely to represent relative placement of data in the packet. Time Packets do not have Intra-Packet Headers.

    PACKET HEADER
    CHANNEL SPECIFIC DATA
    TIME DATA
    PACKET TRAILER
    Figure 10-15. General time data packet, format 1.

    Time Packet Channel Specific Data. The Packet Body portion of each Time Data Packet begins with a Channel Specific Data word formatted as shown in Figure 10-16a

    msb
    31
    12 11 8 7 4 3 lsb
    0
    RESERVED
    DATE
    FMT
    SRC
    • Time Source (SRC). (bits 3-0) indicates the source of the time in the payload of each time packet.

      0x0 = Internal (Time derived from the Clock in the Recorder)
      0x1 = External (Time derived from a Clock not in the Recorder)
      0x2 = Internal from RMM (Internal Time derived from the Clock in the RMM)
      0x3 - 0xE = Reserved
      0xF = None
    • Time Format (FMT). (bits 7-4) indicate the Time Data Packet format. All bit patterns not used to define a time format type are reserved for future data type growth.

      0x0 = IRIG-B
      0x1 = IRIG-A
      0x2 = IRIG-G
      0x3 = Internal Real-Time Clock
      0x4 = UTC Time from GPS
      0x5 = Native GPS Time
      0x6 thru 0xE = Reserved
      0xF = None (time packet payload invalid)
    • Date Format (DATE). (bits 11-8) indicate the Date format. All bit patterns not used to define a date format type are reserved for future growth.
      Bits 11-10:Reserved
      Bit 9:Indicates Date Format
      0 = IRIG day available
      1 = Month and Year available
      Bit 8:Indicates if this is a leap year
      0 = Not a leap year
      1 = Is a leap year
    • Reserved. (bits 31-12) are reserved.

    Figure 10-16a. Time packet channel specific data format.

  3. Time Packet Body. After the Channel Specific Data word, the time data words are inserted in the packet in Binary Coded Decimal (BCD) format as shown in Figure 10-16b and Figure 10-16c.

    msb
    15
    12 11 8 7 4 3 lsb
    0
    0 TSn Sn Hmn Tmn
    0 0 THn Hn 0 TMn Mn
    0 0 0 0 0 0 HDn TDn Dn

    Figure 10-16b. Time data - packet format, day format.

    msb
    15
    12 11 8 7 4 3 lsb
    0
    0 TSn Sn Hmn Tmn
    0 0 THn Hn 0 TMn Mn
    0 0 0 TOn On TDn Dn
    0 0 OYn HYn TYn Yn

    Figure 10-16c. Time data - packet format, day, month, and year format

    The following units of measure apply to Figure 10-16b and Figure 10-16c.

    TmnTens of milliseconds TDnTens of days
    HmnHundreds of milliseconds HDnHundreds of Days
    Sn Units of seconds On Units of Months
    TSnTens of Seconds TOnTens of Months
    Mn Units of minutes Yn Units of Years
    TMnTens of minutes TYnTens of Years
    Hn Units of hours HYnHundreds of Years
    THnTens of Hours OYnThousands of Years
    Dn Units of Days 0 Always zero
add a note add a comment User Contributed Notes and Comments

Deprecated: Function strftime() is deprecated in /web/irig106/comments/show.inc on line 89
01/15/2007 23:11 - Bob (bob dot baggerman at gatech dot edu)
A note says "A Time Data Packet shall be the first dynamic data packet". I'm not sure exactly what constitutes a "Dynamic Data" packet. It would be nice if this were more specific.

Deprecated: Function strftime() is deprecated in /web/irig106/comments/show.inc on line 89
01/15/2007 23:08 - Bob (bob dot baggerman at gatech dot edu)
The spec doesn't explicitly specify when either time format from Figure 10-16b or Figure 10-16c. Format seems to come "Date format" but the wording isn't very specific. It would be clearer if the spec said "Bit 9, 0 = Use Figure 10-16b, 1 = Use Figure 10-16c.

Also, the bit fields for the Channel Specific Data are described from LSB to MSB, but Date Format description presents them MSB first. This turn around messed me up the first time I implemented time packets. It would be better if Date Format started with Bit 8.

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