IRIG106wiki

IEEE 1394 Data, Format 0 packets are used to record data messages at the transaction layer of the IEEE 1394 serial data bus. Currently IEEE 1394, IEEE 1995, IEEE 1394a, and IEEE 1394b are supported. There are two major classes of IEEE 1394 data transfer, synchronous and isochronous. Synchronous data transfer is used to transport real time data streams such as video. Isochronous transfer is used to transport other non-time critical data on a best effort basis without latency or throughput guarantees.

At the lowest network level, IEEE 1394 defines three types of bus packets; a PHY packet, a Primary packet, and an Acknowledgement packet. There are several different types of Primary packets. Primary packets contain a Transaction Code to distinguish them. There are three different types of IEEE 1394 Data, Format 0 packets. The Chapter 10 standard refers to these as Type 0, Type 1, and Type 2. Type 0 packets are used to record bus events such as Bus Reset. Type 1 packets are used to record synchronous streams only (Primary packets with a TCODE of 0x0A). Type 2 packets are for more general purpose use and are used to record all 1394 packets including PHY, Primary, and Ack packets.

The layout of the CSDW is shown in Figure 6-47. The uPacketType value indicates the packet body type. The uSyncCode value is the value of the 1394 Synchronization Code between transaction packets. The IEEE 1394 standard describes the Synchronization Code as “an application-specific control field”, and “a synchronization point may be the defined as boundary between video or audio frames, or any other point in the data stream the application may consider appropriate.” The uTransCnt value is the number of separate transaction messages in the data packet.

struct Su1394F0_ChanSpec 
    { 
    uint32_t    uTransCnt   : 16;   // Transaction count 
    uint32_t    Reserved    :  9; 
    uint32_t    uSyncCode   :  4;   // Synchronization code 
    uint32_t    uPacketType :  3;   // Packet body type 
    }; 

Type 0 and Type 1 data packets will not have an intra-packet header. Type 2 data packets will have intra-packet headers between transaction data messages with the data packet. The Type 2 intra-packet header is an 8 byte time value. Time is represented in either 48-bit relative time format derived from the RTC (format shown in Figure 6-5), or as absolute time. If this time is absolute time, it is in either Chapter 4 weighted 48-bit time (format shown in Figure 6-6) or IEEE 1588 time format (format shown in Figure 6-7).

The IEEE 1394 standards contain quite a bit of example code and data structures in the C language to aid in data interpretation.

Chapter 10 of IRIG 106-07 (and prior editions of the standard) incorrectly state that Bit 7 of the Packet Flags (in the packet header) is used to determine if the intra-packet time is relative time or absolute time. The correct bit to use is Bit 6. This handbook is based on (and correlates to) the IRIG 106-07 edition; however the “bit 7” error will be corrected in future releases of this handbook.

IEEE 1394 Data, Format 1 packets are used to record IEEE 1394 at the physical layer. All bus data and bus events can be recorded in Format 1 packets. The IEEE 1394 Data, Format 0, Type 2 data packet provides a similar capability for capturing all bus traffic at the physical level. This Format 1 packet provides more status information, though, and is preferred over the Format 0, Type 2 data packet.

The layout of the CSDW is shown in Figure 6-48. The uPacketCnt value indicates the number of separate 1394 data messages in the data packet.

struct Su1394F1_ChanSpec 
    { 
    uint32_t    uPacketCnt  : 16;   // Number of messages 
    uint32_t    Reserved    : 16; 
    }; 

Individual 1394 data messages follow the CSDW. The format of the intra-packet data header is shown in Figure 6-49. The suIntrPckTime value is an eight byte representation of time in either 48-bit relative time format derived from the RTC (format shown in Figure 6-5) , or as absolute time. If this time is absolute time, it is in either Chapter 4 weighted 48-bit time (format shown in Figure 6-6) or IEEE 1588 time format (format shown in Figure 6-7). The uDataLength field is the length of the 1394 data message in bytes. The bLBO flag indicates that some 1394 packets were lost by the bus monitor due to an overflow in the local message buffer. The uTrfOvf value indicates a 1394 transfer protocol error. The uStatus field indicates the value of the eight-bit Bus Status Transfer from the PHY to the link layer of the 1394 bus. Bus Status Transfers are used to signal:

a. A Bus Reset indication.
b. An Arbitration Reset Gap indication (both even and odd).
c. A Subaction Gap indication.
d. A Cycle Start indication (both even and odd).

See IEEE 1394b-2002 Section 17.8 for more details about interpreting uStatus.

struct SuIEEE1394F1_Header 
    { 
    uint64_t    suIntraPckTime;         // Reference time 
    uint32_t    uDataLength     : 16;   // Data length 
    uint32_t    Reserved        : 1;    // 
    uint32_t    bLBO            : 1;    // Local buffer overflow 
    uint32_t    uTrfOvf         : 2;    // Transfer overflow 
    uint32_t    uSpeed          : 4;    // Transmission speed 
    uint32_t    uStatus         : 8;    // Status byte 
    }; 

The complete 1394 bus data message follows the intra-packet data header. The length of the 1394 data message is indicated in the intra-packet data header. If the data length is not a multiple of four, the data buffer will contain padding bytes to align the buffer on a four byte boundary. The IEEE 1394 standards contain quite a bit of example code and data structures in the C language to aid in data interpretation.

Reserved for future use.