The avionics buses ARINC 429 and high speed MIL-STD-1553 have been joined by commercial standards such as Ethernet, CAN bus and FireWire. Curtiss-Wright provides parsers, snarfers and packetizers to monitor a wide range of buses in a standardized manner without interfering with the buses’ operation.
- Parser – Extracts specific data from a bus and places it into defined words along with status information. Data is triple buffered to ensure the data remains coherent. A MIL-STD-1553 parser is sometimes referred to as an IRIG-106 Chapter 4 monitor.
- Snarfer – Places traffic and tags, along with content identifiers, into a FIFO that ensures data is not lost if read fast enough. For MIL-STD-1553, snarfing is sometimes referred to as Chapter 8 or All-bus monitoring.
- Packetizer – Coherently embeds multiple whole messages/frames/packets of various lengths in an IP packet. Because traffic and tags can be inferred from the location in the packet payload, content identifiers are not required and therefore less overhead/bandwidth is required. There are also overhead savings with respect to time and status information which can be IP packet wide.
The KAD/ABM/103, a 24-channel ARINC-429 bus monitor, is one example of a Curtiss-Wright avionic bus monitor that features the functions of a coherent message parser with the flexibility of an iNET-X packetizer. Other capabilities include message counting and extensive error detection functions.
Through aperiodic packet transmission, the system prevents loss of messages. What makes this possible is the Acra KAM-500 controller, which oversamples and generates packets for transmission only when the buffer is not empty – when at least one new message has been captured from the bus.