What is byteflight?

The permanently increasing complexity of in-car electronics and the rapidly growing amount of sensors, actuators and electronic control units, places higher demands on high-speed data communication protocols. Safety critical systems need deterministic protocols with fault-tolerant behaviour. The need for on-board diagnostics calls for flexible use of bandwidth and an ever-increasing number of functions, necessitates a flexible means of extending the system.

None of the communication solutions available on the market until now have been able to fulfill all these demands.

To solve these problems, BMW together with several semiconductor companies have developed a new protocol for safety-critical applications in automotive vehicles.

The byteflight protocol combines the advantages of the familiar synchronous and asynchronous protocols and guarantees high data integrity at a data rate of 10 Mbps and an information update rate of 250 µs. Additional characteristics are collision-free bus access, message oriented addressing via identifiers, guaranteed latency for a certain number of high-priority messages, high flexibility, easy system extension, dynamic use of bandwidth and low system cost.

In order to reduce EMI, a physical layer solution using optical transmission was developed. In a star net configuration with an intelligent star coupler, communication is bidirectional on a single plastic optical fiber. The transceiver chip, the light-emitting diode and the photodiode are integrated into the optical connector.

Silicon for byteflight controllers, an intelligent star coupler and physical layer transceiver as well as several development tools are available. byteflight will be used by BMW in a series-production car within the next two years.

The features provided by the byteflight protocol are capable of solving many of today's in-car communication problems and could lead it to become a standard in the automotive industry.

byteflight in short

Protocol

  • New protocol: combination of time and priority controlled bus access
  • byteflight combines advantages of synchronous and asynchronous protocols.
  • Message format: ID, LEN, DATA (0..12), 15 bit CRC (h=6)
  • Collision free communication, no arbitration loss
  • Datarate: 10 Mbit/s gross, at full bus load > 5 Mbit/s net
  • Protocol- / hardware guaranteed latency for a certain amount of high priority messages, deterministic behaviour ensured by protocol
  • Analytical check of worst case latency for high priority messages composability
  • Flexible bus access of low priority messages as with asynchronous protocols (statistical behaviour)
  • Check of latencies for asynchronous messages is supported by a system simulation tool.

Topology, Physical Layer

  • Possible: Star, Bus, Cluster
  • Implemented todate: star topology with bidirectional (half-duplex) communication via POF (plastic optical fiber), transceiver chip with LED and photo diode integrated in optical connector, NRZ coding on TX/RX between byteflight controller and transceiver chip, bus diagnostic functions (optical transmission quality), optical wakeup function
  • possible: lower bitrates with electrical transceivers (e.g. CAN transceiver)

byteflight Development Tools

  • Bus analysers: online analysis, full trace of bus traffic, integrated harddisk, additional analog/digital channels, trigger logic, emulation of bus traffic, custom programming interface
  • System simulation tool Ptolemy: Modeling of byteflight Networks from a byteflight library, evaluation of system trade offs, test of protocol alternatives, protocol extensions, evaluation of system behaviour in error cases

Software in ECUs

  • Standardized communication software in all nodes
  • Safety critical SW tasks are triggered and synchronized by protocol regardless of the state of non safety critical SW tasks, safety critical SW tasks do not contain additonal interrupt service routine (ISR)
  • Non Safety Critical SW Tasks may contain several ISR's.

Possible applications

  • Automotive Applications: Passive and active safety, body applications
  • Combination with other non safety critical applications (body electronics): separation of bus traffic and SW tasks in safety critical and non safety critical parts
  • Aerospace industry
  • Industrial applications (Automation)

Available components

  • Standalone byteflight controller, HW implementation of byteflight Protocol, scalable buffer scheme: TX, Receive Buffer with ID filtering, FIFO Receive with ID mask/acceptance filter, 8/16 bit Intel/Motorola Bus-Interface
  • Motorola HC12BD32 with integrated byteflight controller
  • Active intelligent star coupler ASIC
  • Transceiver chip for optical transmission

Development partners concerning byteflight components:

  • Motorola, Transportation Systems Group
  • Elmos AG, Dortmund
  • Infineon AG (former Siemens semiconductor)
  • Tyco EC (former Siemens EC supplying connectors)
  • Weise GmbH (byteflight Bus Monitor)
  • CRST GmbH (byteflight Analyser)
  • Steinbeis Transferzentrum Prozeßautomatisierung, Prof. Etschberger (byteflight conformance test, byteflight Analyzer)