Time triggered protocol-fault tolerant serial communications for real-time embedded systems

This article discusses an advanced serial communications protocol which has been developed for applications which require highly dependable, or fault-tolerant operation. A typical such application would be automotive brake-by-wire or steer-by-wire systems where the system must be 'fail-operational' as it is safety critical. 'By-wire' systems transfer electrical signals down a wire instead of using a medium such as hydraulic fluid to transfer muscular energy. A conventional Antilock Braking System (ABS) is considered 'fail-silent'; if a fault in the electronic control system is detected, the control system is switched off, leaving the manual hydraulic back-up still operational. If no such hydraulic back-up is available (as in the case of a 'by-wire' system), the system must continue to function in the event of a fault occurring. The automotive industry has identified many good reasons to develop 'by-wire' systems; reduction in parts count, removal of hydraulic system, improved maintenance, increased performance and functionality, increased passive safety by removal of mechanical linkages to passenger compartment, fuel economy, etc. Although there are several non-trivial challenges which must be overcome before 'by-wire' systems become the mainstream, there are many compelling reasons for the technology to be introduced and so it is expected that they'll be overcome relatively quickly. The Time Triggered Protocol (TTP) overcomes the challenge of fault-tolerant distributed embedded processing.