Research

Designing Reliable Embedded System Using Xtensa Processors

Embedded computing systems have become pervasive in our day to day life and are used for a variety of tasks ranging from providing entertainment to assisting the functioning of key human organs. While reliability concerns in mission-critical embedded applications such as those in space shuttles, automotive braking systems and implanted medial devices are quite obvious, unexpected or premature failures even in non-critical applications, such as game boxes and portable video players can erode the reputation of the manufacturer and greatly diminish the widespread acceptability of new devices. The advent of more sophisticated embedded systems that support more powerful functions and the reliance on deep submicron process technologies for their fabrication have brought reliability concerns to the forefront. Designing a dependable embedded system on top of less reliable hardware platform poses great challenges for designers. Cost and energy sensitivity, as well as real time constraints, make some fault-tolerant techniques not viable for embedded system design. Many techniques to improve reliability can incur performance, energy, or cost penalty. It is very important to understand the design trade-offs to design a reliable embedded systems.

Variability in fabricated circuit primitive parameters due to the statistical nature of manufacturing process, signal integrity issues arising from internal, and external noise sources, such as cosmic ray, are the three important categories of reliability concerns facing the design of embedded systems hardware.

Techniques for coping with process variation, transient errors caused by crosstalk, or single event upset have been investigated in hardware domain. For example, approaches such as TMR (Triple Modular Redundancy), check-pointing and roll-back have been used for mission critical applications. However, such approach may not be viable for embedded applications, since real time constraint may be violated, or may be too expensive since embedded systems are very cost sensitive. Consequently, coping with reliability in embedded systems poses greater challenge for designers.

The proposed research is trying to tackle the reliability issues from very high level, starting from synthesis and customization of instruction set architecture, so that the reliability is taken into consideration in addition to conventional performance and power design goals. Tensilica's Xtensa processor may provide us a platform to explore different design techniques or design automation strategies. For example, instruction duplication may provide a cheaper solution comparing to hardware duplication, as a mean to ensure system reliability. Different ways of instruction synthesis may have dramatic impact on system reliability, similar to their impact on performance and power.

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