A testbed for fine-grained tracing of time sensitive behavior in wireless sensor networks

This paper introduces TRACELAB, a new testbed architecture that allows for fine-grained tracing of time sensitive behavior of low-power wireless embedded systems. Such traces help to systematically analyze code execution to find software errors, measure bounds for execution times, or to verify functional program properties. TRACELAB builds on the idea of GPIO tracing: by including short GPIO instructions into node applications, the program behavior can be traced in a minimally invasive manner, simultaneously on all observed nodes. TRACELAB enables fine-grained distributed tracing by overcoming the limits of existing testbed architectures with respect to timing accuracy and peak event rates. For that purpose, an existing testbed design is extended with a new data acquisition system that includes an FPGA chip for fast and deterministic data handling. To faithfully align distributed trace measurements, TRACELAB integrates a highly accurate wireless time distribution network. We build 31 TRACELAB observers and deploy them in an office environment and outdoors. Measurements using GPS precision timing show that TRACELAB (i) is able to trace events at rates of up to 108 events/s and (ii) aligns traces from different locations within 1 μs with an empirical probability of 99.9 %.