An LZ77-style bit-level compression for trace data compaction

Online tracing is a powerful technique for monitoring and debugging embedded processors. The amount of data produced by tracing is enormous. Thus, an on-the-fly trace data reduction close by its source is extremely valuable. Trigger-driven filtering and a compressed trace representation are popular measures to take. While effective methods for the compression of branch target addresses in instruction traces are known, modern processors also produce extensive execution bit streams to log the execution of conditional instructions. This paper proposes an LZ77-style compressor for these bit streams. In contrast to classic implementations, it operates on the bit level. It is demonstrated that this compressor is effective even when using a small dictionary. This allows an implementation within an FPGA close by the source or even on the same chip as the trace source. It is also shown that the compressor can keep pace with practically relevant trace data sources.