Hardware-Based Load Value Trace Filtering for On-the-Fly Debugging

Abstract

________________________________________________________________________Capturing program and data traces during program execution unobtrusively on-the-fly is crucial in debugging and testing of cyber-physical systems. However, tracing a complete program unobtrusively is often costprohibitive, requiring large on-chip trace buffers and wide trace ports. This paper describes a new hardwarebased load data value filtering technique called Cache First-access Tracking. Coupled with an effective variable encoding scheme, this technique achieves a significant reduction of load data value traces, from 5.86 to 56.39 times depending on the data cache size, thus enabling cost-effective unobtrusive on-the-fly tracing and debugging.

mcfTRaptor: Toward unobtrusive on-the-fly control-flow tracing in multicores

“…ARM's new Embedded Trace Macrocell version four (ETMv4) proposed for ARMv7 ISA employs branch predictor to reduce the control-flow trace port bandwidth, reporting $0.35 bits per instruction [14]. For load value traces, Uzelac and Milenkovic [15,16] introduced cache first-access tracking mechanism (c-fiat) that reduces the trace size between 5.8 and 56 times, depending on the cache size. However, these techniques have been demonstrated for uniprocessors only.…”

“…In such cases, control-flow traces and program check-pointing can be used to pinpoint the program segment for which a full data trace is needed. Capturing and compression of data traces in real-time is out of scope of this paper, but methods described by Uzelac and Milenkovic [16] can be extended to multicores.…”

“…11 12 13 14 15 16 17 18 19 20 21 22 23 24 length (field) [bits]CDF for bCnt, |diffTA|, & diffCC: Cumulative distribution function of the minimum length for bCnt, |diffTA|, and diffCC fields.…”