On efficient silicon debug with flexible trace interconnection fabric

Abstract

Trace-based debug solutions facilitate to eliminate bugs escaped from pre-silicon verification and have gained wide acceptance in the industry. Generally speaking, a number of "key" signals in the circuit are tapped, but not all of them can be observed at the same time due to the limited trace bandwidth. Therefore, a trace interconnection fabric is utilized to output either a subset of signals with multiplexor (MUX) network or compressed signatures with XOR network to the trace memory/port in each debug run. However, both kinds of trace interconnection fabrics have limitations. On one hand, with MUX-based fabric, the visibility of the circuit is limited and it requires many debug runs to locate errors. On the other hand, with XOR-based fabric, typically clean "golden vectors" (i.e, without unknown bits) are required so that signatures are not corrupted. In this paper, we propose a flexible trace interconnection fabric design that is able to overcome the above limitations, at the cost of little extra design-for-debug hardware. Experimental results on benchmark circuits demonstrate the effectiveness of the proposed technique.