RISC-V Summit

Traditional post silicon HW debug data collection involves the gathering of a snapshot of the design state at the point of failure using scan and an array dump. We propose a hardware mechanism called Debug Signal Trace (DST) that provides the ability to trace a set of design signals over multiple cycles leading to the point of the failure and to store the trace to an on-chip memory like SRAM, or to off-chip System memory. Post processing of the stored debug trace data not only gives debug visibility, but also the ability to build post silicon coverage points. Debug Signal Trace data is timestamped to correlate with instruction trace data. This extends the use-case to SW performance analysis. To ease adoption and usability, the DST control register definition mirrors that of the RISC-V Trace Control Interface which is familiar to the RISC-V debug community. DST supports signal compression to minimize the memory storage footprint. DST leverages the triggers specified in RISC-V Debug Spec while adding user configurable triggers using a select set of design signals.