Online cache state dumping for processor debug

Post-silicon processor debugging is frequently carried out in a loop consisting of several iterations of the following two key steps: (i) processor execution for some duration, followed by (ii) dumping out of the processor's internal state into an external logic analyzer for further offline processing. Internal state of the processor is dominated by the L2 cache. During the process of dumping the cache content, the processor's execution is halted so that the state can be faithfully reproduced offline. In order to reduce the duration for which the processor is halted, and indirectly reduce debug time, we propose two online cache dumping strategies, retransmit non-dumped line (RNL) and dump history table (DHT), with the objective of transferring the cache contents while the processor is executing, and yet maintaining fidelity of the dumped data. For typical experimental debug scenarios, we observe that the effective dump times are reduced to between 0.01% and 3.5% of the original times. We also employ compression to reduce the cache content transfer time and logic analyzer space. Our experiments indicate an average compression ratio of 59.2%.