ASSET-Intertech e-Book: Cache-as-RAM For Board Bring-up Of Non-Booting Circuit Boards

“Designers often face a catch-22. They have to diagnose a non-booting prototype, but they can’t debug anything without some software running on the circuit board,” said Larry Osborn, technical product manager for ASSET and author of the new e-book. “Fortunately, run-control tools can help designers employ CPU cache-as-RAM methods to find faults like defects in the memory controller or in its link to the CPU. Simply applying power to a prototype doesn’t help the engineer much because when the board won’t boot, he doesn’t know whether it’s a hardware or software problem.”



Executive Summary



Design engineers often must diagnose and debug circuit boards that will not boot the bare metal firmware or have no BIOS at all. And, without some sort of software running on the board, comprehensively diagnosing structural and functional deficiencies is practically impossible. One effective way to get around this catch-22 is to use the on-chip cache memory in the board’s processor instead of discrete on-board RAM memory space to execute diagnostic and test routines which will identify faults that could be causing boot failures, such as failures in the memory controller or the links to it. Instead of simply powering up the board and discovering it won’t boot, a relatively short, yet deliberate step-by-step methodology will actually save time by identifying hardware faults that could prevent the boot process. In addition, the circuitry on a prototype board might be damaged if power were applied to it without an initial test phase. Cache-as-RAM techniques could be incorporated into this process because they are an effective way to bring up prototypes and verify hardware functionality without relying on fully functional and tested operating firmware.



Although executing boot code out of cache is not a straightforward process, implementing cache-as-RAM debug can be accomplished effectively and quickly with the proper run-time control tools that allow designers to quickly deploy script-based and code-based debug routines to verify a board’s hardware functionality.