In Part 3 of this series, we did a code review of โltloopโ, a utility firmware application that uses the BMC to do out-of-band stress tests of PCI Express ports. In this article, we begin to examine a more general-purpose application that uses JTAG to extract register, memory and IO contents of the target. This On-Target Diagnostic (OTD), called โlibtestโ, is used by ASSET to test the functionality of run-control on new targets.