When the Debugger Lies

I've spent the last few weeks working with the security architecture of the nRF54L series from Nordic Semiconductor (in case you missed it, I recently joined Nordic!). While doing so, I have engaged my typical low-level learning technique of eschewing writing firmware for manually poking at registers using the debugger. A few nights ago I found myself observing unexpected values in memory when working with the key management unit. It turned out to be a familiar issue, but one that requires an understanding of the internal system on chip (SoC) components, and how the debugger interacts with them, to diagnose.