Daniel Mangum found that GDB returned outdated, cached values after certain operations while debugging the Cortex-M33-based nRF54LM20. While JLinkGDBServer’s ReadMemAP command returned the correct result, the standard GDB x command continued to show old values. The issue was considered to be caused by caching in the J-Link software, as direct reads through the AHB-AP access port worked correctly. Disabling J-Link caching resolved the issue.
Why it matters
This finding shows that the memory values displayed during microcontroller debugging may not always reflect the device’s actual state. When tools accessing the same data produce different results, it can make it difficult to determine whether the problem lies in the hardware or the debugging chain, potentially leading to misdiagnosis. Comparing direct AHB-AP reads with GDB output provides developers with a concrete checkpoint for testing such inconsistencies. Although disabling caching resolves the issue, the fact that this remains a verified workaround rather than a permanent software fix leaves open the question of how the behavior on the J-Link side should be addressed.