RE: nRF54LM20A external SWD programming issue and LM20 DK request

PjGlasso — Wed, 24 Jun 2026 18:24:23 GMT

I would add,

Most likely it is a Nordic integration/support issue at the boundary with SEGGER, not a simple “SEGGER is broken” issue.

Why:

SEGGER/J-Link can see and debug the LM20A core through the nRF54L15 DK: SWD-DP, Cortex-M33, secure debug, halt, registers, and memory access all work.
Nordic’s own nrfutil can program the same target through the same probe and wiring.
Nordic’s nRF Connect Programmer also sees the LM20A but cannot read/write it in this external-target setup.

That last point matters most. If it were only a SEGGER defect, you would expect Nordic Programmer—using Nordic’s intended tooling—to have a clearer working path. Since both the raw J-Link path and Nordic Programmer fail while nrfutil device program works, the likely split is:

Layer	Status
Physical SWD wiring / target power	Good
nRF54L15 DK onboard probe	Good
LM20A debug access	Good
Nordic device-programming protocol	Good via `nrfutil`
Generic J-Link RAMCode flash path	Fails
nRF Connect Programmer external-LM20A workflow	Fails

So the practical diagnosis is:

Nordic has a working programming implementation in nrfutil, but the same required LM20A flash initialization/algorithm is not successfully available through the J-Link Commander and nRF Connect Programmer external-target workflows you tested.

Who fixes what depends on the root cause:

If the LM20A needs a special flash-init sequence or Nordic-owned flash algorithm, Nordic needs to expose/support that path in Programmer or document it.
If SEGGER has the proper LM20A flash loader but it fails through the nRF54L15 DK OB probe, SEGGER needs to fix the J-Link RAMCode/flash-loader behavior.
If the DK’s onboard J-Link has a limitation for external LM20A targets, it is a Nordic DK firmware/integration issue.

Your Nordic contact is the right first escalation because:

they own the silicon and official workflow,
nrfutil already proves Nordic has a working route,
they can tell you whether an nRF54LM20 DK is required or whether the L15 DK external probe is officially supported for this target.

Then send the same evidence to SEGGER if Nordic says: “This external J-Link configuration should program LM20A.”

Please advise,
PJ Glasso