The automatic detection and use of project local .ldt files is an integral part of the managed linker script mechanism. For more details, please see chapter 18, "Memory Configuration and Linker Scripts" in the MCUXpresso IDE v11.0 User Guide. In particular, section 18.3 "How are Managed Linker Scripts Generated?" and section 18.4, "FreeMarker Linker Script Templates".
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MCUXpresso IDE Support