Cap the heap at the cart-region boundary#2
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__StackLimit is pico-sdk's _sbrk heap ceiling. Including LENGTH(ROM_IN_RAM) let the heap grow through the entire ROM_IN_RAM mirror -- the region the m68k executes over the cartridge bus. Boot-time allocations (the settings library alone mallocs ~13 KB) and runtime FatFs LFN buffers then silently overwrite the served cartridge code, crashing the ST with bombs / black screens that vary per build with static layout. Drop the + LENGTH(ROM_IN_RAM) so the heap is capped at the RAM/cart boundary and malloc fails cleanly (pico-sdk panics on failed malloc) instead of corrupting the m68k image.
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Problem
In
rp/src/memmap_rp.ld, the heap ceiling is:__StackLimitis what pico-sdk's_sbrkuses to bound the heap. IncludingLENGTH(ROM_IN_RAM)lets the heap grow straight through theROM_IN_RAMmirror — the region the m68k executes from over the cartridge bus.Boot-time allocations (the settings library alone mallocs ~13 KB) and runtime FatFs LFN buffers then silently overwrite the served cartridge code, crashing the ST with bombs / a black screen. As with the array-alignment issue, the exact trigger shifts with static layout, so it is intermittent and hard to trace.
Fix
Drop
+ LENGTH(ROM_IN_RAM)so the heap is capped at the RAM/cart boundary. A failed allocation then panics cleanly (pico-sdk panics on OOM) instead of corrupting the m68k image:Verified in a downstream app whose settings-library boot mallocs were overrunning the cart region: with the heap capped, the region stays intact and any genuine OOM surfaces as a clean panic. Apps that need more heap should reclaim RAM rather than borrow the cartridge mirror.