DMA Transfer problem

You could create a linker section in those locations that prevent the linker from placing any sections in there. The lazy way to test this would be to dynamically allocate those two buffers using a malloc to ensure the linker doesn't put anything there. You can't pick a location that could potentially be used by the processor at run time without ensuring precautions are taken. So it's possible that your code is stomping on itself and causing things to go off in the weeds.