transition to $$brk_reset,$$error in the startup file (*.asm) occurs when the brk instruction (0xffff) is executed. addresses to which no instruction is assigned are filled with 0xffff, so it seems that for some reason this address was executed and transitioned to $$brk_reset, $$error. as a possible cause, ・interrupt vector is not defined ・a branch destination (function) such as an indirect call is not defined ・interrupts are enabled within interrupt functions that disable multiple interrupts ・stack overflow occurs and so on. please check if any of the above apply. transitions can be easily checked using the branch trace function of the on-chip emulator.