def __insn_repl(self, addr, replacement):
        original_insn = struct.unpack("!I", self.dev.rxcpu.tr_read(addr, 1))[0]
        self.dev.rxcpu.tr_write_dword(addr, replacement)
        return original_insn

        try:
            self._breakpoints[addr] = original_insn
        except:
            self._breakpoints = {addr: original_insn}