The growing demand for computing power in automotive applications can only be satisfied by embedded multi-core processors. Significant parts of such applications include OEM-owned legacy software, which has been developed for single-core platforms. While the OEM is faced with the issues of parallelizing the software and specifying the requirements to the ECU supplier, the latter has to deal with implementing the required parallelization within the integrated system. The Logical Execution Time (LET) paradigm addresses these concerns in a clear conceptual framework. We present here initial steps for applying the LET model in this respect: (1) Parallelization of legacy embedded control software, by exploiting existing inherent parallelism. The application software remains unchanged, as adaptations are only made to the middleware. (2) Using the LET programming model to ensure that the parallelized software has a correct functional and temporal behavior. The Timing Definition Language (TDL) and associated tools are employed to specify LET-based requirements, and to generate system components that ensure LET behavior. The work describes two conceptual ways for integrating TDL components in AUTOSAR.