The adoption of Integrated Modular Avionics (IMA) architecture is a technological trend in the avionics industry due to its capability of supporting space and temporal partitioning, which is mandatory for systems with mixed criticality. However, combining partition allocation and schedule design for applications sharing hardware, software, and communication resources of the same computing platform while assuring temporal behavior is a complex task that requires adequate tools for system design and integration. This paper presents the main features of a model that has been developed for simultaneous partition allocation and schedule design, which allows for automatic adjustment of both applications distribution over the partitions and scheduling parameters toward performance optimization. In the proposed model, all the variables are integer and all constraints are formulated via linear equalities and inequalities. Therefore, this problem can be efficiently solved by many existing mixed integer linear programming algorithms. A set of timing constraints at both partition and task levels are established, and different optimization objective functions are provided. The results of a case study show that, if a solution exists, the proposed model can achieve a global optimum while guaranteeing that all the constraints are met.