International audienceThe paper discusses the performance and timing issues when migrating legacy avionics software to an Integrated Modular Avionic (IMA). The software in question is running on a mission computer equipped with several Motorola 68020 processors and two dual redundant databusses. A new hardware was introduced due to obsolescence problems. To reduce risk the legacy software should be migrated to the new hardware with possibly no changes. Therefore a software stack with standardised software interfaces according to IMA concepts was introduced that provides additionally the software interfaces required by the legacy software on top of IMA. On the original mission computer the software accesses the databusses directly via memory mapped I/O. This is no longer possible with a layered software architecture. With the implemented IMA software stack I/O is transmitted to a dedicated module via VME backplane. Calls to the hardware specific I/O drivers are handled on that module and responses replied back to the application software. The paper presents the results of timing and performance measurements with both the legacy and new software architectures on the respective target hardware.The points that need special interest when specifying the hardware, supplier provided software and when implementing the IMA software stack are discussed
