This document discusses the software architecture for the Galileo Precise Timing Facility (PTF). The PTF generates Galileo System Time for synchronizing the Galileo satellite constellation and services. The software is divided into partitions running on LynxOS-178 and implements standards like ARINC-653 and the Galileo Software Standard. The architecture was validated using tools for requirements tracing, static analysis, memory profiling and test coverage. Developing the PTF software provided experience with high-assurance standards and partitioning approaches used in avionics.