The design of Industrial Wireless Sensor Network (IWSN) stacks requires the adoption of Real Time Operation System (RTOS). Challenges exist especially in timing integrity and multi-processor support. As a solution, the authors propose an RTOS-based architecture for IWSN stacks with multi-processor support. It offers benefits in terms of platform independency, product life cycle, safety and security, system integration complexity and performance scalability. An implemented wireless HART stack has proven the feasibility of the proposed architecture in practical product design.