This article presents IDEA1, a SystemC-based system-level design and simulation framework for WSNs. It allows the performance evaluation (e.g., packet delivery rate, transmission latency and energy consumption) at high level, but with elaborate models of the hardware and software of sensor nodes. Many hardware components are modeled and the IEEE 802.15.4 standard is implemented. IDEA1 uses a clock-based synchronization mechanism to support simulations with cycle accurate communication and approximate time computation. The simulation results have been validated by a testbed of 9 nodes. The average deviation between the IDEA1 simulations and experimental measurements is 4.6%. The performances of IDEA1 have also been compared with NS-2. To provide a similar result (deviation less than 5%) at the same abstraction level, the simulation of IDEA1 is 2 times faster than NS-2. Moreover, with the hardware and software co-simulation feature, IDEA1 provides more detailed modeling of sensor nodes. Finally, IDEA1 is used to study a real-time industrial application in which a wireless sensor and actuator network is deployed on a vehicle to measure and control vibrations. By the simulation, some preliminary designs based on IEEE 802.15.4 protocols and two different hardware platforms are evaluated.