Software-defined acoustic modems (SDAMs) for underwater communication and networking have been an important research topic due to their flexibility and programmability. In this paper, we propose a reconfigurable platform for SDAMs based on the TI AM5728 processor, which integrates dual-core ARM Cortex-A15 CPUs and two TI C66x DSP cores. The signal processing and A/D, D/A for physical-layer communication are implemented in the DSP cores. The networking protocols and the application programs are implemented in the ARM cores. The proposed platform has the following characteristics: (1) Due to the high-performance dual-ARM cores, the whole NS3 network simulator can be run in the ARM cores. Network protocols developed in a software simulation platform (e.g., NS3 platform) can be seamlessly migrated to a hardware platform without modification. (2) A new physical-layer module associated with real acoustic channel is developed, such that a data packet generated from the application layer will be transmitted through a real acoustic channel. The results of networking experiments with five nodes are presented to demonstrate the effectiveness of the proposed platform.