Inter-processor communication and synchronization are critical problems in embedded multiprocessors. In order to achieve high-speed communication and low-latency synchronization, most recent designs employ dedicated hardware engines to support these communication protocols individually, which is complex, inflexible, and error prone. Thus, this paper motivates the optimization of inter-processor communication and synchronization by using application-specific instruction-set processor (ASIP) techniques. The proposed communication mechanism is based on a set of custom instructions coupled with a low-latency on-chip network, which provides efficient support for both data transfer and process synchronization. By using state-of-the-art ASIP design methodology, we embed the communication functionalities into a base processor, making the proposed mechanism feature ultra low overhead. More importantly, industry-standard compatible programming interfaces supporting both message-passing and shared-memory paradigms are exposed to end-users to ease the software porting. Experimental results show that the bandwidth of the proposed message-passing protocol can achieve up to 703 Mbyte/s @ 200 MHz, and the latency of the proposed synchronization protocol can be reduced by more than 81% when compared with the conventional approach. Moreover, as a case study, we also show the effectiveness of the proposed communication mechanism in a real-life embedded application, WiMedia UWB MAC.