Functional Software-Based Self-Testing (SBST) of mi-croprocessors and processor-based testing of Systems-on-Chip (SoCs) have recently attracted the attention of test technology research community because they provide an effective alternative to other traditional testing and self-testing approaches. SBST allows at-speed functional test-ing of SoC cores with virtually no circuit overhead and limited dependence on external testers. Despite the impor-tance of peripheral control cores in SoCs (in terms of functionality and size), the applicability and limits of SBST on them have not been comprehensively studied. In this paper, we study the effectiveness of SBST on a broad class of communication peripherals. A systematic applica-tion of SBST on two popular peripheral cores (UART and Ethernet) demonstrates the effectiveness of SBST on SoCs with such cores.