Domain-specific accelerators (DSAs) are becoming increasingly common in systems-on-chip (SoCs). A DSA provides higher performance per watt than a general-purpose processor by optimizing the specialized function it implements. Examples of DSAs include compression/decompression units, random number generators and network packet processors. A DSA is typically connected to the core complex using a standard IO interconnect, such as an AXI bus.
article: https://www.sifive.com/blog/fast-access-to-accelerators-enabling-optimized-data-transfer-with-risc-v