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eSi-RISC is a configurable CPU architecture from Ensilica. It is available in five implementations: the eSi-1600, eSi-1650, eSi-3200, eSi-3250 and eSi-3260. The eSi-1600 and eSi-1650 feature a 16-bit data-path, while the eSi-32x0s feature 32-bit data-paths. Each of these processors is licensed as soft IP cores, suitable for integrating into both ASICs and FPGAs.
While there are many different 16 or 32-bit Soft microprocessor IP cores available, eSi-RISC is the only architecture licensed as an IP core that has both 16 and 32-bit implementations.
Unlike in other RISC architectures supporting both 16 and 32-bit instructions, such as ARM/Thumb or MIPS/MIPS-16, 16 and 32-bit instructions in the eSi-RISC architecture can be freely intermixed, rather than having different modes where either all 16-bit instructions or all 32-bit instructions are executed. This improves code density without compromising performance. The 16-bit instructions support two register operands in the lower 16 registers, whereas the 32-bit instructions support three register operands and access to all 32 registers.
eSi-RISC includes support for Multiprocessing. Implementations have included up to seven eSi-3250's on a single chip.