eSi-RISC is a configurable CPU architecture. It is available in five implementations: the eSi-1600, eSi-1650, eSi-3200, eSi-3250 and eSi-3264.^[1] The eSi-1600 and eSi-1650 feature a 16-bit data-path, while the eSi-32x0s feature 32-bit data-paths, and the eSi-3264 features a mixed 32/64-bit datapath. Each of these processors is licensed as soft IP cores, suitable for integrating into both ASICs and FPGAs.^[2]

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The main features of the eSi-RISC architecture are:^[3]

• RISC-like load/store architecture.
• Configurable 16-bit, 32-bit or 32/64-bit data-path.
• Instructions are encoded in either 16 or 32-bits.
• 8, 16 or 32 general purpose registers, that are either 16 or 32-bits wide.
• 0, 8, 16 or 32 vector registers, that are either 32 or 64-bits wide.
• Up to 32 external, vectored, nested and prioritizable interrupts.
• Configurable instruction set including support for integer, floating-point and fixed-point arithmetic.
• SIMD operations.
• Optional support for user-defined instructions, such as cryptographic acceleration .^[4]
• Optional caches (Configurable size and associativity).
• Optional MMU supporting both memory protection and dynamic address translation.
• AMBA AXI, AHB and APB bus interfaces.
• Memory mapped I/O.
• 5-stage pipeline.
• Hardware JTAG debug.

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.^[5]

The eSi-RISC toolchain is based on combination of a port of the GNU toolchain and the Eclipse IDE.^[6] This includes:

• GCC – C/C++ compiler.
• Binutils – Assembler, linker and binary utilities.
• GDB – Debugger.
• Eclipse – Integrated Development Environment.

The C library is Newlib and the C++ library is Libstdc++. Ported RTOSes include MicroC/OS-II, FreeRTOS, ERIKA Enterprise^[7] and Phoenix-RTOS^[8]