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| Designer | Altera/Intel |
|---|---|
| Bits | 32-bit |
| Design | RISC |
| Endianness | Little-Endian |
| Open | No |
| Registers | |
| General-purpose | 32 |
Nios II is a32-bit embedded processor architecture designed specifically for theAltera family offield-programmable gate array (FPGA)integrated circuits. Nios II incorporates many enhancements over the originalNios embedded processor architecture, making it more suitable for a wider range of embedded computing applications, fromdigital signal processing (DSP) to system-control. Nios II is a successor to Altera's first configurable16-bit embedded processor Nios, introduced in 2000.[1] Intel announced the discontinuation of Nios II in 2023, with its successor beingNios V, based on theRISC-V architecture.[2]
Like the original Nios, the Nios II architecture is aRISCsoft-core architecture which is implemented entirely in the programmable logic and memory blocks of Altera FPGAs. Unlike its predecessor it is a full32-bit design:
The soft-core nature of the Nios II processor lets the system designer specify and generate a custom Nios II core, tailored for his or her specific application requirements. System designers can extend the Nios II's basic functionality by, for example, adding a predefinedmemory management unit (MMU), or defining custom instructions and custom peripherals.
Similar to native Nios II instructions, user-defined instructions accept values from up to two 32-bit source registers and optionally write back a result to a 32-bit destination register. By using custom instructions, the system designers can fine-tune the system hardware to meet performance goals and also the designer can easily handle the instruction as a macro inC.
For performance-critical systems that spend most CPU cycles executing a specific section of code, a user-defined peripheral can potentially offload part or all of the execution of a software-algorithm to user-definedhardware logic, improving power-efficiency or application throughput.
Introduced withQuartus 8.0, the optional MMU enables Nios II to run operating systems which require hardware-based paging and protection, such as theLinux kernel. Without an MMU, Nios is restricted to operating systems which use a simplified protection and virtual memory-model: e.g.,μClinux andFreeRTOS.
Introduced with Quartus 8.0, the optional MPU provides memory protection similar to that provided by an MMU but with a simpler programming model and without the performance overhead associated with an MMU.
Nios II classic is offered in 3 different configurations: Nios II/f (fast), Nios II/s (standard), and Nios II/e (economy).Nios II gen2 is offered in 2 different configurations: Nios II/f (fast), and Nios II/e (economy).
The Nios II/f core is designed for maximum performance at the expense of core size. Features of Nios II/f include:
Nios II/s core is designed to maintain a balance between performance and cost. This core implementation is not longer supported for Altera Quartus II v.17 and newer. Features of Nios II/s include:
The Nios II/e core is designed for smallest possible logic utilization of FPGAs. This is especially efficient for low-cost Cyclone II FPGA applications. Features of Nios II/e include:
Nios II uses the Avalonswitch fabric as the interface to its embedded peripherals. Compared to a traditional bus in a processor-based system, which lets only one bus master access the bus at a time, the Avalon switch fabric, using a slave-side arbitration scheme, lets multiple masters operate simultaneously.
Development for Nios II consists of two separate steps: hardware generation and software creation.
Development is hosted inside an Altera application called the Embedded Design Suite (EDS). The EDS contains a complete integrated development environment to manage both hardware and software in two separate steps:
Nios II hardware designers use the Qsys system integration tool, a component of the Quartus-II package, to configure and generate a Nios system. The configurationgraphical user interface (GUI) allows users to choose the Nios-II's feature-set, and to add peripheral and I/O-blocks (timers, memory-controllers, serial interface, etc.) to the embedded system. When the hardware specification is complete, Quartus-II performs the synthesis, place & route to implement the entire system on the selected FPGA target.
Qsys is replacing the older SOPC (System-on-a-Programmable-Chip) Builder, which could also be used to build a Nios II system, and is being recommended for new projects.[3]
A separate package, called the Embedded Design Suite (EDS), manages the software development. Based on theEclipse IDE, the EDS includes a C/C++ compiler (based on theGNU toolchain), debugger, and an instruction-set simulator. EDS allows programmers to test their application in simulation, or download and run their compiled application on the actual FPGA host.
Because the C/C++ development-chain is based onGCC, the vast majority ofopen source software forLinux compiles and runs with minimal or no modification. Third-party operating-systems have also been ported to Nios II. These include MicriumMicroC/OS-II,eCos,Segger Microcontroller embOS,ChibiOS/RT,μCLinux andFreeRTOS.
GCC 15 removed support for Nios II processors due to Nios II's discontinuation.[4]
Nios II is comparable toMicroBlaze, a competingsoftcore CPU for theXilinx family of FPGA. Unlike MicroBlaze, Nios II is licensable for standard-cellASICs through a third-party IP provider,Synopsys Designware. Through the Designware license, designers can port Nios-based designs from an FPGA-platform to a mass production ASIC-device.