Nuclei Processor

Nuclei processor core are following and compatible to RISC-V standard architecture, but there might be some additions and enhancements to the original standard spec.

Click Nuclei Spec to learn more about Nuclei RISC-V Instruction Set Architecture.


Nuclei provides the following RISC-V IP Products for AIoT:

  • N100 series: Designed for mixed digital and analog, IoT or other extremely low-power and small area scenarios, which is the perfect replacement of traditional 8051 cores.

  • N200 series: Designed for ultra-low power consumption and embedded scenarios, perfectly replaces the arm Cortex-M series cores.

  • N300 series: Designed for extreme energy efficiency ratio, requiring DSP and FPU features, as IoT and industrial control scenarios.

  • 600 series and 900 series: Fully support Linux for high-performance edge computing and smart AIoT.


  • N100 series is not supported by NMSIS and Nuclei SDK

NMSIS in Nuclei SDK

This Nuclei SDK is built based on the NMSIS framework, user can access NMSIS Core API, NMSIS DSP API and NMSIS NN API provided by NMSIS.

These NMSIS APIs are mainly responsible for accessing Nuclei RISC-V Processor Core.

The prebuilt NMSIS-DSP and NMSIS-NN libraries are also provided in Nuclei SDK, see NMSIS/Library/ folder.


  • To support RT-Thread in Nuclei-SDK, we have to modify the startup_<device>.S, to use macro RTOS_RTTHREAD defined when using RT-Thread as below:

    #ifdef RTOS_RTTHREAD
        // Call entry function when using RT-Thread
        call entry
        call main
  • In order to support RT-Thread initialization macros INIT_XXX_EXPORT, we also need to modify the link script files, add lines after `` (.rodata .rodata.)`` as below:

    . = ALIGN(4);
    *(.rodata .rodata.*)
    /* RT-Thread added lines begin */
    /* section information for initial. */
    . = ALIGN(4);
    __rt_init_start = .;
    __rt_init_end = .;
    /* section information for finsh shell */
    . = ALIGN(4);
    __fsymtab_start = .;
    __fsymtab_end = .;
    . = ALIGN(4);
    __vsymtab_start = .;
    __vsymtab_end = .;
    /* RT-Thread added lines end */

SoC Resource

Regarding the SoC Resource exclude the Nuclei RISC-V Processor Core, it mainly consists of different peripherals such UART, GPIO, I2C, SPI, CAN, PWM, DMA, USB and etc.

The APIs to access to the SoC resources are usually defined by the SoC Firmware Library Package provided by SoC Vendor.

In Nuclei SDK, currently we just required developer to provide the following common resources:

  • A UART used to implement several stub functions for printf function

    • When using newlib library, please check stub functions list in SoC/evalsoc/Common/Stubs/newlib

    • When using libncrt library, please check stub functions list in SoC/evalsoc/Common/Stubs/libncrt

    • When using iar dlib library, please check stub functions list in SoC/evalsoc/Common/Stubs/iardlib

  • Common initialization code defined in System_<Device>.c/h in each SoC support package in Nuclei SDK.

  • Before enter to main function, these resources must be initialized:

    • The UART used to print must be initialized as 115200 bps, 8bit data, none parity check, 1 stop bit

    • ECLIC MTH set to 0 using ECLIC_SetMth, means don’t mask any interrupt

    • ECLIC NLBits set to __ECLIC_INTCTLBITS, means all the nlbits are for level

    • Global interrupt is disabled


  • If you want to learn more about SoC, please click SoC

  • If you want to learn more about Board, please click Board

  • If you want to learn more about Peripheral, please click Peripheral