HummingBird RISC-V Processor

HummingBird RISC-V 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 RISC-V Spec to learn more about Official RISC-V Instruction Set Architecture.

Introduction

Open source HummingBird RISC-V Processor provides the following RISC-V Cores for AIoT:

• E200 series: Designed for ultra-low power consumption and embedded scenarios, perfectly replaces the arm Cortex-M series cores.

NMSIS in HummingBird SDK

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

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

• NMSIS Core For HummingBird RISC-V
  • NMSIS Core API
    • Version Control
    • Compiler Control
    • Core CSR Register Access
    • Core CSR Encoding
    • Register Define and Type Definitions
    • CPU Intrinsic Functions
    • Peripheral Access
    • Systick Timer(SysTimer)
    • Interrupts and Exceptions
    • FPU Functions
    • System Device Configuration
    • ARM Compatiable Functions

The prebuilt NMSIS-DSP and NMSIS-NN libraries without dsp are also provided in HummingBird SDK, see NMSIS/Library/ folder.

Note

• To support RT-Thread in HBird-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
  #else
      call main
  #endif
  

• 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);
  *(.rdata)
  *(.rodata .rodata.*)
  /* RT-Thread added lines begin */
  /* section information for initial. */
  . = ALIGN(4);
  __rt_init_start = .;
  KEEP(*(SORT(.rti_fn*)))
  __rt_init_end = .;
  /* section information for finsh shell */
  . = ALIGN(4);
  __fsymtab_start = .;
  KEEP(*(FSymTab))
  __fsymtab_end = .;
  . = ALIGN(4);
  __vsymtab_start = .;
  KEEP(*(VSymTab))
  __vsymtab_end = .;
  /* RT-Thread added lines end */
  *(.gnu.linkonce.r.*)
  

SoC Resource

Regarding the SoC Resource exclude the HummingBird 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 HummingBird SDK, currently we just required developer to provide the following common resources:

• A UART used to implement the _write and _read stub functions for printf functions

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

  • PLIC interrupts are disabled and priorities set to 0

  • Global interrupt is disabled

Note

• 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