2021 January 09 12:49

Hey everyone! Happy 2021!

Let’s raise a glass and wish for a happy and productive 2021.

Recently I discovered both an interesting and very inexpensive RISC-V development board and a new-to-me family of RISC-V microcontrollers.

The board is the Sipeed Longan Nano, available from seeed studio and from some American distributors. (I bought a few from Mouser.) It is based on a GigaDevice GD32VF103CBT6 RISC-V microcontroller, costs about $5, and has a small 160x80 pixel LCD display in addition to the microcontroller.

GigaDevice started as a NOR flash company, and later entered the microcontroller market by making clones of ST Micro’s STM32 chips – the GD32 family.

In August 2019 GigaDevice unveiled the GD32VF RISC-V family, which replaces the Cortex-M ARM core in their GD32 devices with a 32-bit RISC-V core.

The GD32VF103CBT6 microcontroller on the Sipeed Longan Nano board sports a Nuclei “Bumblebee” RV32IMAC RISC-V core running at 108 MHz, 128KiB of flash, 32KiB of RAM, and various peripherals, including full-speed USB and CAN interfaces.

Interestingly, Nuclei have also published an open-source RISC-V core called Hummingbird. There is a book to go with it, but based on the covers shown in the project’s README it is unclear whether it has been published in English.

Both families of GigaDevice microcontrollers use ST Micro’s naming conventions, encoding into the part number the microcontroller family (“Baseline”, “Mainstream”, “Performance”, etc), flash size, package, and pin count. It is my understanding that they are pin-compatible with the ST Micro chips.

The Sipeed Longan Nano is not the only RISC-V board available from seeed studio. Two interesting options – both based on GD32VF103 microcontrollers – are the Wio Lite RISC-V (which includes an ESP8266 wifi module) and the SeeedStudio GD32 RISC-V Dev Board. Both are very affordable – less than $10.

I now wish I had bought a few of the GD32 RISC-V Dev Boards instead of the Longan Nano. Mouser carries two versions: the bare board ($6.90), and a kit that includes a board and a 240x320 LCD ($16.00).

These are all interesting alternatives to SiFive’s HiFive1 Rev B. The HiFive1 costs $59, and runs much faster (320 MHz), but it lacks many of the peripherals found on the GigaDevice chips, such as A/D converters and USB and CAN interfaces.

Read the 2020 journal.