2021 July 13 12:43

Yesterday I learned about the Raspberry Pi Pico.

This is a $4 board that, unlike the other Raspberry Pi offerings, is based on a dual-core Cortex-M0+ microcontroller chip – the RP2040 – designed by the Raspberry Pi Foundation.

The blog post announcing its introduction has a nice overview, and talks a bit about why the Raspberry Pi Foundation wanted to enter the microcontroller space with their own chip and board.

The specifications and documentation for the board and chip are both very complete and readable, and the RP2040 has a ROM bootloader (“PICOBOOT”) that was thoughtfully designed – unlike all the other ROM bootloaders out there! I think it would be very easy to get muforth to talk to it, and I wouldn’t have to “roll my own” USB chat code, which is pretty overwhelming to do on all the different chip families and USB OTG/device implementations out there.

I’m excited about this board and chip!

2021 July 07 20:32

How did I spend my day? I broke out two big “howto” documents that were buried in the 2018 journal page and turned them into freestanding pages, and then I wrote about how Twitter Cards work and how I’m using them on this site and on muforth.

Read about:

2021 January 09 12:49

Hey everyone! Happy 2021!

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

More fun with RISC-V

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.

Update: 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).

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.

These are all interesting alternatives to SiFive’s HiFive1 Rev B. The HiFive1 costs $59, and runs much faster (320 MHz vs 108 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.