Board support crate for the Longan Nano board

• Rust 1.36 or a newer toolchain. e.g. rustup default stable

• rust-std components (pre-compiled core crate) for the RISC-V target. Run:

rustup target add riscv32imac-unknown-none-elf

• RISC-V toolchain (e.g. from SiFive)

One of:

• dfu-util
• openocd for GD32VF103
• RV-LINK

If you have a GD32VF103CB chip on your board, edit .cargo/config and replace memory-c8.x with memory-cb.x.

To build all the provided examples run

cargo build --examples --release --all-features

The GD32VF103 contains a DFU compatible bootloader which allows to program the firmware of your longan-nano without additional hardware like a JTAG adapter; instead just using an ordenary USB-C cable. You can use dfu-util or the vendor supplied tool to flash the firmware.

Unfortunately, some versions of this chip shipped with a buggy bootloader and it won't report the correct parameters to flash it sucessfully. As of May 2020, the most recent version of dfu-util from the git repository contains a workaround. Make sure you use an up-to-date version. See this issue for details.

Steps to flash an example via DFU:

1. Extract the binary

riscv-nuclei-elf-objcopy -O binary target/riscv32imac-unknown-none-elf/release/blinky firmware.bin

2. Flash using dfu-util:

Keep the BOOT0 button pressed while power-up or while pressing and releaseing the reset button. Then run

dfu-util -a 0 -s 0x08000000:leave -D firmware.bin

Ensure that dfu-util uses a page size of 1024; either because your GD32VF103 has a bootloader without the the aforementioned bug, or because the output reads

[...]
Device returned transfer size 2048
DfuSe interface name: "Internal Flash  "
Found GD32VF103, which reports a bad page size and count for its internal memory.
Fixed layout based on part number: page size 1024, count 128.
Downloading to address = 0x08000000, size = 23784
[...]

Start openocd assuming you have Sipeed JTAG adapter:

/path/to/openocd -f sipeed-jtag.cfg -f openocd.cfg

Run one of the examples:

cargo run --example blinky

or

cargo run --release --example ferris --features lcd

RV-LINK is a Chinese firmware, similar to Black Magic Probe (BMP). It supports the Longan Nano, allowing to use one Longan Nano board as a debug probe for another one. It can be built & flashed via PlatformIO. Check out the latest version to ensure that the code compiles:

> git clone https://gitee.com/zoomdy/RV-LINK
> cd RV-LINK
> git tag 
v0.0.1
v0.1
v0.2 # <- seems to be the latest tag, so let's check this out
> git checkout tags/v0.2 

PlatformIO allows building & flashing of firmware with a single command. To do so, the board needs to be in bootloader mode (DFU mode). The board boots to bootloader mode if the bootloader button is pressed while powering it up (e.g. by plugging it in). However, it is also possible to enter bootloader mode without un- and replugging the board: press the boot button, press the reset button, release the reset button and finally release the boot button while the board is plugged in.

> pio run -t upload # put the board in bootloader mode before

Once RV-LINK is flashed to your probe, connect the eight debug pins on the probe with the debug pins on the debug target. Ensure that you connect the pins according to this table:

After you connected the debug probe to your host, a new serial port shows up. You can connect GDB to this serial port as an extended-remote. For predictable behavior when multiple serial devices are present (and hence /dev/ttyACM0 is not necessarily the RV-LINK device), udev offers id symlinks. However you may also use /dev/ttyACM0 or even COMx if you run Windows.

> gdb
(gdb) target extended-remote /dev/serial/by-id/usb-RV-LINK_Longan_Nano_GD32XXX-3.0.0-7z8x9yer-if00

To flash the firmware, execute load in GDB:

> gdb target/remote/debug/demo
(gdb) target extended-remote /dev/ttyACM0
(gdb) monitor reset halt
(gdb) load
(gdb) monitor reset

To improve your workflow, you can put the aforementioned GDB commands in a debug.gdb file and add these lines to .cargo/config:

[target.riscv32imac-unknown-none-elf]
runner = 'gdb -command=debug.gdb'

This way cargo run --target riscv32imac-unknown-none-elf will automatically launch GDB, flash your firmware on the target and provide you with a full debug environment.

You can infer the current status of the board by observing the blinking pattern of the green LED:

Copyright 2019-2020 RISC-V team

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

Contribution to this crate is organized under the terms of the Rust Code of Conduct, the maintainer of this crate, the RISC-V team, promises to intervene to uphold that code of conduct.