A close approximation of the demo code on Sipeed Tang Nano boards as shipped.
/* When I wrote this, I had not been able to find the source of the bitstream */ /* which is preloaded onto the Sipeed Tang Nano "Little Bee" demo board (it */ /* has since turned up, the link in Sipeed's documentation was broken). This */ /* is notable for */ /* */ /* * Cycling its LEDs in the sequence off-G-B-R by sequencing each low */ /* * Cycle time is measured to be 4.19 seconds */ /* * Low time for each LED is 1.048 seconds (4.192 / 4) */ /* * Button B pressed (high) forces reset with all LEDs off (high) */ /* */ /* This is an attempt to reconstitute the missing project. It borrows heavily */ /* from https://github.com/andrsmllr/tang_nano_devbrd but chops out stuff */ /* which isn't strictly necessary and attempts to indicate what imports (in */ /* particular the clocks) actually are in terms of files. MarkMLl */ /* The LED signals could be conveniently redefined as a three-bit register. */ /* I've left them like this since that's how they're defined in the donor */ /* project, although I have corrected their order so that the sequence is the */ /* more conventional off-R-G-B, and used button A to reverse the sequence. */
The serial interface chip on the Tang Nano board is underpowered, and grossly inadequate when plugged directly into a modern computer. Assume that for reliable operation you need a USB v1 hub, although many other cheap hubs have such poor performance that they might be suitable.
I can't speak for Windows, but on Linux you need to add (or enable the lines in) two additional configuration files before plugging the board in:
/etc/modprobe.d/tang-nano.conf # Blacklisted to allow the Gowin programmer to run. blacklist ftdi_sio
and
/etc/udev/rules.d/51-tang-nano.rules
# Remember to udevadm control --reload and to blacklist/remove the ftdi_sio the module.
KERNEL=="ttyUSB*", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6010", GROUP="plugdev", MODE:="0660"
SUBSYSTEMS=="usb", ATTRS{idVendor}=="0403", ATTRS{idProduct}=="6010", ATTRS{product}=="Sipeed-Debug", GROUP="plugdev", MODE="0660"
# NOTE: This illicitly uses an FTDI identifier, so should be left disabled.
If you don't have those, don't reload the udev rules, or don't remove ftdi_sio after adding/enabling the files, the Gowin programmer will attempt to run rmmod to remove ftdi_sio... this will of course fail for an unprivileged user.
So to wrap up, I say again: TWO configuration files, RELOAD udev, and REMOVE ftdi_sio.