Sipeed TANG Hex: A Raspberry Pi-Inspired FPGA

The Sipeed TANG Hex is a new Zynq 7020-based FPGA board recently launched by popular Chinese manufacturer Sipeed. It is yet another example of how the universal the Raspberry Pi form factor has found its way into the world the FPGA development boards.

Previously, we've seen the Zynqberry with its form factor modeled after the the Raspberry Pi 2 model B and how it's quite handy for being able to utilize your existing Raspberry shields with it.

The TANG Hex goes by a variety of names including Lychee HEX, Lychee Sugar, and Litchi candy. Which also keeps it in line with the Raspberry Pi in the sense of being named after a fruit (I'll admit, I'd never heard of the lychee fruit before now). Given its price point is as low as $72.47 in the US on AliExpress, it is by far the most affordable option for a development board boasting the Zynq-7020 chip in comparison to the Zybo Z7-20 for $239.20, the Pynq for $199.00, or the MicroZed 7020 for $265.00. Then considering its 1GB of DDR3 and 2GB of onboard NAND Flash, it's a really great deal.

The documentation is still pretty scarce so far for the TANG Hex board, the only source I found was on Sipeed's own file server where there are some zipped up project folders with a few different bitstreams and the contents of the image folder from a PetaLinux project. So you could use those to start running the TANG Hex headless, but as far as creating/adding your own design in Vivado or PetaLinux, you're on own creating a project from scratch using the schematic for reference.

The TANG Hex contrasts from the Zynqberry in that it follows the Raspberry Pi's first generation layout for the 26-pin GPIO header but still keeps the quad USB with Ethernet port setup as the second generation and later Pis. The TANG Hex also lacks an HDMI port, audio jack, DSI LCD connector, and CSI-2 camera connector in comparison to the Zynqberry.

However, the TANG Hex still routes its four USB ports and the Ethernet port to the Zynq via the same SMSC USB3320 hi-speed USB 2.0 ULPI transceiver chip as the ZynqBerry does. This means you could steal the Ethernet setup in the Vivado block design, device tree nodes, and kernel setup from the Zynqberry in order to create a new project for the TANG board (see here for a compiled list of Zynqberry resources I've done in the past). The available SD card slot on the TANG also means the same SD card preparation and boot process for an embedded Linux image can be followed as for the Zynqberry.

After digging around the schematic for a minute, I noticed that the serial interfaces available from the Zynq's MIO (UART from PS1, I2C, and GPIO) are routed to the 26-pin GPIO header. So that's where you would connect to then serial terminal for this board in contrast to using the microUSB port on the Zynqberry.

I also noticed a signal on the 26-pin GPIO header titled "FAN_SPEED" and "FAN_PWM," which I'm assuming there is fan PWM logic in the bitstreams and images from Sipeed's file server for the TANG Hex board. Which you should really consider a CPU fan for the Zynq-7020, it can get pretty hot during normal operation.

Overall, this is a really neat little board at a great price point. It's just not for a beginner, you'll need some prior experience to develop your own Vivado project and PetaLinux projects from scratch using the board's schematic.