Xilinx FPGAs in C for Free

When you think of developing with FPGAs, you usually think of writing Verilog or VHDL. However, there’s been a relatively recent trend to use C to describe what an FPGA should do and have tools that convert that to an FPGA. However, at least in the case of Xilinx parts, this capability is only available in their newest tool (Vivado), and Vivado doesn’t target the older lower-cost FPGAs that most low-cost development boards use.

[Sleibso] who blogs for Xilinx, has an answer. It turns out you can use the Vivado C compilation tools to generate code for older FPGAs; it just involves a less convenient workflow. Vivado (even the free version) generates unique files that the rest of the tool uses to pick up compiled C code. However, it also generates RTL (Verilog or VHDL) as a by-product, and you can import that into the older ISE tool (which has a perfectly fine free version) and treat it as you would any other RTL files.

There’s an example of using the Vivado tool in the video below. [Sleibso] points out that the video is three years old, and the talk about licensing on the video is out of date. The free tools now including this capability. [Sleibso] talks about using a Spartan 6, but the same split workflow should work with most devices ISE supports.

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Taking the Pulse (Width Modulation) of an FPGA

I like to think that there are four different ways people use FPGAs:

  1. Use the FPGA as a CPU which allows you to add predefined I/O blocks
  2. Build custom peripherals for an external CPU from predefined I/O blocks
  3. Build custom logic circuitry from scratch
  4. Projects that don’t need an FPGA, but help you learn

I’d bet the majority of FPGA use falls into categories one and two. Some FPGAs even have CPUs already built-in. Even without an onboard CPU, you can usually put a CPU “core” (think reusable library) into the chip. Either way, you can always add other cores to create UARTs, USB, Ethernet, PWM, or whatever other I/O you happen to need. You either connect them to a CPU on the chip, or an external one. With today’s tools, you often pick what you want from a list and then your entire project becomes a software development effort.

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FleaFPGA + Arduino Uno = FleaFPGAUno

Some things are better together: me and my wife, peanut butter and jelly, and FPGAs and Arduino Unos. Veteran hacker [Valentin Angelovski] seems to agree: the FleaFPGA Uno is his latest creation that combines an FPGA (a Lattice MachX02 700HC) with an Arduino-compatible CPU.

It’s a step-up model from the origional FleaFPGA. With a few other components thrown in (such as a HDMI and composite video output and a WiFi option), you have a killer combination for experimenting with FPGAs or building an embedded system. That is because the Arduino part frees the FleaFPGA Uno from the breadboard: you can easily program, control and interface with the FPGA over a serial line or a wireless link using the Arduino IDE. There is even support for Arduino shields (albeit only 3.3V ones), making it even more expandable. This would be an awesome starting point for a retro gaming system, as many 8-bit consoles can be easily emulated in an FPGA. [Valentin] is currently selling the boards directly, and they are very reasonably priced at $50 or $60 for the WiFi version.

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Stuffing Macs Into FPGAs

A few years ago, [Steve] of Big Mess ‘O Wires fame stuffed one of the first Macintosh computers into an FPGA. While the project worked and was able to run System 6 on a virtual CPU, there were a few problems: it wasn’t exactly stable, and there was no support for a keyboard, sound, SCSI, or serial ports.

Now, there’s a new tiny FPGA board around, and this one is perfectly designed to fit the original Macintosh on it. It’s much more stable, and there is a floppy disk emulator on the horizon, just so you won’t have to deal with all those 400k 3.5″ disks anymore.

[Steve]’s brand new Mac Plus is based on the MiST board, an FPGA board that was originally designed to emulate the first Amigas and the Atari SE on an FPGA and a separate ARM CPU. There’s already been a lot of classic computers ported to the MiST, and the classic all-in-one Macs are the last project that’s left.

In the video below, you can see the MiST board running the classic System 6 at SVGA resolution. That means MacPaint and Shufflepuck in one compact board using modern hardware.

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FPGAs For The Raspberry Pi

FPGA development has advanced dramatically in the last year, and this is entirely due to an open-source toolchain for Lattice’s iCE40 FPGA. Last spring, the bitstream for this FPGA was reverse engineered and a toolchain made available for anything that can run Linux, including a Raspberry Pi. [Dave] from Xess thought it was high time for a Raspberry Pi FPGA board. With the help of this open-source toolchain, he can program this FPGA board right on the Raspberry Pi.

The inspiration for [Dave]’s board came from the XuLA and StickIt! boards that give the Raspberry Pi an FPGA hat. These boards had a problem; the Xilinx bitstreams had to be compiled on a ‘real’ PC and brought over to the Raspberry Pi world. The new project – the CAT Board – brings an entire FPGA dev kit over to the Raspberry Pi.

The hardware for the CAT Board is a Lattice iCE-HX8K, 32 MBytes of SDRAM, a serial configuration flash, LEDs, buttons, DIP switches, grove connectors, and SATA connectors (although [Dave] is just using these for differential signals; he doesn’t know if he can get SATA hard drives to work with this board).

Despite some problems with his board house, [Dave] eventually got his FPGA working, or at least the bitstream configuration part, and he can blink a pair of LEDs with a Raspberry Pi and programmable logic. The Hello World for this project is done, and now the only limit is how many gates are on this FPGA.

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Open Source FPGA Pi Hat

Over on Hackaday.io, [Dave Vandenbout] has posted the CAT board, a Raspberry Pi daughterboard hat that features a Lattice FPGA, 32 MB of RAM, EEPROM, and a few Grove and PMOD connectors. The CAT takes advantage of the open source tool chain available for Lattice including the Python-based MyHDL (although, you could just use Verilog directly, if you prefer) and Icestorm. One interesting point: you can run the tool chain on the Raspberry Pi, resulting in a self-contained and largely portable FPGA development environment.

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ARMs and FPGAs Make for Interesting Dev Boards

Tiny Linux computers are everywhere, and between BeagleBones, Raspberry and Banana Pis, and a hundred other boards out there, there are enough choices to go around. There is an extremely interesting ARM chip from Xilinx that hasn’t seen much uptake in the field of tiny credit-card sized computers: the Zynq. It’s an ARM Cortex-A9 coupled with an FPGA. It’s great for building peripherals that wouldn’t normally be included on a microcontroller. With Zynq, you just instantiate the custom bits in the FPGA, then interface them with a custom Linux driver. Thanks to CrowdSupply, there’s now a board out there that brings this intriguing chip to a proper development platform. It’s called the Snickerdoodle, and if you’ve ever wanted to see the capabilities of an FPGA tightly coupled to a fast processor, this is the board to watch.

The core of the Snickerdoodle is a Xilinx Zynq that features either a 667 MHz ARM Cortex A9 and a 430k gate FPGA (in the low-end configuration) or an 866 A9 and 1.3M gate FPGA. This gives the Snickerdoodle up to 179 I/O ports – far more than any other tiny Linux board out there.

Fully loaded, the Snickerdoodle comes with 2.4 and 5GHz WiFi, Bluetooth, 1GB of RAM, and an ARM Cortex A9 that should far surpass the BeagleBone and Raspberry Pi 2 in capabilities. This comes at a price, though: the top-shelf Snickerdoodle has a base price of about $150.

Still, the power of a fast ARM and a big FPGA is a big draw and we’re expecting a few more of these Zynq boards in the future. There are even a few projects using the Zynq on hackaday.io, including one that puts the Zynq in a Raspberry Pi-compatible footprint. That’s exceedingly cool, and we can’t wait to see what people will build with a small, fast ARM board coupled to an FPGA.