FPGA to Ethernet Direct

When [iliasam] needed an Ethernet connection, he decided to see how much of the network interface he could put in the FPGA logic. Turns out that for 10 Base-T, he managed to get quite a bit inside the FPGA. His original post is in Russian, but automatic translation makes a passable attempt at converting to English.

This is a classic trade off all FPGA designers face: how much external logic do you use for a particular design. For example, do you add memory to the PCB, or use FPGA resources as memory? Each has its advantages and disadvantages (that’s why it is a trade off). However, if you are trying to keep things cheap, slashing external circuitry is often the way to go.

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32C3: A Free and Open Source Verilog-to-Bitstream Flow for iCE40 FPGAs

[Clifford] presented a fully open-source toolchain for programming FPGAs. If you don’t think that this is an impressive piece of work, you don’t really understand FPGAs.

The toolchain, or “flow” as the FPGA kids like to call it, consists of three parts: Project IceStorm, a low-level tool that can build the bitstreams that flip individual bits inside the FPGA, Arachne-pnr, a place-and-route tool that turns a symbolic netlist into the physical stuff that IceStorm needs, and Yosys which synthesizes Verilog code into the netlists needed by Arachne. [Clifford] developed both IceStorm and Yosys, so he knows what he’s talking about.

What’s most impressive is that FPGAs aren’t the only target for this flow. Because it’s all open source and modifiable, it has also been used for designing custom ASICs, good to know when you’re in need of your own custom silicon. [Clifford]’s main focus in Yosys is on formal verification — making sure that the FPGA will behave as intended in the Verilog code. A fully open-source toolchain makes working on this task possible.

If you’ve been following along with [Al Williams]’s FPGA posts, either this introduction or his more recent intermediate series that are also based on the relatively cheap Lattice iCEStick development kit, this video is a must-watch. It’s a fantastic introduction to the cutting-edge in free FPGA tools.

Not Ready for FPGAs? Try a CPLD

[Kodera2t]  wanted to experiment with programmable logic. Instead of going with an FPGA board, he decided to build his own CPLD (complex programmable logic device) board, with a built-in programmer. The CPLD is a Xilinx 9536 which is inexpensive and, though obsolete, still readily available. The programmer for the board uses an FT232RL and the total cost is very low ([kodera2t] says it is in the price range of a Raspberry Pi Zero or about $4).

From a user’s point of view, a CPLD is just a small FPGA. Internally, there is a significant difference in how they implement your design. Although there are differences between different product families, CPLDs usually use a sea of logic gates arranged as an AND/OR chain. By feeding inputs and inverted inputs into the AND gates and then ORing the results, you can build interesting logic circuits. However, modern CPLDs use Verilog or VHDL, so you describe what you want just like with an FPGA and the software figures out how to use the underlying circuits to give you what you want.

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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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