Electronic – FPGA – DIY Programming

fpgaprogrammingspi

I've been programming microcontrollers for a few years now, and I've just discovered FPGA's after taking a digital design class. After doing some research into different FPGA's, development boards, etc, I'm still hesitant to buy any because I wouldn't know how to make my own version of the final "product." I've put PIC's, SAM's, AVR's, etc. on to custom PCB's with no issue, so I'm not worried about that–my main concern is programming an FPGA without a manufacturer's board.

My specific question: Would an FPGA function if I took the bitmap file generated by Quartus, Vivado, iCEcube, etc, wrote it to an SPI flash memory chip beginning at address 0 (say, via an FT2232H), and connected the flash memory to the SPI pins of an FPGA (with the MODE config set properly)?

I apologize for the partial hypothetical; I'm fairly sure that's all Lattice's Diamond Programmer does, but I wondered if that approach would work for FPGA's from different manufacturers, or whether say, Quartus added additional "window dressing" or headers to the memory while writing it.

Let me know if there's anything I can do to improve/clarify the question, or if I'm missing a big point in the FPGA programming process. Thanks!

Best Answer

Yes, it would work just fine.

Actually, the development tools for most FPGAs allow you to program the external flash directly through the FPGA's own JTAG connection, eliminating the need for a separate programming interface for the flash.

Start from scratch

Forget everything about software development. Especially programming languages. Those principles do not apply in digital design. It probably would be easy for a guy who designed a CPU to program it in assembler or even C, but an assembler programmer won't be able to design a CPU.

On your learning path do not tend to solve what seem to be an easy problem with your existing knowledge from software. One of the classic examples is a "for loop". Even though you can write a for loop in, say, verilog — it serves a different purposes. It is mainly used for code generation. It may also be a for loop as software developers see it, but it won't be good for anything but simulation (i.e. you won't be able to program FPGA like that).

So for every task you want to tackle, don't think you know how to do it, do a research instead — check books, examples, ask more experienced people etc.

Learn hardware and HDL language

The most popular HDL languages are Verilog and VHDL. There are also vendor-specific ones like AHDL (Altera HDL). Since those languages are used to describe hardware components, they are all pretty much used to express the same thing in a similar fashions but with a different syntax.

Some people recommend learning Verilog because it looks like C. Yes, its syntax is a mix of C and Ada but it doesn't make it easy for a software developer to lean. In fact, I think it may even make it worse because there will be a temptation to write C in Verilog. That's a good recipe for having a very bad time.

Having that in mind, I'd recommend staring from the VHDL. Though Verilog is also OK as long as the above is taken into account.

One important thing to keep in mind is that you must understand what you are expressing with that language. What kind of hardware is being "described" and how it works.

For that reason, I'd recommend you get yourself some book on electronics in general and a good book like this one — HDL Chip Design (aka as a blue book).

Get a simulator

Before you start doing anything in hardware and use any Vendor-specific features etc., get yourself a simulator. I was starting with a Verilog, and used Icarus Verilog along with GTK Wave. Those are free open-source projects. Run examples you see in books, practice by designing your own circuits to get some taste of it.

Get a development board

When you feel like going forward, get a development board. If you know that your employer wants to go with Lattice, then get Lattice board.

The programming methods are very similar, but there are details that are different. For example, different tools, different options, different interfaces. Usually, if you have experience with one vendor, it is not hard to switch. But you probably want to avoid this extra learning curve.

I'd also make sure that the board comes with components that you are planning to use or is extendable. For example, if you want to do design a network device like a router, make sure the board has Ethernet PHY or it can be extended through, say, HSMC connector, etc.

Boards usually come with a good reference, user guide and design examples. Study them.

Read books

You will need to read books. In my case, I had no friends who knew digital design, and this site wasn't very helpful either because of one simple thing — I didn't even know how to phrase my question. All I could come up with was like "Uhm, guys, there is a thing dcfifo and I heard something about clock domain crossing challenges, what is it and why my design doesn't work?".

I personally started with these:

Advanced Digital Design with the Verilog HDL.
100 Power Tips for FPGA Developers
Advanced FPGA Design - Architecture, Implementation and Optimization.

FPGA vendors have a lot of cookbooks with best practices. Study them along with reference designs. Here is one from Altera, for example.

Come back with more specific questions

While you go through your books, simulate a design, blink some LEDs on your development board, you would, most likely, have a lot of questions. Make sure you don't see an answer to those on the next page of the book or online (i.e. in the Lattice-specific forum) before asking them here.

Electronic – Custom FPGA PCB with external programming circuit

I think from your question you already understand this, but for clarification, this is my usual terminology:

Programming implies altering some non-volatile device
Configuration is what the FPGA does when it starts up - it loads its volatile internal memory from non-volatile external memory.

So, as you surmise, the system needs a non-volatile device of some sort which you program on the production line. To Clarify your comment on the USB blaster, it is not a chip... it's a "pod", so you'd have one for your programming station, not one per board:

USB blaster

Anyway, back to the non-volatile storage options:

The "Almost-zero-engineering required" approach uses Altera's configuration flash devices, which are JTAG programmable using something like a USB blaster. You just wire them up like the datasheet says, and away you go. They cost more per MBit than other options, though, so are not often used in volume production.
One more usual approach is a "normal" SPI flash chip. The Cyclone user guide configuration section will list some which are compatible with it, and I believe you can also use the Quartus software to program them via the JTAG of the FPGA they are connected to. More engineering involved, checking you have the right device etc. Also, if you are in volume production, you may not want to be using Quartus on the production line, which which case you may have to provide a separate programming header for the flash chip, and some hardware+software to drive that.
If you have a microcontroller in your system (even on another board...) you could connect that up to the FPGA's JTAG or configuration pins and store the FPGA bitstream in the micro's flash. More engineering involved as you have to have some software to "boot" the FPGA. however, it can make in-field upgrades easier, as often the micro is set up to receive software upgrades already, whereas updating the flash when it hangs directly off the FPGA is often an "opening the box" experience!