Silego’s GreenPAK – Design and program a custom chip in minutes

When I was a young lad just starting to play with electronics in the early 1970s, most of my designs were digital. These little scamps were based on the use of 74-series TTL “Jelly Bean” devices, so even a relatively simple design typically required a whole bunch of chips and a relatively large circuit board.

I used to read a lot of science fiction in those days (I still do, of course). I remember thinking that one day it might be possible to have something the size of a large photocopier or chest freezer that could create custom integrated circuits to one’s specification. I wasn’t entirely sure how this would work – just that there would be some way for you to capture a circuit diagram and then you’d press the “Big Red Button” and there would be some impressive light and sound effects and out would pop your new chip.

I know that things are moving incredibly quickly these days technology-wise, but even so I would never have guessed that I would one day be sitting at my desk with the ability to design and implement a custom chip within a few minutes. Believe it or not, however, this is the case…

Introducing Silego’s GreenPAK 1
While I was at DAC 2011, I met up with Aron Cooperman from Silego Technology (www.silego.com). Silego make a variety of electronic products (GreenFET, GreenCLK, GreenDDR3, etc.), but the one that’s of the most interest to me is their GreenPAK 1, which comes in the form of an 8-pin 2mm x 2mm surface mount package.


Obviously this looks rather “beefy” in this image, but if you draw a 2mm x 2mm square on a piece of paper you’ll realize just how small this is, and yet this little beauty packs a lot of “wallop” as we shall see.

The way I think of the GreenPAK 1 is as a super-small mixed-signal FPGA that you can design and program in just a few minutes and that costs only a few cents (more on this below). A brief summary of the GreenPAK 1’s features is as follows:

• Operating voltage = 3.3V
• Eight Pins
• One 8-bit SAR analog-to-digital converter (ADC)
• Two analog/digital comparators
• One internal voltage reference
• Seven look-up tables (LUTs) (2 x 2-bit, 4 x 3-bit, 1 x 4-bit)
• Three flip-flops / latches
• One pulse width modulator (PWM)
• One internal oscillator

Out of the 8 pins, one is power and one is ground, which leaves 6 pins that the user can configure as inputs or outputs. Also either pin 6 or pin 7 can be configured to act as the analog input to the ADC and/or the analog/digital comparators (both pins will be used if you decide to employ a differential signal).

Just to provide a really simple example, consider a chunk of digital glue logic on a circuit board:

This would typically require five individual chips, which consume board real estate, increase the size, cost, weight, and power consumption of the design, and also negatively impact the product’s reliability because every solder joint is a potential cause for failure. By comparison, the same design would easily fit in a single GreenPAK 1 chip:

Aron says that, in a typical usage scenario, a GreenPAK 1 will replace 10 to 15 components, but that one of Silego’s customers actually managed to replace 36 components, which is pretty significant whichever way you look at it.

Interesting nuggets of knowledge
In a moment we’re going to talk about the process of actually capturing and implementing a design using a GreenPAK 1 chip, but before we do so my head is full of all sorts of nuggets of knowledge and tidbits of trivia that I have to write down before my noggin explodes, so here we go…

Design Capture: You can capture your design using the free software tools (including multiple reference designs) that are available from the Silego website (www.silego.com). Alternatively, you can use Silego’s in-house application team to capture and verify your design, which may take anything from a couple of hours to a couple of days depending on your design’s complexity and also how articulate you are (that is, how good you are at explaining what you want to do). Aron says that some of their customers simply send in schematic diagrams sketched out on cocktail napkins; others provide a text description or explain what they want over the phone.

Design verification: If you are capturing the design yourself using Silego’s free software tools, you can verify the design using the GreenPAK 1 emulation board as discussed later in this paper. This evaluation board is an absolute bargain at only $75, not the least that it comes with 50 unprogrammed chips for you to play with. (I have one of these little rapscallions on my desk and it is wonderful!)

Obtaining Physical Chips: If you are using the emulation board discussed above, then you will have your first chips as soon as you program them (remember the board comes with 50 unprogrammed chips). When it comes to obtaining production devices, you have two choices: One-Time Programmable (OTP) or mask programmed. Assuming you capture and verify your design yourself using the free software tools and the emulation board discussed above, then once you email your design to Silego, they can return fully characterized data sheet and start bulk supplying your new parts in 72 hours or less. Alternatively, if you opt for the mask-programmed option, this will take about two weeks before you start to see your production chips.

Design Security: GreenPAK 1 chips are delivered in packages with non-traditional markings, so if anyone looks at the circuit board there is no way for them to tell what these chip are or what they do.

Low Power: A GreenPAK 1 chip can consume as little as 20 nA (nanoamps) assuming a purely digital logic design. Alternatively, with everything running at absolutely full throttle (PWM, ADC, Oscillator, etc.), the power consumption will top out at around 400 uA (microamps).

Low Cost: You’ll have to talk to the folks at Silego about this, but my understanding is that you can get programmed GreenPAK 1 devices for 15 cents each when purchasing in ultra-high volumes

Why the name GreenPAK? One reason is that these components allow designers to create smaller, more ecologically-friendly circuit boards that require fewer chips and consume less power. Another is that they allow designers to quickly and easily “cleanup” their designs (grin).

Silego – the Company: Apparently Silego has been around for about ten years and has approximately 100 employees (the majority of whom are in Silicon Valley, California). In the case of their GreenPAK 1 product, they’ve shipped 85+ million production units in the last year and a half, and this number is starting to ramp up exponentially as more and more designers discover this technology.

Capturing and verifying a design
This is just so amazingly cool – I love it. Let’s assume that you’ve already sketched out a schematic on a piece of paper (the way we used to do things in the good old days when I was a lad). In this case, your next step is to use the GreenPAK Designer application (available free from the Silego website).


This really is intuitive to use (not the least that it comes equipped with tutorials and a bunch of reference examples at your fingertips). On the right-hand side of the interface are the functional components that are available to you in the GreenPAK chip (LUTs, registers, analog comparators, digital comparators, ADC, PWM, etc.). You can disable any functions you don’t require by toggling the checkbox next to them (disabled functions disappear from the screen and they won’t consume any power in the physical device).

You can quickly and easily connect wires from primary inputs to component inputs, component outputs to component inputs, and component outputs to primary outputs. Clicking a register element brings up a dialog that allows you to select whether this is to act as a flip-flop or a latch. Clicking a LUT brings up a dialog that allows you to configure it using a truth-table format. Clicking a pin allows you to specify its type (digital, analog, etc.) and attributes (pull-up, pull-down, resistance value, etc.).  And so it goes…

The next tool is the emulator board, which (as I mentioned before) comes equipped with 50 unprogrammed devices and (in my humble opinion) is a real bargain at only $75.


Observe the little daughter card with the plastic socket on top. This has been unplugged here to better illustrate what we’re talking about, but it would typically be plugged into the connector in the middle of the main emulation board. Now, remember that we’re dealing with a chip 2mm x 2mm with 8 pins, so when you are designing a new chip you obviously don’t want to be trying to solder it onto the board by hand; instead you pop open the socket, into which you place your chip. When you close the socket, it automatically aligns the chip and makes good connections.

The next step is to connect the emulation board to your computer using the supplied USB cable, and then you download your configuration from GreenPAK Designer into the GreenPAK Emulator. All of this is controlled by the GreenPAK Emulator application, which runs on your computer.


One thing I didn’t understand when Aron was first demonstrating all of this to me was how it was that he managed to keep on reprogramming the same GreenPAK device to do different things [you will recall that the devices supplied with the emulation board are One-Time Programmable (OTP)]. I later discovered that the GreenPAK chip contains two sets of configuration cells; each of the OTP cells has a corresponding low-power SRAM equivalent.

When a GreenPAK chip is being used on a real circuit board, upon power-up the contents of the OTP cells are automatically copied into their SRAM equivalents, and it’s these SRAM cells that are used to control the device. Alternatively, when the GreenPAK chip is being used in conjunction with the emulation board, you can verify and refine your design by simply loading your configuration into the SRAM cells and changing the configuration as you desire. Later, when you are finally ready to rock-and-roll, you can program your configuration into the OTP cells, after which you can pop the chip out of the emulator and onto your real (or prototype) board.

There’s so much more to all of this. For example, there’s a Signal Wizard that allows you to specify stimulus to drive whichever pins you program as inputs on the Emulator Board using digital logic signals or more sophisticated “saw tooth” and similar waveforms as shown below:



You can also use the Signal Wizard to apply common analog signals like Sine and Cosine waves. And you can even create fully custom waveform envelopes as shown below:


One slight “gotcha” is that you can’t capture and display the outputs from the GreenPAK Emulation board on your PC. On the one hand I think that this is little unfortunate, but I’m sure they have their reasons (like keeping down the price and complexity).

So how do you analyze the results from the Emulator? Well, each of the I/O pins on the GreenPAK Emulator board has an associated “hook” to which you can attach an oscilloscope or logic analyzer probe. Of course this immediately reminded me of that very cool iPad-iPhone-iPod-based oscilloscope from Oscium that I looked at a couple of months ago.

At that time I didn’t have an iPad, so I returned the little scamp to its creators. As you may recall, however, I subsequently became the proud owner of an iPad … so now I have an iPad but no oscilloscope for it (“A thousand curses,” I cry! [grin]). Oh well, who knows what tomorrow may bring…

Summary
So there you have it. I personally think that the folks at Silego have come up with something very clever and very useful with regard to their GreenPAK 1 technology. In fact, off the top of my head I can’t think of anything that’s equivalent to this and I really cannot wait to see what they come up with next…

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