μblog: engineering from the trenches

This weeks entry is a 48-LQFP chip labeled Msi M5-46266 that came off a Pentium4 mainboard. Looking at the die, it can be seen that this is actually Winbond chip. The part number doesn’t match up on their site, however, the large driving circuitry on the pins makes me guess that it is some kind of host controller or a clock generator.

msi46266-10x-stitch.jpg

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While looking for ways to escape muti-variate calculus purgatory in the final weeks of the semester, I came across Open Math Text.  These are a collection of math books (in PDF and LaTeX) that are openly available for distribution and are aimed at general scholars. A quick look at the collection will show that most of the books are authored by Dr. David Santos, a professor a the Community College of Philadelphia.  It seems that he has written and made available more books, in multiple languages, than the number of scholarly papers that most researchers publish at full universities.

While looking at his personal page, I found another open textbook collection called Textbook Revolution. The obvious downside is that these publications may not go through the same levels of review as textbooks printed at conventional publishers, however, it is nice to know that there is a group of people actively working to make affordable textbooks available.

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As I have mentioned, the semester is winding down and projects are piling up. To help move things along, I have written a pair of documents that outline how to determine the conductivity of a plane (and volume) with a conducting disk (and sphere) of arbitrary size in the middle. I solved Laplace’s equations in both polar and spherical coordinate systems, then used boundary conditions to determine the electric potential and then determined the ratio of applied field to current density to determine the conductivity in the presence of the suspended object. I have checked these early drafts over a few times, however, there may still be some mistakes remaining, so please be warned. Also, feel free to post questions and I will make an attempt to answer them.

( disk-efield.pdf )

( sphere-efield.pdf )

P.S. The photo-op was staged during my last vacation, I would never use Classical Electrodynamics as a coaster.

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This weeks entry is a mystery chip from Sony that was found in a Playstation2. The image above displays the only markings.

7061-4x-stitch.jpg

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Whenever I get a shiny new copy of Electronic Design magazine, I eagerly read the section called Pease Porridge, at the very end of the magazine. This section is written by Bob Pease and typically contains whatever material Mr. Pease decides to include that month. In my view, this is the only page in the magazine that actually includes electronic designs and is in contrast with the rest of the magazine’s content (advertisements that look like written text).  Sometimes there are designs for circuits that detect dropping temperatures in boots, sometimes something on taxes, and sometimes the section contains responses to letter (or emails) that readers have sent in. This month’s porridge dealt with sent in letters and the first one, by Anonymous Engineer, has provoked some thought.

Hello Bob,

A note concerning electric cars and plugin hybrids: Consider that politics has little to do with engineering and/or science. It only pays lip service at those altars. So, somebody has to do serious planning for the immediate future.

I’ve been working on some serious battery-charger designs. One of our planners (an engineer) did some research in good old California. We learned that your utility companies have problems with metering even small numbers of plug-ins, nor can the California infrastructure absorb many cells of even 5000 plug-ins. You’re running at about 81% capacity, and without a smart meter and control, we would easily overload the electricity capacity on two peaks every day. That’s not politics. It’s business.

American, Japanese, and European manufacturers were contacted, and none of us can really do this without the cooperation of the utilities. Oh sure, we can sell a few and look green. The press wouldn’t even know who to blame when the grid broke. Some of our competitors have been doing that, but without that smart meter, it’s the wrong thing to do. They know it. But that’s business.

All of the automakers easily agreed on the meter and protocol. The utilities did not. They already have contracts on meters that aren’t smart. That’s business. The real greenies were there, too. They’re part of politics. They want California to be energy neutral in 10 years—sorry, no data on how to do it. Industry must be hiding it.

Back in the Midwest, we run about 1/2 the total power per person aggregate (at 740 W per person continuous) than you do out west, but that’s because of our low transport and air conditioning costs. Perhaps just targeting our levels would be a better starting point. There is no magic bullet in the next 10 years. So the utilities answer to the greenies and business, not to the engineers. Our charger is going to be great. We will get patents. It will be used all over, but not in volume in the west.

-An Anonymous Engineer

Prior to reading this, I have been all for plug-in electric vehicles, although I have never worked out the power load requirements to support such a population. Now thinking a of the power blackouts that crippled the North-Eastern United States a few years back, I am no longer sure that switching privately owned vehicles to plug-ins is the right thing to do right now due to obvious issues with the power infrastructure in the U.S. Although the need to address environmental issues related to automobiles is apparent, I doubt there will be a serious motivation behind it unless there are economic benefits involved. The switch over to electric (or hydrogen for that matter) vehicles should start with the sector that can be converted most efficiently which would allow for the highest return on investment.

In my mind, the public transportation system should make the switch first. I am mostly experienced with the Metro fleet in Washington D.C. and can note that all of the buses are made by Orion Bus Industries (owned by Daimler Trucking) and fall into two models (larger and smaller). Given that the buses operate on a pre-determined route and are equipped with GPS (to automate the current location display inside the bus), the energy demand per vehicle per day can be predicted with high accuracy. Furthermore, most of the vehicles are at the depot during the late night and early morning, when electricity is cheaper than the daytime, which would make for an ideal charging period.

Over all, this would lead to a very predictable off-peak energy demand that can be negotiated with the local power generation utility in advance to ensure that the power demand is met economically and without sacrificing the power grid’s integrity. An on-site generator may be employed to charge batteries in case of a power emergency where public transportation service is required. A more clever (and more difficult) design may involve modifying the buses to have a modular power system that can be swapped between conventional diesel and electric power-plants.

Again, most of this is mostly my intuition as I have not worked out most of the mathematics behind it, however, it seems that power demand predictability might be a mitigating economic factor for public transportation conversion. Unlike us, the bus driver rarely gets sleepy while reading at night and takes the bus out for a spin to the coffee shop.

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The semester is winding down, which means there are a lot of deadlines piling up. One of my deadlines involves re-deriving some work by Hugo Fricke regarding the electrical properties of suspensions of conducting spheres in a conducting medium. Fricke was one of the pioneers of radio-therapy and was one of the first individuals to postulate that blood cells had membranes (instead of being homogeneous solids). He did this through electrical interrogation of blood alone without using any optical techniques. I am posting my step-by-step derivations for the electric potential inside and around a single conducting sphere in a conducting medium with regards to electrostatics. I solve Laplace’s equation using separation of variables in a spherical coordinate system. Hopefully I didn’t make many errors and the rest of the derivation relating total cell conductivity and capacity will follow.

( sphere-efield.pdf ) (Image is from GNU)

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Since I have started the IC Friday weekly section, I have accumulated a significant number of exposed dies. In a general effort to reduce clutter, I would like to give these away as it is unlikely that I will refer to the dies in the future. The 70 or so dies will be split into two categories, digital and analog, and each will be mailed to a random commenter using the US Postal Service. If you are interested, leave a comment below indicating your preference for digital or analog dies. Please use a valid email address when making the reply, I will need it to contact you and it will not be displayed to the public. I will keep this open for two weeks and will let MATLAB (2008a) decide the winners on May 9th. Good luck and feel free to post any questions.

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For almost every digital circuit designer out there signal integrity problems often come up as frequencies increase, board sizes decrease and IC pin impedances change. (Every designer except for myself, I work with very low frequency analog circuits!) When signal integrity becomes so poor that unacceptable levels of transmission errors are reached, the efficient digital designer may venture into the analog domain and start looking at transmission line models of their digital traces. For those who prefer to think of everything as analog, this could be the point of argument to “prove” that ones and zeros only exist in the digital designer’s mind and do not represent physical reality (although thinking of voltages as high/low is sometimes more efficient).

Sometime in the 1970s, Motorola introduced digital emitter coupled logic (M ECL) circuits. I don’t know if Motorola was first, however, they had plenty of expertise on the subject. The made ECL useful in those days was the incredibly fast switching rate for these types of logic circuits. ECL works very similarly to standard bi-polar junction transistor based designs, however, the transistors in ECL are always partially conducting. The high and low logic levels are determined by different points along the devices’ load curves which made them faster than BJT devices which had to go from completely off to completely on to switch logic. ECL devices were (and still are) much faster than comparable CMOS devices since CMOS depends on relatively slow thermal generation of carriers to create the conduction region. The point is that fast digital circuits are not that new, and we are facing some of the same transmission line problems as thirty years ago when we scale dimensions and voltages down and increase the operating frequency. If the operating frequencies of interest are such that wave lengths (in the conducting metal trace) are comparable to the length of the trace, transmission line models must be employed. This matter of wavelength can be a tricky question to answer as it can be readily shown that the wavelength of a 60Hz signal in a thick copper conductor is about 5cm (with a phase velocity of only 3.22m/s).

Now that we believe that our traces can act like transmission lines, we are faced with a problem of matching impedance. In the simplest of cases, we have only the driving logic (generator), the trace and the receiving logic (termination). From a driving perspective, the output impedance of the device should closely match the trace impedance, typically something like 30-70Ohms. If the output logic is not matched to the trace, a reflection will not occur at the driving logic in the strict sense, however, the signal traveling down the conducting trace will already be deformed. Now that we have a packet of current traveling down the trace, as specified by the generator, any mismatch in impedance between the trace the termination logic will result in a reflection which will further deform the other current packets traveling down the conductor. This problem can easily happen when CMOS logic (infinite input impedance) is coupled with low output impedance logic and the transmission frequency is gradually increased. The problem becomes more complicated when there are multiple terminations on a given conductor segment as each impedance mismatch generates a reflection and so forth.

Besides the MECL Design Handbook,  Altera provides a few application notes [1][2][3] on signal integrity and high speed design which include termination practices. Typically, introducing a resistor in series or in parallel (to ground) is all that is required to mostly match impedances and give adequate performance, the most important concept is knowing when and where to use these terminating resistors. Although some devices come with various termination options built into the die, most still don’t, so it is good to know when a properly placed resistor network can save a lot of shielding attempts and speed up the debugging process.

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Over a decade ago, I remember printing out and reading a text by Aleph1 entitled Smashing the Stack for Fun and Profit. Back then, stack-based buffer overflows were a hot topic and the tide was turning as programmers began to realize that null termination of strings was not a good security measure and bounds checking was becoming necessary for the security-minded programs.

The issue was that many people were used to using a function like strcpy() to copy a string from one memory location to a dynamically allocated memory segment on the stack. The strcpy() function simply started copying from the supplied address and stopped when it reached a null character without knowing how much space was allocated for the string at the destination. As a result, segments of the stack that were not allocated for the “local” variable, like the return address of a function, could be overwritten with arbitrary values. With the properly formatted string, even executable code could be put somewhere on the stack and the return address could be overwritten so that this code could be executed, for fun and profit as they say. Programmers became wiser and started using strncpy() instead, which only copied a fixed amount of data and therefore guaranteed that the allocated space would not be exceeded. Furthermore, most modern operating systems can now set areas of the memory dedicated to the stack as non-executable, so the above routine would be foiled. Individuals have found some ways around these security features, however, the stack smashing exploit (as described by Aleph1) has mostly been considered a thing of the past.

I use the term mostly since Nintendo has preserved the knowledge and allowed practice of this exploit with their release of the latest Zelda game for the Wii. Through a cleverly crafted save file, the name of the main characters horse can contain a string as mentioned above and lead to execution of arbitrary code. There are a few tricks to maintain the integrity of the save file, however, after a decade the above exploit still lives on, almost in the same form as described by Aleph1.

( Although the picture is not from the Twilight Princess game, it is a good game none the less. )

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Today, we are presented with the venerable i386 processor which kicked off the 32bit era for the x86 architecture. This one happens to have a math-coprocessor on board as well.

i386-4x-stitch.jpg

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