Turtles all the way down: Integrated circuits

The next phase of the trusted open computer project is actually manufacturing usable integrated circuits that you can plug into a circuit board, apply power to, and use to do whatever it is that you do. In other words, processing information. I hate to be a killjoy, but this is really hard. A vital question that we have to ask at this point is whether or not this is the point at which the project is pwnable by a determined third party. Fabbing integrated circuitry on silicon wafers is, to be gentle, a nontrivial process. Here are a couple of links on how the process can go:

• https://en.wikipedia.org/wiki/Semiconductor_device_fabrication
• http://rel.intersil.com/docs/lexicon/manufacture.html
• http://www.ti.com/corp/docs/manufacturing/howchipmade.shtml
• http://www.eecg.toronto.edu/~vaughn/wafer.html

Even Jeri Ellsworth, who is somebody for whom I have the utmost of admiration and respect, spent two years building a semiconductor foundry in her home and as far as I know (and I'd love to hear different) she's only up to fabbing her own discrete transistors. I think says something for how far we are from fabbing our own ICs at home. In case you're curious here's her photo album for her home semiconductor fab. It's a breakthrough, to be sure, and I have no doubt that she will one day fabricate her own CMOS and NMOS chips. However I think that day is a considerable period of time in the future and, for the purpose of practically implementing a computer system from the ground up, doing so is not an option yet. But what can we do that will get us results? A more commonly used method of implementing custom chips is compiling the design into an FPGA (field programmable gate array), which is a chip that you can load code into to turn it into whatever you want, like a CPU, a math coprocessor, a communications controller, a graphics comtroller, or something more unusual (like a signal processor). The nature of FPGAs is that they are slower than fabbed chips (but they're getting better, and some high-end Xilinx FPGAs run at speeds practically indistinguishable from ASICs) but if you don't have your own chip foundry they're probably the only realistic option open unless you feel up to the task of building functional versions of the ICs out of discrete components. Which you can do, as the following examples depict:

• http://www.evilmadscientist.com/2013/555-kit/
• http://www.retroclinic.com/leopardcats/bbpokey/breadboard_pokey_project.htm
• MT15 transistorized CPU
• A gallery of various homemade CPUs

By their very nature they'll be orders of magnetude larger than the originals and will probably have unusual quirks due to the constraints of macroscale electrical engineering. So, if you're the sort of person who is not willing to sacrifice some speed just to have a working system, you're out of luck at this point. FPGAs also notably differ in the number of logic gates they are constructed out of. Some have enough hardware on board - microprocessors, clocks, and other stuff - that they can be used to fabricate full Systems-On-A-Chip, which I'll talk about later. Some designs may require FPGAs of a minimum number of gates, speed, or other onboard functionality so a hacker would have to be mindful of the specifications of the FPGAs acquired and match them to their intended purpose. Additionally, the un-flashable onboard subsystems of some FPGAs may be subvertable somewhere along the supply line, certainly at the factory but possibly closer to home. I don't feel comfortable speculating any farther beyond that due to my comparative lack of hands-on knowledge of FPGA technology. Then there is the argument of open source versus closed source FPGA synthesis and programming software. The few times I've mentioned using FPGAs to construct computers while doing research for this article the discussion rapidly turned into a debate over the ethics of using closed source software to build open source integrated circuitry. I'm not going to restart that debate, ple