Visual6502 are peeling off the silicon from one of computer history’s benchmark chips, the MOS 6502, with acid and taking high-rez photos of it. Why? Because despite being only 35 years old, this chip is poorly understood.
To understand the 6502’s import, you have to understand that it powered the Apple I and Apple II, as well as the Atari and Nintendo game systems (and powering several famous robots). It contributed, in other words, to the birth of both personal computing and the development of the gaming industry.
Instead of creating an “emulator,” which is a not uncommon practice, this team instead created “a virtual chip by modeling and simulating the actual microscopic parts of a physical chip.” The problem with emulators is they rely on the documentation of an instruction set.
“This information is always incomplete and even the original chip logic schematics can differ from what was actually built in silicon. A disciplined emulator will capture and use traces of actual chip behavior, but it’s near impossible to capture the billions of sequences of bits that a real chip gives rise to…While a multitude of people understand the instruction set for the 6502, almost no one, apart from the original designers, understands how the physical chip achieves this instruction set.”
So they brought exposed the silicon die, took high-rez photos of its surface and substrate and, from these photos, created vector polygon models of each of the chip’s 20,0000 physical components.
“These components form circuits in a few simple ways according to how they contact each other, so by intersecting our polygons, we were able to create a complete digital model and transistor-level simulation of the chip.”
The Visual6502 site includes a JavaScript simulator of the chip, which is fun to play with regardless of your technical acumen. (Especially stepping the simulation forward with the n-key!) If your geekery happens to be high, the code for the chips is available on their GitHub page.
This isn’t their first rodeo. They’ve explored in detail other chips from the dawn of (computer) time, including the Intel 4004. But they’re hoping this process of digital archaeology – understand the physical makeup of chips, then building vector polygon models to test their play – will prove to be a more common tool going forward.
Additional sources: Techworld
