Interesting BiCMOS circuits in the Pentium, reverse-engineered

Intel released the powerful Pentium processor in 1993, establishing a long-running brand of processors. Earlier, I wrote about the ROM in the Pentium's floating point unit that holds constants such as π. In this post, I'll look at some interesting circuits associated with this ROM. In particular, the circuitry is implemented in BiCMOS, a process that combines bipolar transistors with standard CMOS logic.

The photo below shows the Pentium's thumbnail-sized silicon die under a microscope. I've labeled the main functional blocks; the floating point unit is in the lower right with the constant ROM highlighted at the bottom. The various parts of the floating point unit form horizontal stripes. Data...

Reverse-engineering a carry-lookahead adder in the Pentium

Addition is harder than you'd expect, at least for a computer. Computers use multiple types of adder circuits with different tradeoffs of size versus speed. In this article, I reverse-engineer an 8-bit adder in the Pentium's floating point unit. This adder turns out to be a carry-lookahead adder, in particular, a type known as "Kogge-Stone."1 In this article, I'll explain how a carry-lookahead adder works and I'll show how the Pentium implemented it. Warning: lots of Boolean logic ahead.

The die photo above shows the main functional units of the Pentium. The adder,...

It's time to abandon the cargo cult metaphor

https://invidious.privacyredirect.com/watch?v=iILq0ADHrw8

The cargo cult metaphor is commonly used by programmers. This metaphor was popularized by Richard Feynman's "cargo cult science" talk with a vivid description of South Seas cargo cults. However, this metaphor has three major problems. First, the pop-culture depiction of cargo cults is inaccurate and fictionalized, as I'll show. Second, the metaphor is overused and has contradictory meanings making it a lazy insult. Finally, cargo cults are portrayed as an amusing story of native misunderstanding but the background is much darker: cargo cults are a reaction to decades of oppression of Melanesian islanders and the destruction of their culture. For these reasons, the cargo cult metaphor is best...

January Update: Thinking Out Of The Vox

Happy New Year! This month we discuss the current state of the PineVox, seeing what the community have been up to with their PineNotes, announcing InfiniTime 1.15 and announcing the end of production of the Pinebook Pro.

Pi in the Pentium: reverse-engineering the constants in its floating-point unit

Intel released the powerful Pentium processor in 1993, establishing a long-running brand of high-performance processors.1 The Pentium includes a floating-point unit that can rapidly compute functions such as sines, cosines, logarithms, and exponentials. But how does the Pentium compute these functions? Earlier Intel chips used binary algorithms called CORDIC, but the Pentium switched to polynomials to approximate these transcendental functions much faster. The polynomials have carefully-optimized coefficients that are stored in a special ROM inside the chip's floating-point unit. Even though the Pentium is a complex chip with 3.1 million transistors, it is possible to see these transistors under a microscope and read out these constants. The...

Please refrain from installing WASP-OS on new PineTimes for the moment

In July 2024, PineStore notified the community that a small hardware change was needed on the PineTime: the current flash chip was end of life (EoL) and needed to be replaced by a new one. From the software point of view, the new chip behaves exactly like the old on so very few code changes were required to support it.

Free Stuff - September 2024

The belated September 2024 recipient for the Great Scott Gadgets Free Stuff Program is Allen Paschel of Orlando, Florida in the United States. Allen is the president of The Maker Effect Foundation which exists to inspire everyone to create! The Maker Effect Foundation is a non-profit organization that runs a maker space and teaches classes at schools, libraries, and events. The maker space has CNC machines, laser etcher/cutters, 3D Printers, vacuum forming equipment, welding tools, electronic tools, and other arts tools. Soon they will be able to add software-defined radio to that list of tools as we are sending them...

Free Stuff - August 2024

The belated August 2024 recipient for the Great Scott Gadgets Free Stuff Program is Murat Sever! Murat teaches a Communication Systems Laboratory course at TOBB ETU University, Ankara, Turkey. In his labs, Murat uses two HackRFs to transmit signals of interest, which students receive via RTL-SDRs. Murat has requested an Opera Cake so his students can study Pseudo Doppler direction finding and to teach students about antenna switching and spectrum monitoring. For more information about Murat’s course, his and his students’ research projects, and their outreach programs, please check out their website (https://ele361l.github.io/).

This application for the Free Stuff program stood...

Free Stuff - July 2024

The belated July 2024 recipient for the Great Scott Gadgets Free Stuff Program is Scott Carter from Ontario, Canada! Scott operates a SETI station that uses a radio telescope he built using software defined radio. He says the radio telescope has been in operation for six and a half years, and it needs a receiver upgrade to allow scanning of frequencies above 2 GHz. We are sending Scott a HackRF One so he can make his radio telescope upgrade! Scott’s long-term goal is to make his SETI station accessible remotely for educational purposes so more folks can learn about radio...

Free Stuff - June 2024

The belated June 2024 recipient for the Great Scott Gadgets Free Stuff Program is Evan Metzinger. Evan is the president of the Cybersecurity club at Mt. San Antonio college in Walnut, California in the US. We will be sending Evan a HackRF One so he and his club can get some hands on experience with signals processing and participate in wireless capture the flag competitions.