The 386's main register bank, at the bottom of the datapath. The numbers show how many bits of the register can be accessed. (Credit: Ken Shirriff)

The Convoluted Way Intel’s 386 Implemented Its Registers

May 5, 2025 by Maya Posch 4 Comments

The fact that modern-day x86 processors still pretty much support the same operating systems and software as their ancestors did is quite a feat. Much of this effort had already been accomplished with the release of the 80386 (later 386) CPU in 1985, which was not only the first 32-bit x86 CPU, but was also backwards compatible with 8- and 16-bit software dating back to the 1970s. Making this work transparently was anything but straightforward, as [Ken Shirriff]’s recent analysis of the 80386’s main register file shows.

Labelled Intel 80386 die shot. (Credit: Ken Shirriff)

Using die shots of the 386’s registers and surrounding silicon, it’s possible to piece together how backwards compatibility was implemented. The storage cells of the registers are implemented using static memory (SRAM) as is typical, with much of the register file triple-ported (two read, one write).

Most interestingly is the presence of different circuits (6) to support accessing the register file for 8-, 16- or 32-bit writes and reads. The ‘shuffle’ network as [Ken] calls it is responsible for handling these distinct writes and reads, which also leads to the finding that the bottom 16 bits in the registers are actually interleaved to make this process work smoother.

Fortunately for Intel (and AMD) engineers, this feat wouldn’t have to be repeated again with the arrival of AMD64 and x86_64 many years later, when the 386’s mere 275,000 transistors on a 1 µm process would already be ancient history.

Want to dive even deeper in to the 386? This isn’t the first time [Ken] has looked at the iconic chip.

Testing A Cheap Bench Power Supply Sold On Amazon

May 3, 2025 by Maya Posch 20 Comments

We’ve all seen those cheap bench power supply units (PSUs) for sale online, promising specifications that would cost at least a hundred dollars or more if it were a name brand model. Just how much of a compromise are these (usually rebranded) PSUs, and should you trust them with your electronics? Recently [Denki Otaku] purchased a cheap unit off Amazon Japan for a closer look, and found it to be rather lacking.

Internals of the cheap bench PSU reviewed by Denki Otaku on YouTube.

Major compromises include the lack of an output power switch, no way to check the set current limit without shorting the output, very slow drop in output voltage while adjusting due to the lack of a discharge circuit, and other usability concerns. That’s when the electrical performance of the PSU got tested.

Right off the bat a major issue in this cheap switching mode PSU is clear, as it has 200 mV peak-to-peak noise on its output, meaning very little output filtering. The maximum power output rating was also far too optimistic, with a large voltage drop observed. Despite this, it generally worked well, and the internals – with a big aluminium plate as heatsink – look pretty clean with an interesting architecture.

The general advice is to get a bench PSU that has features like an output power button and an easy way to set the voltage and current limits. Also do not connect it to anything that cares about noise and ripple unless you know that it produces clean, filtered output voltages.

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Neutron Flux Impact On Quartz Expansion Rate

April 30, 2025 by Maya Posch 8 Comments

Radiation-induced volumetric expansion (RIVE) is a concern for any concrete structures that are exposed to neutron flux and other types of radiation that affect crystalline structures within the aggregate. For research facilities and (commercial) nuclear reactors, RIVE is generally considered to be one of the factors that sets a limit on the lifespan of these structures through the cracking that occurs as for example quartz within the concrete undergoes temporary amorphization with a corresponding volume increase. The significance of RIVE within the context of a nuclear power plant is however still poorly studied.

A recent study by [Ippei Maruyama] et al. as published in the Journal of Nuclear Materials placed material samples in the LVR-15 research reactor in the Czech Republic to expose them to an equivalent neutron flux. What their results show is that at the neutron flux levels that are expected at the biological shield of a nuclear power plant, the healing effect from recrystallization is highly likely to outweigh the damaging effects of amorphization, ergo preventing RIVE damage.

This study follows earlier research on the topic at the University of Tokyo by [Kenta Murakami] et al., as well as by Chinese researchers, as in e.g. [Weiping Zhang] et al. in Nuclear Engineering and Technology. [Murayama] et al. recommend that for validation of these findings concrete samples from decommissioned nuclear plants are to be examined for signs of RIVE.

Heading image: SEM-EDS images of the pristine (left) and the irradiated (right) MC sample. (Credit: I. Murayama et al, 2022)

A Gentle Introduction To COBOL

April 30, 2025 by Maya Posch 70 Comments

As the Common Business Oriented Language, COBOL has a long and storied history. To this day it’s quite literally the financial bedrock for banks, businesses and financial institutions, running largely unnoticed by the world on mainframes and similar high-reliability computer systems. That said, as a domain-specific language targeting boring business things it doesn’t quite get the attention or hype as general purpose programming or scripting languages. Its main characteristic in the public eye appears be that it’s ‘boring’.

Despite this, COBOL is a very effective language for writing data transactions, report generating and related tasks. Due to its narrow focus on business applications, it gets one started with very little fuss, is highly self-documenting, while providing native support for decimal calculations, and a range of I/O access and database types, even with mere files. Since version 2002 COBOL underwent a number of modernizations, such as free-form code, object-oriented programming and more.

Without further ado, let’s fetch an open-source COBOL toolchain and run it through its paces with a light COBOL tutorial.

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Building An NRF52840 And Battery-Powered Zigbee Gate Sensor

April 30, 2025 by Maya Posch 23 Comments

Recently [Glen Akins] reported on Bluesky that the Zigbee-based sensor he had made for his garden’s rear gate was still going strong after a Summer and Winter on the original 2450 lithium coin cell. The construction plans and design for the unit are detailed in a blog post. At the core is the MS88SF2 SoM by Minew, which features a Nordic Semiconductor nRF52840 SoC that provides the Zigbee RF feature as well as the usual MCU shenanigans.

Previously [Glen] had created a similar system that featured buttons to turn the garden lights on or off, as nobody likes stumbling blindly through a dark garden after returning home. Rather than having to fumble around for a button, the system should detect when said rear gate is opened. This would send a notification to [Glen]’s phone as well as activate the garden lights if it’s dark outside.

Although using a reed relay switch seemed like an obvious solution to replace the buttons, holding it closed turned out to require too much power. After looking at a few commercial examples, he settled for a Hall effect sensor solution with the Ti DRV5032FB in a TO-92 package.

Whereas the average person would just have put in a PIR sensor-based solution, this Zigbee solution does come with a lot more smart home creds, and does not require fumbling around with a smartphone or yelling at a voice assistant to turn the garden lights on.

Comparing ‘AI’ For Basic Plant Care With Human Brown Thumbs

April 29, 2025 by Maya Posch 18 Comments

The future of healthy indoor plants, courtesy of AI. (Credit: [Liam])

Like so many of us, [Liam] has a big problem. Whether it’s the curse of Brown Thumbs or something else, those darn houseplants just keep dying despite guides always telling you how incredibly easy it is to keep them from wilting with a modicum of care each day, even without opting for succulents or cactuses. In a fit of despair [Liam] decided to pin his hopes on what we have come to accept as the Savior of Humankind, namely ‘AI’, which can stand for a lot of things, but it’s definitely really smart and can even generate pretty pictures, which is something that the average human can not. Hence it’s time to let an LLM do all the smart plant caring stuff with ‘PlantMom’.

Since LLMs so far don’t come with physical appendages by default, some hardware had to be plugged together to measure parameters like light, temperature and soil moisture. Add to this a grow light and a water pump and all that remained was to tell the LMM using an extensive prompt, containing Python code, what it should do (keep the the plant alive), and what Python methods are available. All that was left now was to let the Google’s Gemma 3 handle it.

To say that this resulted in a dramatic failure along with what reads like an emotional breakdown on the part of the LLM would be an understatement. The LLM insisted on turning the grow light on when it should be off and had the most erratic watering responses imaginable based on absolutely incorrect interpretations of the ADC data, flipping dry and wet. After this episode the poor chili plant’s soil was absolutely saturated and is still trying to dry out, while the ongoing LLM experiment, with an empty water tank, has the grow light blasting more often than a weed farm.

So far it seems like that the humble state machine’s job is still safe from being taken over by ‘AI’, and not even brown thumb folk can kill plants this efficiently.

ASUS GPU Uses Gyroscope To Warn For Sagging Cards

April 28, 2025 by Maya Posch 51 Comments

It’s not really an understatement to say that over the years videocards (GPUs) — much like CPU coolers — have become rather chonky. Unfortunately, the PCIe slots they plug into were never designed with multi-kilogram cards in mind. All this extra weight is of course happily affected by gravity.

The problem has gotten to the point that the ASUS ROG Astral RTX 5090 card added a Bosch Sensortec BMI323 inertial measurement unit (IMU) to provide an accelerometer and angular rate (gyroscope) measurements, as reported by [Uniko’s Hardware] (in Chinese, see English [Videocardz] article).

There are so-called anti-sag brackets that provide structural support to the top of the GPU where it isn’t normally secured. But since this card weighs in at over 6 pounds (3 kilograms) for the air cooled model, it appears the bracket wasn’t enough, and active monitoring was necessary.

The software allows you to set a sag angle at which you receive a notification, which would presumably either allow you to turn off the system and readjust the GPU, or be forewarned when it is about to rip itself loose from the PCIe slot and crash to the bottom of the case.