David Chisnall (*Now with 50% more sarcasm!*)

@david_chisnall@infosec.exchange
2.6K Followers
83 Following
6.6K Posts

I am Director of System Architecture at SCI Semiconductor and a Visiting Researcher at the University of Cambridge Computer Laboratory. I remain actively involved in the #CHERI project, where I led the early language / compiler strand of the research, and am the maintainer of the #CHERIoT Platform.

I was on the FreeBSD Core Team for two terms, have been an LLVM developer since 2008, am the author of the GNUstep Objective-C runtime (libobjc2 and associated clang support), and am responsible for libcxxrt and the BSD-licensed device tree compiler.

Opinions expressed by me are not necessarily opinions. In all probability they are random ramblings and should be ignored. Failure to ignore may result in severe boredom and / or confusion. Shake well before opening. Keep refrigerated.

Warning: May contain greater than the recommended daily allowance of sarcasm.

No license, implied or explicit, is granted to use any of my posts for training AI models.

So the UK Met Office is inviting people to suggest up to 5 names for storms. And apparently lots of people have been suggesting "Storm Bigoil", along with BP, Equinor, Exxon & Shell... This is obviously appalling & definitely not to be emulated via this link:

https://www.metoffice.gov.uk/forms/name-our-storms-call-for-names

@jmc It's kind of impressive in its glorious insanity.

I just re-read Don's "X Windows" chapter of the Unix Haters Handbook for the first time since probably nineteen diggity-aught -- http://www.art.net/~hopkins/Don/unix-haters/x-windows/disaster.html

....and like 80% of it still tracks if you s/X/Wayland/

The Iran-Contra jokes in there kinda hit different today, and yet also don't, at all.

Time is a flat circle.

The X-Windows Disaster

I have done all the braining I can do. No more brain until tomorrow.

Ive just found a wallet with $20 in it.

I wasnt sure how to proceed, but then I thought, What would Jesus do?

So I turned it into wine.

The wealth of the world’s 3,000 billionaires has surged by $6.5tn (£4.8tn) in real terms over the past decade, according to Oxfam, equivalent to 14.6% of global output.

In total the richest 1% of the global population has gained at least $33.9tn in real terms, which the charity said was “enough to end annual global poverty 22 times over”.

https://www.dumptheguardian.com/news/2025/jun/26/billionaires-wealth-oxfam-report

Billionaires' wealth surged $6.5tn over past decade, Oxfam reports

Real-terms gains of $33.9tn for world's richest 1% 'enough to end annual global poverty 22 times over', charity says

I bet my fiancée that this picture of our cats could get 10 billion boosts on Mastodon.

She said she doesn't believe me. She said there's only 13 million accounts on Mastodon. She said there aren't even 10 billion people on Earth. She said it concerns her that I struggle so hard to comprehend large numbers.

Let's prove her wrong everyone. Boost away and show her just how awesome the Mastodon community is.

Holy #surveillance hell, Batman.

Let me get this straight:

First, they feed your video, which is already stored in their cloud, into an #AI transformer to write descriptions.

Then they feed your descriptions into a pattern learning system (ML, maybe?) to figure out your patterns and habits.

All of this is stored in the cloud. So they not only have your video, but a narrative about your habits, ready to be exfiltrated, monetized, and shared with law enforcement.

#ai #enshittification #RingCamera

https://www.theregister.com/2025/06/25/amazons_ring_ai_video_description/

Amazon's Ring can now use AI to 'learn the routines of your residence'

: It's meant to cut down on false positives but could be a trove for mischief-makers

The Register
aunty Anca's face when i haz not posted a picture every day teh last month. i tryz hard, bro. not so easy to be delicious every day. #dogsOfMastodon #dogsOfPixelfed #dogs
Frickin finally!  #Signal
Behind every pkg install are maintainers doing the hard work. If you maintain anything, big or small — THANK YOU. 🫶 #FreeBSD #community
×
Last week, the vintage IBM 1401 computer at the Computer History Museum started behaving strangely: it wouldn't halt. More specifically, if you had two HALT instructions in a row, it would halt for the first, but when you continued, it crashed mysteriously. Here's how we fixed it.... 1/N
The IBM 1401 computer lets you run code a single cycle at a time, so you can see what happens at each step. (The arrow on the control panel.) But when I tried to single-step through the bad HALT instruction, the computer immediately died in a distant memory location. Now we had two problems. 2/N
I hooked up an oscilloscope and discovered that the computer wasn't running a single instruction cycle. Instead, it ran a few cycles (the pulses below), stopped briefly, ran a few more, irregularly stopping and starting, "building up steam" until it ran thousands of cycles. But why this pattern?
You push the green START button on the console to start the computer after a HALT, and also to single-step it. Hmmm. For convenience, there's also a START button on the card reader and one on the printer. We found that everything worked fine with those buttons. Hmmm.
It turned out that the computer's START button had a strand of wire that shorted one of its contacts. As a result, it would keep re-starting as long as you held the button, blowing through the HALT or single-step until it crashed. The contacts bounced a bit, causing the random gaps we saw.

With the switch fixed, everything worked. At least until next time...

I worked on this with @CuriousMarc, @tubetime, Wren, Shmuel, and others.

I'll leave you with this documentation of the relevant circuitry with inscrutable IBM symbols.
end/N

@kenshirriff @CuriousMarc @tubetime

A classic case of turn it on, and then turn it on again.

@kenshirriff That wasn't a START button, that was a START MISBEHAVING button. In those days, dedicated hardware was needed to make the computer misbehave as software developers were too highly trained to do it purely in software.

These days we have that in software, especially if it's shipped from Redmond, Washington with the help of a large language model. ;-)

@kenshirriff Ah, I was guessing a failed capacitor in the debouncing circuit.
@TimWardCam It turns out that the debouncing is more complicated than that. The switch is double-pole double-throw, with one contact turning it on and the other turning it off. So you're guaranteed not to bounce. Except if one contact is shorted.
@kenshirriff This sounds similar to a bouncing switch, did those systems back then not have an RC circuit to prevent physical switches from sending multiple signal whent actuated ?
Ken Shirriff (@kenshirriff@oldbytes.space)

@TimWardCam@c.im It turns out that the debouncing is more complicated than that. The switch is double-pole double-throw, with one contact turning it on and the other turning it off. So you're guaranteed not to bounce. Except if one contact is shorted.

OldBytes Space - Mastodon
@kenshirriff as a bicycle repairman i can tell you it needs a little spit of wd-40 and will be like new in no time
@kenshirriff My favourite CPU is the PDP-10 KI CPU, that not only let you run single cycles and let you input instructions directly on the front panel, but let you load memory words onto the push buttons and *edit* memory content. I’ve never seen that on any other CPU.
@ahltorp The IBM 1401 lets you load memory from the toggle switches, which is convenient but tedious. Is this the same as what you're describing on the PDP-10?

@kenshirriff If you by toggle switches mean switches with two physical positions, then that was the switches on most DECs.

But this was push buttons with lamps, so you could actually load a word onto the buttons, only flip the individual bits you wanted changed, and then store it back to either the same or another location.

@kenshirriff The PDP-10 KI is also one of the few mainframes I’ve worked with. I was responsible for getting 2 KI CPUs working around 1998, although I didn’t do hardly any of the actual debugging and repairing myself.

@ahltorp @kenshirriff

My PiDP-10 replica, powered by a Raspberry Pi 5. All the switches work. It comes with ITS, TOPS-10 and TOPS-20 operating systems running on top of Linux. Very cool.

https://obsolescence.wixsite.com/obsolescence/pidp10

@ahltorp @kenshirriff I had a front panel for one of those as a kid. My brother fished it out of a dumpster at University of Detroit. We had it on a table in the basement with a large DC power supply. I'd poke around with alligator clips trying to find which wires lit up which buttons. Great fun pretending I had a computer to run.

@ahltorp @kenshirriff

Gould SEL, late 70s, had similar.

@kenshirriff My Dad programmed these things in the early 1960s at Liberty Mutual in Boston. Autocoder, I think. Possibly RPG.

@kenshirriff

Classic case of "You're holding it wrong"

@kenshirriff I love the investigation story!
But what blows my mind is these machines are still running regularly, and fixed so quickly after an issue was found with them!
@kenshirriff this is too obvious but i cannot resist: so you basically solved the halting problem?
@kenshirriff
I wish there was such an easy way to find and fix the troubles I'm having with my smartphone.

@kenshirriff

As a kid I rolled around on the floor and napped by these. I definately wanted a stack of hole punch cards but was thwarted at all turns.

I was not ready to be smacked with nostalgia in this manner.

@kenshirriff “it wouldn't halt.”

Hustle culture is everywhere!

@kenshirriff At least it didn't catch fire after the HALT.
@kenshirriff That's a fascinating look into old tech, thanks!