PCIe For Hackers: Our M.2 Card Is Done

July 25, 2023 by Arya Voronova 18 Comments

We’ve started designing a PCIe card last week, an adapter from M.2 E-key to E-key, that adds an extra link to the E-key slot it carries – useful for fully utilizing a few rare but fancy E-key cards. By now, the schematic is done, the component placement has been figured out, and we only need to route the differential pairs – should be simple, right? Buckle up.

Getting Diffpairs Done

PCIe needs TX pairs connected to RX on another end, like UART – and this is non-negotiable. Connectors will use host-side naming, and vice-versa. As the diagram demonstrates, we connect the socket’s TX to chip’s RX and vice-versa; if we ever get confused, the laptop schematic is there to help us make things clear. To sum up, we only need to flip the names on the link coming to the PCIe switch, since the PCIe switch acts as a device on the card; the two links from the switch go to the E-key socket, and for that socket’s purposes, the PCIe switch acts as a host.

While initially routing this board, I absolutely forgot about one more important thing for PCIe – series capacitors on every data pair, on the host TX side of the link. We need three capacitor pairs here – on TX of the PCIe switch uplink, and two pairs on TX side of the switch – again, naming is host-side. I only remembered this after having finished routing all the diffpairs, and, after a bit of deliberation, I decided that this is my chance to try 0201 capacitors. For that, I took the footprints from [Christoph]‘s wonderful project, called “Effect of moon phase on tombstoning” – with such a name, these footprints have got to be good.

We’ve talked about differential pair calculations before in one of the PCIe articles, and there was a demo video too! That said, let’s repeat the calculations on this one – I’ll show how to get from “PCB fab website information” to “proper width and clearance diffpairs”, with a few fun shortcuts. Our setup is, once again, having signals on outer layers, referenced to the ground layer right below them. I, sadly, don’t yet understand how to calculate differential impedance for signal layers sandwiched between two ground planes, which is to say – if there’s any commenters willing to share this knowledge, I’d appreciate your input tremendously! For now, I don’t see that there’d be a tangible benefit to such an arrangement, anyway.

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DisplayPort: Tapping The Altmode

July 24, 2023 by Arya Voronova 11 Comments

Really, the most modern implementation of DisplayPort is the USB-C DisplayPort altmode, synonymous with “video over USB-C”, and we’d miss out if I were to skip it. Incidentally, our last two articles about talking USB-PD have given a few people a cool new toy to play with – people have commented on the articles, reached out to me for debugging help, and I’ve even seen people build the FUSB302B into their projects! Hot on the heels of that achievement, let’s reach further and conquer one more USB-C feature – one that isn’t yet openly available for us to hack on, even though it deserves to be.

For our long-time readers, it’s no surprise to see mundane capabilities denied to hackers. By now, we all know that many laptops and phones let you get a DisplayPort connection out of a USB-C port. Given that the USB-C specifications are openly available, and we’ve previously implemented a PD sink using those specifications, you’d expect that we could do DisplayPort with the same ease. Yet, the DisplayPort altmode specification is behind a VESA membership paywall, with a hefty pricetag – a practice of theirs that has been widely criticized, counter to their purpose as a standards organization and having resulted in some of their standards failing.

Not to worry, however – we can easily find an assortment of PDFs giving a high-level overview and some details of the DisplayPort altmode, and here’s my favorite! I also have a device running MicroPython with a FUSB302 chip connected, and a few DisplayPort altmode devices of mine that I can disassemble. This, turns out, is more than enough for us to reverse-engineer our way into an open-source DisplayPort altmode library!

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Weather In Wartime: The Importance Of British Meteorology In WWII

July 24, 2023 by Donald Papp 10 Comments

Weather can have a significant impact on transport and operations of all kinds, especially those at sea or in the air. This makes it a deeply important field of study, particularly in wartime. If you’re at all curious about how this kind of information was gathered and handled in the days before satellites and computer models, this write-up on WWII meteorology is sure to pique your interest.

Weather conditions were valuable data, and weather *forecasts* even more so. Both required data, which relied on human operators for instruments to be read and their readings transmitted.

The main method of learning weather conditions over the oceans is to persuade merchant ships to report their observations regularly. This is true even today, but these days we also have the benefit of things like satellite technology. Back in the mid-1900s there was no such thing, and the outbreak of WWII (including the classification of weather data as secret information due to its value) meant that new solutions were needed.

The aircraft of the Royal Air Force (RAF) were particularly in need of accurate data, and there was little to no understanding of the upper atmosphere at the time. Eventually, aircraft flew regular 10-hour sorties, logging detailed readings that served to provide data about weather conditions across the Atlantic. Readings were logged, encoded with one-time pad (OTP) encryption, then radioed back to base where charts would be created and updated every few hours.

The value of accurate data and precise understanding of conditions and how they could change was grimly illustrated in a disaster called the Night of the Big Wind (March 24-25, 1944). Forecasts predicted winds no stronger than 45 mph, but Allied bombers sent to Berlin were torn apart when they encountered winds in excess of 120 mph, leading to the loss of 72 aircraft.

The types of data recorded to monitor and model weather are nearly identical to those in modern weather stations. The main difference is that instruments used to be read and monitored by human beings, whereas today we can rely more on electronic readings and transmission that need no human intervention.

Ask Hackaday: What’s Linux Anyway?

July 21, 2023 by Al Williams 55 Comments

Any time we mention Linux, it is a fair bet we will get a few comments from people unhappy that we didn’t refer to it as GNU/Linux or with some other appellation. To be fair, they aren’t wrong. Linux is a kernel. Much of what we think of as a Linux desktop OS is really from other sources, including, but not limited to, GNU. We thought about this after reading a report from [The Register] that Linux has nearly half of the desktop OS Linux market. Wait, what?

If you are like us, you probably think that’s a typo. It isn’t. But the more you think about it, the less sense it makes. You know that half of the world’s desktops don’t run Linux. But maybe they mean Unix? Nope. So how can Linux have almost half of the Linux market? That’s like saying nearly half of Hackaday readers read Hackaday, right?

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TV Typewriter Remembered

July 20, 2023 by Al Williams 23 Comments

With the recent passing of Don Lancaster, I took a minute to reflect on how far things have come in a pretty short period of time. If you somehow acquired a computer in the early 1970s, it was probably some discarded DEC, HP, or Data General machine. A few people built their own, but that was a stout project with no microprocessor chips readily available. When machines like the Mark-8 and, more famously, the Altair appeared, the number of people with a “home computer” swelled — relatively speaking — and it left a major problem: What kind of input/output device could you use?

An ad from Kilobaud offered you a ready-to-go, surely refurbished, ASR33 for $840

At work, you might have TeleType. Most of those were leased, and the price tag of a new one was somewhere around $1,000. Remember, too, that $1,000 in 1975 was a small fortune. Really lucky people had video terminals, but those were often well over $1,500, although Lear Siegler introduced one at the $1,000 price, and it became wildly successful. Snagging a used terminal was not very likely, and surplus TeleType equipment was likely of the 5-bit Baudot variety — not unusable, but not the terminal you really wanted.

A lot of the cost of a video terminal was the screen. Yet nearly everyone had a TV, and used TVs have always been fairly cheap, too. That’s where Don Lancaster came in. His TV Typewriter Cookbook was the bible for homebrew video displays. The design influenced the Apple 1 computer and spawned a successful kit for a company known as Southwest Technical Products. For around $300 or so, you could have a terminal that uses your TV for output. Continue reading “TV Typewriter Remembered” →

PCIe For Hackers: An M.2 Card Journey

July 20, 2023 by Arya Voronova 22 Comments

I’ve designed a few M.2 adapters for my own and my friends’ use, and having found those designs online, people have asked me for custom-made adapters. One of these requests is quite specific – an adapter that adds one more PCIe link to an E-key M.2 slot, the kind of slot you will see used in laptops for WiFi cards.

See, the M.2 specification allows two separate PCIe links connected to the E-key slot; however, no WiFi cards use this apart from some really old WiGig-capable ones, and manufacturers have long given up on connecting a second link. Nevertheless, there are some cards like the Google Coral M.2 E-key dual AI accelerator and the recently announced uSDR, that do indeed require the second link – otherwise, only half of their capacity is available.

It’s not clear why both Google and WaveletSDR designed for a dual-link E-key socket, since those are a rare occurrence; for the Google card, there are plenty of people complaining that the board they bought just doesn’t fully work. In theory, all you need to do to help such a situation, is getting a second PCIe link from somewhere, then wiring it up to the socket – and a perfect way to do it is to get a PCIe switch chip. You will lose out on some bandwidth because the uplink PCIe connection of the switch can only go so fast; for things like this AI accelerator, it’s not much of a problem since the main point is to get the second device accessible. For the aforementioned SDR, it might turn out useless, or you might win some but lose some – can’t know until you try! Continue reading “PCIe For Hackers: An M.2 Card Journey” →

Smart Assistants Need To Get Smarter

July 19, 2023 by Zoe Skyforest 81 Comments

Science fiction has regularly portrayed smart computer assistants in a fanciful way. HAL from 2001: A Space Odyssey and J.A.R.V.I.S. from the contemporary Iron Man films are both great examples. They’re erudite, wise, and capable of doing just about any reasonable task that is asked of them, short of opening the pod bay doors.

Cut back to reality, and you’ll only be disappointed at how useless most voice assistants are. It’s been twelve long years since Siri burst onto the scene, with Alexa and Google Assistant following years later. Despite years on the market, their capabilities remain limited and uninspiring. It’s time for voice assistants to level up.

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