DisplayPort: Under The Hood

July 17, 2023 by Arya Voronova 14 Comments

Last time, we looked at all the things that make DisplayPort unique for its users. What about the things that make it unique for hackers? Let’s get into all the ways that DisplayPort can serve you on your modern tech wrangling adventures.

You Are Watching The AUX Channel

With DisplayPort, the I2C bus we’ve always seen come bundled with VGA, DVI and HDMI, is no more – it’s been replaced by the AUX bus. AUX is a 1 MHz bidirectional diffpair – just a bit too complex for a cheap logic analyzer, though, possibly, something you could wrangle with the RP2040’s PIOs. Hacking thoughts aside, it’s a transparent replacement for I2C, so that software doesn’t have to be rewritten – for instance, it usually does I2C device passthrough over AUX, so that EDID data can still be stored in a separate EEPROM chip on the monitor or eDP LCD panel.

AUX isn’t just a differential bus, it’s more pseudodifferential, like USB2 – for instance, AUX_P and AUX_N are used separately, with a combination of 1 MΩ and 100 kΩ pullups and pulldowns signaling different states of the physical connection – for instance, a pullup on AUX+ and a pulldown on AUX- means that an external device has been connected. If you’d like to learn which combination of resistors means what, you can find in the DisplayPort specification, which isn’t distributed openly but isn’t hard to come by, either.

Also, DisplayPort link training happens over AUX, and in order to facilitate that, a piece of DisplayPort controller’s external memory is usually exposed over the AUX channel, through a mechanism that’s called DPCD. If you dig a bit, using “DPCD” as the keyword, you can easily reach into the lower-level details of your DisplayPort connection. Some of the DPCD memory map is static, and some parts are FIFOs you can funnel data into, or out of. You can find a wide variety of documents online which describe the DPCD structure – for now, here’s a piece of Bash that works on Linux graphics drivers for AMD and Intel, and will show you you the first 16 bytes of DPCD:

# sudo dd if=/dev/drm_dp_aux0 bs=1 skip=256 count=16 |xxd 00000000: 0084 0000 0000 0000 0108 0000 0000 0000 ................ [...]

In particular, the 4th nibble (digit) here describes the amount of lanes for the DisplayPort link established – as you can see, my laptop uses a four-lane link. Also, the /dev/drm_dp_aux0 path might need to be adjusted for your device. In case you ever want to debug your DP link, having direct access to the DPCD memory space like this might help you quite a bit! For now, let’s move onto other practical aspects. Continue reading “DisplayPort: Under The Hood” →

Bridging The Gap Between Dissimilar Road Types With Foam

February 10, 2023 by Ryan Flowers 27 Comments

When you think of driving up or down an embankment, do you ever wonder how much foam you’re currently driving on? Probably not, because it hardly seems like a suitable building material. But as explained by [Practical Engineering] in the video below the break, using an expanded material to backfill an embankment isn’t as dense as it sounds.

In many different disciplines, mating dissimilar materials can be difficult: Stretchy to Firm; Soft to Hard; Light to Heavy. It’s that last one, Light to Heavy, that is a difficult match for roadways. A bridge may be set down in bedrock, but the embankments approaching it won’t be. The result? Over time, embankment settles lower than the bridge does, causing distress for cars and motorists alike. What’s the solution?

To mitigate this, engineers have started to employ less dirty materials to build their otherwise soil based embankments. Lightweight concrete is one solution, but another is Expanded Polystyrene (EPS) foam. Its light weight makes installation simple in anything but a strong breeze, and it’s inexpensive and durable. When used properly, it can last many years and provide a stable embankment that won’t settle as far or as quickly as one made of dirt. Because as it turns out, dirt is heavy. Who knew?

Aside from roadways and bespoke aircraft, EPS foam has also been used for making home insulation. What’s your favorite use for EPS foam? Let us know in the comments below.

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An iPhone sits in a users hand open to the YouTube app. What is unusual is that the iPhone is bent in an L shape and is still functioning properly.

First Folding IPhone Doesn’t Come From Apple

November 11, 2022 by Navarre Bartz 26 Comments

Folding phones are all the rage these days, with many of the major smartphone manufacturer’s having something in this form factor. Apple has been conspicuously absent in this market segment, so [KJMX] decided to take matters into their own hands with the “iPhone V.” (YouTube – Chinese w/subtitles via MacRumors).

Instead of trying to interface an existing folding phone’s screen with the iPhone, these makers delaminated an actual iPhone X screen to use in the mod. It took 37 attempts before they had a screen with layers that properly separated to be both flexible and functional. Several different folding phones were disassembled, and [KJMX] found a Motorola Razr folding mechanism would work best with the iPhone X screen. Unfortunately, since the iPhone screen isn’t designed to fold, it still will fail after a relatively small number of folds.

Other sacrifices were made, like the removal of the Taptic Engine and a smaller battery to fit everything into the desired form factor. The “iPhone V” boasts the worst battery life of any iPhone to date. After nearly a year of work though, [KJMX] can truly claim to have made what Apple hasn’t.

Curious about other hacks to let an iPhone do more than Apple intended? Check out how to add USB-C to an iPhone, try to charge it faster, or give one a big memory upgrade.

The Importance Of Physical Models: How Not To Shoot Yourself In The Foot Or Anywhere Else

November 10, 2022 by Al Williams 73 Comments

We take shortcuts all the time with our physical models. We rarely consider that wire has any resistance, for example, or that batteries have a source impedance. That’s fine up until the point that it isn’t. Take the case of the Navy’s Grumman F11F Tiger aircraft. The supersonic aircraft was impressive, although it suffered from some fatal flaws. But it also has the distinction of being the first plane ever to shoot itself down.

So here’s the simple math. A plane traveling Mach 1 is moving about 1,200 km/h — the exact number depends on a few things like your altitude and the humidity. Let’s say about 333 m/s. Bullets from a 20 mm gun, on the other hand, move at more than 1000 m/second. So when the bullet leaves the plane it would take the plane over three seconds to catch up with it, by which time it has moved ever further away, right?

Continue reading “The Importance Of Physical Models: How Not To Shoot Yourself In The Foot Or Anywhere Else” →

A streamlined black boiler with a headlight at the tip dwarfs the 5th wheel trailer and secondary trailer it is attached to.

Bringing A Steam Train Back From Extinction

October 11, 2022 by Navarre Bartz 74 Comments

There’s no denying that while railroads have switched to diesel and electric as their primary power sources, there’s a certain allure to the age of steam. With that in mind, a group of Pennsylvania train fans are bringing the alleged fastest steam train back from extinction.

It takes real dedication to build a 428-ton device from scratch, but these rail aficionados seem to have it in spades. Armed only with the original blueprints and a lot of passion, this team has already finished construction of the boiler and nose of the Class T1 replica which is no small feat. This puts the train at approximately 40% complete.

Some changes are planned for the locomotive including a change to fuel oil from coal and replacing the poppet valves prone to failure with camshaft-driven rotary valves. While not original hardware, these changes should make the train more reliable, and bring the world record for the fastest steam locomotive within reach. If the T1 replica can reach the 140 MPH storied of the originals, it will smash the current record of 126 MPH held by a British train, the A4 Mallard, which would be exciting indeed.

Speaking of Pennsylvania and steam, a trip to Scranton is a must for anyone interested in the age of rail.

Building Bridges In This Week’s Hack Chat

September 16, 2022 by Tom Nardi 5 Comments

In the electronics world, even for the hobbyists, things have only gotten smaller over the years. We went from through-hole components to surface mount, and now we’re at the point where the experienced DIYers are coming around to the idea of using ball grid array (BGA) components in their designs. We’d wonder what things are going to look like in another couple decades, but frankly, it gives us the heebie-jeebies.

So while we’re pretty well versed these days in the hows and whys of tiny things, we see comparatively little large-scale engineering projects. Which is why we were excited to have Andy Oliver stop by this week for the Heavy Engineering Hack Chat. His day job sees him designing and inspecting the control systems for movable bridges — or what many would colloquially refer to as drawbridges.

Now you might think there’s not a lot of demand for this particular skill set, but we’re willing to bet there’s a lot more of these bridges out there than you realized. Andy kicked things off with the revelation that just between the states of Florida and Louisiana, there are about 200 movable bridges of various sizes. On a larger scale, he points out that BridgeHunter.com lists an incredible 3,166 movable bridges in their database, though admittedly many of those are historical and no longer standing. (There really is a site for everything!)

There’s also a huge incentive to keep the existing bridges functioning for as long as possible — building a new one these days could cost hundreds of millions of dollars. Instead, repairs and upgrades are the name of the game. Andy says that if it’s properly maintained, you should get about a century out of a good bridge.

It will probably come as little surprise to find that keeping things as simple as possible is key to making sure a movable bridge can withstand the test of time. While we might imagine that all sorts of high-tech automation systems are at work, and they probably would be if any of us were in charge, Andy says that most of the time it’s old school relay logic.

Even controlling the speed of motors is often down to using beefy relays to switch some additional resistance into the circuit. But when reliability and ease of repair are top priorities, who’s to argue against a classic? Andy recalled a time when a government client made it clear that the only tool you should need to maintain a particular bridge’s control system was a hammer.

Of course, when moving around a million pounds of steel, there’s more than just electrical considerations at play. You’ve also got to take into account things like wind forces on the bridge, specifically that your gears and motors can handle the extra load without tearing themselves apart. The bridge also needs an emergency stop system that can arrest movement at a moment’s notice, but not damage anything in the process.

A lot of fascinating details about these motorized behemoths were covered in the Chat, so we’d invite anyone who’s ever watched a bridge slowly reconfigure itself to peruse through the full transcript. Special thanks to Andy Oliver for stopping by and sharing some of the details about his unique career with the community, and remember that if you’ve got your own engineering stories to tell, we’d love to hear them.

The Hack Chat is a weekly online chat session hosted by leading experts from all corners of the hardware hacking universe. It’s a great way for hackers connect in a fun and informal way, but if you can’t make it live, these overview posts as well as the transcripts posted to Hackaday.io make sure you don’t miss out.

VR Prototypes Reveal Facebook’s Surprisingly Critical Research Directions

June 26, 2022 by Donald Papp 32 Comments

A short while ago, Tested posted a video all about hands-on time with virtual reality (VR) headset prototypes from Meta (which is to say, Facebook) and there are some genuinely interesting bits in there. The video itself is over an hour long, but if you’re primarily interested in the technical angles and why they matter for VR, read on because we’ll highlight each of the main points of research.

As absurd as it may seem to many of us to have a social network spearheading meaningful VR development, one can’t say they aren’t taking it seriously. It’s also refreshing to see each of the prototypes get showcased by a researcher who is clearly thrilled to talk about their work. The big dream is to figure out what it takes to pass the “visual Turing test”, which means delivering visuals that are on par with that of a physical reality. Some of these critical elements may come as a bit of a surprise, because they go in directions beyond resolution and field-of-view.

Solid-state varifocal lens demo, capable of 32 discrete focal steps.

At 9:35 in on the video, [Douglas Lanman] shows [Norman Chan] how important variable focus is to delivering a good visual experience, followed by a walk-through of all the different prototypes they have used to get that done. Currently, VR headsets display visuals at only one focal plane, but that means that — among other things — bringing a virtual object close to one’s eyes gets blurry. (Incidentally, older people don’t find that part very strange because it is a common side effect of aging.)

The solution is to change focus based on where the user is looking, and [Douglas] shows off all the different ways this has been explored: from motors and actuators that mechanically change the focal length of the display, to a solid-state solution composed of stacked elements that can selectively converge or diverge light based on its polarization. [Doug]’s pride and excitement is palpable, and he really goes into detail on everything.

At the 30:21 mark, [Yang Zhao] explains the importance of higher resolution displays, and talks about lenses and optics as well. Interestingly, the ultra-clear text rendering made possible by a high-resolution display isn’t what ended up capturing [Norman]’s attention the most. When high resolution was combined with variable focus, it was the textures on cushions, the vividness of wall art, and the patterns on walls that [Norman] found he just couldn’t stop exploring.

Continue reading “VR Prototypes Reveal Facebook’s Surprisingly Critical Research Directions” →