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Ethernet For Hackers: Transformers, MACs And PHYs

March 7, 2024 by 21 Comments

We’ve talked about Ethernet basics, and we’ve talked about equipment you will find with Ethernet. However, that’s obviously not all – you also need to know how to add Ethernet to your board and to your microcontroller. Such low-level details are harder to learn casually than the things we talked about previously, but today, we’re going to pick up the slack.

You might also have some very fair questions. What are the black blocks near Ethernet sockets that you generally will see on boards, and why do they look like nothing else you see on circuit boards ever? Why do some boards, like the Raspberry Pi, lack them altogether? What kind of chip do you need if you want to add Ethernet support to a microcontroller, and what might you need if your microcontroller claims to support Ethernet? Let’s talk.

Transformers Make The Data World Turn

One of the Ethernet’s many features is that it’s resilient, and easy to throw around. It’s also galvanically isolated, which means  you don’t need a ground connection for a link either – not until you want a shield due to imposed interference, at which point, it might be that you’re pulling cable inside industrial machinery. There are a few tricks to Ethernet, and one such fundamental Ethernet trick is transformers, known as “magnetics” in Ethernet context.

Each pair has to be put through a transformer for the Ethernet port to work properly, as a rule. That’s the black epoxy-covered block you will inevitably see near an Ethernet port in your device. There are two places on the board as far as Ethernet goes – before the transformer, and after the transformer, and they’re treated differently. After the transformer, Ethernet is significantly more resilient to things like ground potential differences, which is how you can wire up two random computers with Ethernet and not even think about things like common mode bias or ground loops, things we must account for in audio, or digital interfaces that haven’t yet gone optical somehow.

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Ethernet For Hackers: Equipment Exploration

February 28, 2024 by 28 Comments

Last time, we talked about the surface-level details of Ethernet. They are fundamental to know for Ethernet hacking, but they’re also easy to pick up from bits and pieces online, or just from wiring up a few computers in your home network. Now, there’s also a bunch of equipment and standards that you will want to use with Ethernet – easy to find whether used or new, and typically as easy to work with. Let’s give you a few beacons!

Routers And Switches

Whenever you see a box with a few Ethernet ports, it’s either referred to as a router, or a switch, sometimes people will even use the word “hub”! Fortunately, it’s simpler than it may seem. A router is a smart device, typically with an OS, that ties two or more networks together – routing packers from one network to another, and typically taking care of things like handing out local IP addresses via DHCP. A switch merely helps Ethernet devices exchange packets between each other on the same level – it’s typically nowhere near as smart as a router gets. Oftentimes, a home router will contain a switch inside, so that you can plug in multiple of your home devices at once. That’s the main difference – a switch merely transmits packets between Ethernet-connected devices, while a router is a small computer taking care of packet forwarding between networks and possibly including an Ethernet switch on the side.
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Ethernet For Hackers: The Very Basics

February 12, 2024 by 92 Comments

Ethernet is ubiquitous, fast, and simple. You only need two diffpairs (four wires) to establish a 100Mbit link, the hardware is everywhere, you can do Ethernet over long distances easily, and tons of the microcontrollers and SoCs support it, too. Overall, it’s a technology you will be glad to know about, and there’s hundreds of scenarios where you could use it.

If you need to establish a high-bandwidth connection between two Linux boards in your project, or maybe a Linux board and a powerful MCU, maybe make a network between microcontrollers, Ethernet’s your friend. It also scales wonderfully – there’s so much tech around Ethernet, that finding cables, connectors or ICs tends to be dead easy. Plus, the world of Ethernet is huge beyond belief. Ethernet as most of us know it is actually just the consumer-facing versions of Ethernet, and there’s a quite a few fascinating industrial and automotive Ethernet standards that flip many of our Ethernet assumptions upside down.

Now, you might be missing out on some benefits of Ethernet, or perhaps misunderstanding how Ethernet works at all. What does it mean when a microcontroller datasheet says “has Ethernet interface”? If you see five pins on an SBC and the manufacturer refers to them as “Ethernet”, what do you even do with them? Why does the Raspberry Pi 4 SoC support Ethernet but still requires an extra chip, and what even is GMII? Continue reading “Ethernet For Hackers: The Very Basics” →