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I'm trying to understand the relevance of Fast Ethernet in the modern world. What are some current use cases? Or is this project primarily of educational value? (I couldn't find anything in the docs.)

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There are tons and tons of industrial products that use Ethernet for communication, but don't necessarily need a ton of data. Maybe a C&C machine, or a 3D printer, or an oscilloscope, or an automotive network. For any kind of command-and-control applications, 100 Mbit is more than fast enough. Even 10 Mbit would be plenty for lots of systems.

Around the house, you'll find 100BASE-T Ethernet on wired security cameras, televisions, printers, home-automation, and lots of other stuff too.

As a product designer, there are lots of reasons why I might want to put Ethernet on my widget. It's more robust than wifi, it's lower-power, and it's cheaper. It also has much longer range. I might also like to use Power-over-Ethernet to avoid the need for batteries or an electrical outlet.

Ethernet is also much easier to handle than wifi, from a software perspective. And there are lots of products don't really need more than 10-20 KB/sec of data throughput.

I worked on a product in 2022 that settled on 100BASE-T Ethernet as the right design fit (as a backup to wifi), and it was a great choice for the project. I'd make the same choice again today, for a similar system. 10BASE-T is pretty much gone at this point, but 100BASE-T is alive and well as the lowest common-denominator.

Pretty much all networking gear on the market supports 100BASE-T flawlessly, even if the rest of the devices on the network are 1000BASE-T or 2.5GBASE-T. Almost every laptop (or USB) Ethernet adapter also supports auto-negotiate and auto-crossover, meaning that you could plug your laptop right into some device's 100BASE-T port and start talking to it.

FPGAs are typically a little too pricy for consumer gear, but they're incredibly common in higher-margin commercial, industrial, and military equipment. And if your design already has an FPGA for some reason or another, why not use it to provide Ethernet as well? Cuts down on the number of chips you need to use in your design.

Even most Smart-TVs still have only 100BASE-T ethernet connections, but this is still enough to stream a high-bitrate 4K DoVi/HDR10+ movie.

Some 4k blu-rays will peak at greater than 100Mbps, so if you want to stream those without recompressing, you may need a big buffer or gigE.

No one is bringing a raw Blu-Ray signal into the back of their TV over Ethernet though— Netflix's 4K streams cap out at around 16mbps, which is a tiny fraction of that.

Well sure, cause there's not enough bandwidth :P otherwise, why not? The tv probably has a good enough decoder, just no disc drive.

Netflix streaming isn't exactly a high-bitrate movie either though.

> No one is bringing a raw Blu-Ray signal into the back of their TV over Ethernet though— Netflix's 4K streams cap out at around 16mbps, which is a tiny fraction of that.

Who cares about internet streamers? Plenty of us definitely are bringing raw Blu-Ray signals in to the back of our TV over ethernet. Disk space is cheap, transcoding is slow and lowers the quality, so when I rip my movies I just do what the pirates call a "remux" where I keep the exact same audio and video streams as are on the disc and just slap them in to a MKV container for my convenience.

It's not super common for UHD Blu-Rays to crack 100mbit/sec but the spec allows for up to 144mbit/sec. I've casually looked in to it in the past and AFAIK Gemini Man is the current leader, with regular spikes to the 120mbit/sec range and one scene transition actually violates the spec by my count, hitting over 150mbit/sec.

Okay, fair. I think that's a use case that would likely be pretty far outside of what the manufacturer would be envisioning when they spec what kind of Ethernet port to put on the TV though— from their point of view it would be purely for firmware updates, spyware, and the built in streaming apps; anything more complicated than that will be coming from an external device through the HDMI port.

Thanks for this - I now realise that I had 10BASE-T and 100BASE-T mixed up when I asked the question.

P.S. Too many generations... I still remember Token Ring and coax Ethernet fighting it out, and even today I run a mix of four different speeds at home, 1G/2.5G/10G and 25G. Everything's become a bit of a blur. :)

Smaller devices that don't need to send or receive more than 100mbits? Devices that don't want to consume more energy than necessary? (I think gigabit is more power-hungry).

Wifi isn't practical for all use cases either.

100mbit ethernet is very common in industrial use. It is also more robust EMI/RFI and easier to get past EMC certifications.

And 10Base is evolving, not going a way. Base-T1L spec got recently released. It does full-duplex 10mbit over a single twisted pair. It is rated for +1000meter cables. 1/10 of the speed of 100BaseTX, but 10x the range.

1Gbps may actually be easier than 100mbps from an EMC perspective. 100mbps links are infamous for trashing HAM frequencies. Indeed, when I played around with my RTL-SDR at home, the FM spectrum was littered with harmonic spikes originating from the one and only 100mbps link I had at the time.

Another good exampe is the industrial space. Factory machinery used to communicate over serial type interfaces, but now theres a push to move to EtherCAT which is a determistic protocol built on top of Fast Ethernet.

There is a GigE specification now too, but if all you're doing is controlling some motors you don't need that much throughput.

EtherCAT is not build on top. EtherCAT is just a bit-chain who looks like valid Ethernet frames so that the controller side, and the switch side can handle them like any other regular Ethernet frame. The device aka slaves need a special implementation that just goes through the frame in real-time and changes the bits in real-time and at the end modifies the CRC accordingly in real-time. So, it is not built on top.

On top there are other things like ProfinetIO.

EtherCAT is built on top of IEEE 802.3 Frames, you're right that there is a special controller but those interface over MII to a standard Ethernet PHY.

They don't look like valid Ethernet Frames, they are valid Ethernet Frames. Ethercat embeds its Ethertype within the frame the same way that other protocols do.

As you say, EtherCAT does its own thing with the frames, to get the real-time determistic performance it needs, but EtherCAT and other 802.3 Frames can co-exist.

https://www.ethercat.org/pdf/english/EtherCAT_Introduction_0...

Slide 25-32 are a good high level overview of possibilities. Slide 32 shows a setup with Co-Existance.

Thanks for referencing. I still have one of the original specification somewhere in my closet, when I was asked to review it.

They are made to look alike valid Ethernet frames. The idea was: how to make Interbus look alike Ethernet and how to make some patents to make money out of it. Originally you had to buy the controllers from Beckhoff. Now they are integrated by many µC, but still they have to pay licensing fees to Beckhoff.

A number of FPGAs come with hardware Ethernet peripherals built-in so I'm guessing this is for fun.

Brain fart - didn't register that this is a PHY, not a peripheral core. Different parts.

Same reason virtually all keyboards and mice still use USB 1.2: if you don't need the speed, why go through all the trouble trying to design for a way more complicated standard?

You can bitbang USB over a wet string with an ATtiny. If you want USB 2.0 you need dedicated hardware for it in your MCU, and you need to pay some attention to your PCB design. With USB 3.0 you need an expensive MCU, and you need to actually pay close attention to PCB design to ensure the signal remains intact. USB 3.1 and above is basically magic.

The same will apply to Ethernet: stick to the slowest standard which is sufficient for your application to save yourself a lot of headache.

The ESP-32 is a $2 microcontroller that has a Fast Ethernet MAC. It won't handle gigabit, but it can do plenty. Having support for 100BASE-TX solves a lot of problems with Wi-Fi.

There are several long-range wireless gateways that use Fast Ethernet just because the RF link is the bottleneck. When you run up against physics, there's just no point in supporting a gigabit path in/out.

Fast Ethernet is better than no Ethernet, and gigabit is unachievable in low-end FPGAs.

GigE not being achievable on low-end FPGAs explains it really well, thank you.

At the moment I have Artix 7 with ancient gigabit PHY running GigE. In Xilinx eco-system it is pretty low-end device.

20 Euro Colorlight 5A FPGA boards from Aliexpress come with dual Gigabit Ethernet ports, open toolchain to build a SoC that can access them as well.

LiteX allows me to use it as a Gigabit Ethernet powered logic analyzer with a lot of inputs.

No, if the FPGA can do this, then it would be perfectly capable of interfacing to a gigabit PHY or a parallel/serial converter for a Gigabit SFP.

RGMII only requires a 125MHz clock; which is not particularly fast. It depends what you mean by "low-end", but you can certainly implement gigabit Ethernet on something like an Intel/Altera MAX 10 for example. It does rather depend on what you want to do with it though.

But if you have IO fast enough to do direct 100Mbps Ethernet, you can do GMII or RGMII to a gigabit PHY (or a parallel to serial converter to talk to an SFP). I think the project here goes through MII internally anyway (I only skimmed it) so it would actually take more space on the FPGA fabric than using a PHY…

So apart from being fun, maybe the main benefit would be less board space because it doesn’t need the PHY chip? (But also potentially lots of disadvantages practically).

Yeah. A Fast Ethernet PHY that does 10/100 Ethernet with auto-negotiation, auto-MDI/MDIX etc. is less than $1 in quantity and fits in a footprint a couple of mm on each side.

I think this is a "because I can" sort of thing.

Industrial systems for one

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