Designing an Ethernet Switch ASIC · Tales on the wire&darr;<br>Skip to main content<br>Tales on the wire

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AI disclosure: All bugs are 100% human made.<br>It seems I have just built the world’s first open source switch ASIC and I am getting it back from the fab mid november.Switch floorplan render with area density view enabled, occupying 711.2 x 325um of area. The first version of this chip is currently taped out on the Tiny Tapeout gf26b shuttle chip, part of the second wafer.space run. Silicon bring-up is expected to start 2026-11-15.<br>Here is its repository :Essenceia/ethernet_switch_asic

Open source sillicon for a 100Mbps unmanaged cut-through ethernet switch.<br>Verilog

Buckle up and welcome to the tale of more madness.

Recommended soundtrack for reading: Taishi - Reverie for Another Sphere

Where are the open source networking ASICs?<br>Recent FCC decisions have put the central importance of networking equipment top of mind, and in doing so, have also put the total absence of any entirely open source networking equipment hardware at the top of my mind.<br>Although Open Source Silicon is in its infancy we are currently seeing a number of projects being designed, tested, and for the most ambitious ones, even tapedout with some proven silicon already in the wild.<br>Silicon proven RISC-V SoC made as part of wafer.space run 1. Yes, it runs Linux.That said, the vast majority of the most ambitious projects are predominantly RISC-V SoCs.<br>Surprisingly, there has been much less interest in building open hardware for networking equipment.<br>Well .. unsurprisingly actually … networking equipment is far less &ldquo;sexy&rdquo; than CPUs and has thus received much less attention from the open source community. On the other hand, this means there&rsquo;s a huge untaped boulevard of projects open to anyone with more time than common sense to build open source networking equipment chips!<br>Because, on the other side of the great silicon divide, the world of open source networking equipment is actually quite rich, both in terms of its flourishing software ecosystem and the open PCB/electronics ecosystem, with a flurry of fully featured open source routers available. Yet, due to the current ecosystem&rsquo;s limitations, under the hood, these are all still all running closed-sourced, blackbox proprietary chips for the central compute and routing tasks.<br>So what would it take to build a router chip?<br>It&rsquo;s a very ambitious project, since a router involves a complex SoC needing both a powerful enough CPU to run the networking stack alongside specialized networking hardware, and analog frontends for the wired and wireless connections. Since building a full router outright is much too ambitious of a greenfield project for a single person to ever hope to pull off, let&rsquo;s begin with a more approachable first step: building a switch. After all, although most people only have one router, you can have a number of smaller switches, and we also don’t have any open source chips for those.<br>Oh and, I am not talking about building an FPGA switch, oh no, I am talking about building a switch ASIC, taping it out and then proving the silicon works.<br>Switch Flavors<br>Before we start figuring out what kind of switch we want to build, let me give you a quick overview of the different flavors of switches out there. Readers deeply familiar with networking equipment can skip this part.<br>Glossary<br>Physical Layer<br>Ethernet supports multiple physical layers, outlined in the 802.3 IEEE spec. Each clause in the spec defines the underlying medium characteristics for carrying the Ethernet protocol over the medium at a given bandwidth.<br>Both a 10 Gb fiber Ethernet link and a 10 Mb coaxial cable can carry Ethernet packets and, to the layers above the physical layer the packets will look exactly the same.<br>Where they will differ is at the physical layer and, outlined in the spec is precisely how, with which timing and with what encoding data will be transmitted over the medium.<br>This ensures that devices made by different manufacturers agree on what &ldquo;talking Ethernet&rdquo; looks like. making them interoperable.<br>So one of the first questions I must answer is which physical layer my switch should support. This will define how much traffic I must route, how fast I should do so and how much bandwidth I can carry.<br>Managed vs Unmanaged<br>The second question is: what type of switch do I want to build?<br>There are two big families of switches: managed and unmanaged. As the name implies, managed switches can be configured and managed from the outside. This allows for much smarter routing, such as supporting different VLANs.<br>While unmanaged switches are essentially unconfigurable pieces of networking equipment that you plug into your network and just work (until power surge do you part).<br>Cut-through vs Store-and-Forward<br>The last switch characteristic is cut-through versus store-and-forward.<br>Cut-through switches start forwarding a packet while the...