SatCat5: UART, SPI And I2C Via Ethernet With FPGA-Based Design

Arty A7-based prototype of SatCat5 with custom switch I/O board. (Credit: The Aerospace Corporation)
Arty A7-based prototype of SatCat5 with custom switch I/O board. (Credit: The Aerospace Corporation)

To the average microcontroller, Ethernet networks are quite a step up from the basic I2C, SPI and UART interfaces, requiring either a built-in Ethernet MAC or SPI-based MAC, with tedious translation between Ethernet and those other interfaces. Yet what if this translation could be done automatically and transparently?  This is what the SatCat5 FPGA-based project by [The Aerospace Corporation] aims to provide: a gateway akin to an unmanaged Ethernet switch that also supports those non-Ethernet links. Recently they answered a range of questions about the project on Hacker News.

The project name comes from the primary target audience: smallsat and cubesat developers, which is an area where being able to route more traffic over a common Ethernet-based bus is a major boon. The provided Xilinx Artix-7-based reference design (pictured) gives a good idea of how it can be used: it combines an Arty A7 development board with a custom PCB containing an Ethernet switch IC (SJA1105), TJA1100 transceiver, two RJ45 jacks and four PMOD connectors, here connected to two UARTs for bidirectional communication between them. Ethernet frame encapsulation is provided using the standard Serial Line Internet Protocol (SLIP), with more details covered in the FAQ. At a minimum an FPGA like a Lattice iCE40 is required, with an MCU capable of using the provided C++ libraries, or a custom implementation.

Thanks to [STR-Alorman] for the tip.

Ethernet For Hackers: Equipment Exploration

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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Tiny Ethernet Routers Now Available In Gigabit Speeds

If you need to move a lot of data, and fast, Gigabit Ethernet is a great way to do it. However, most network hardware outside of datacenters is fairly space inefficient, a headache if you’re building a robot or drone. Enter the Gigablox, a super-compact Gigabit router for just these applications.

The Gigablox takes its mission seriously, with its compact size the ultimate design goal. The entire switch fits on a tiny 45 mm x 45 mm PCB. To this end, it eschews the common RJ45 connector, which is bulkier than necessary. Instead, thin Molex PicoBlade connectors are used for the five ports on board. Cables are included to convert between the two connectors, and obviously crimping ones own is easy to do, too. For those who need to connect more devices, several Gigablox can be hooked up in the same way as any other Ethernet switch. The Gigablox is a non-blocking switch, too – meaning all five ports can run at full speed simultaneously.

The design is the sequel to the SwitchBlox, and the later SwitchBlox Nano, both designed by [Josh Elijah] earlier this year. The pace of development is impressive, and it’s great to see [Josh] bring Gigabit speeds to the compact form factor. We can imagine a few good uses for these boards; share your best ideas in the comments below! Video after the break.

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