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Comment by MobiusHorizons | Hacker News Reader

> Why the eMMC? There is an M.2 E key but that's for wireless connection only. Is it a platform limitation that M.2 SSDs can't be used?

Presumably very limited pcie bandwidth. You should think of this more like a raspberry pi than a pc motherboard.

E key slots typically provide 1 lane of pcie 2.0 (even on systems with 3.0 available), while m.2 is 4 lanes and frequently faster pcie 3.0

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Just checked: looks like it does provide a full size pcie slot. My guess is that the intended use case is for developers testing compatibility. You could almost certainly plug in an nvme drive through an adapter to that full size slot (although booting from it would likely require a custom uboot build) but if you use up the one slot for storage, you can’t plug in any other peripherals to test.

It's a 16x slot, but it only provides 4 lanes of PCIe 3.0

Appears to be a SoC limitation, which only has a single 4x PCIe 3.0 interface, and doesn't appear to support bifurcation (splitting into two 2x slots, or four 4x slots). You could probably throw a PCIe switch on it, but PCIe switches are expensive.

The SoC wasn't designed for this product, it was designed by 3rd party company for computer vision/robotics/manufacturing use cases.

Yeah, the Intel Horse Creek chip with the same SiFive P550 cores was probably much better on I/O -- and likely DDR IP as well, if they used their good stuff -- but for some reason Intel decided not to go to mass production on them, despite showing off a working board at a trade show in IIRC September 2023.

Sometimes not even that. On my motherboard the E key slot is just USB.

EDIT: Originally said USB3, but it's actually USB 2.0.

I believe the slot usually passes 4 wire usb2 as well as 1 lane if pcie. I had no idea usb3 was an option. How does that affect compatibility?

Ah my mistake, it is in fact USB 2.0. There does exist an M.2 key which can provide USB 3, but that's Key B not E.

> You should think of this more like a raspberry pi than a pc motherboard.

For the price tag I think it should be more like a motherboard. Especially when Raspberry Pi 5 has official m.2 hats.

This is effectively an industrial dev board not a product for normal users. They are usually expensive because of low volume

You can connect M.2 NVMe, it just doesn't have a dedicated slot. If you're looking for a cheap device to plug a bunch of different PCIe devices into a RISC-V development board is probably not your ideal pick, look at a normal computer.

> You should think of this more like a raspberry pi than a pc motherboard

Thanks that makes perfectly sense! I kind of want to buy one now (too bad single 32GB boards can't be bought, minimum order is 256)

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