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Comment by haunter | Hacker News Reader

$400 (16GB DDR5) and $500 (32GB DDR5) because that's not in the blog post.

But I have some questions:

Why the weird form factor? Mini-DTX is supported by a lot of cases but as a motherboard form factor it's incredibly niche compared to Mini-ITX and especially Micro-ATX.

Edit: DTX supposed to be an open standard but it's already a "dead" platform https://en.wikipedia.org/wiki/DTX_(form_factor)

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?

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Unless something is particularly unique with this HiFive revision you can use PCIe SSDs it just looks like this one is relatively lane starved and you'll need to eat the PCIe slot to do so (it's a x16 slot physically but only x4 in terms of actual wired lanes). The E-keyed slot is listed as SDIO, but even if it had PCIe wired up it'd be a max of x2 lanes.

> 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

> 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)

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.

> 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.

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.

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

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.

Honestly, this type of board is something that you aren't really going to just install in a case and forget about it. You are most likely going to have this on a test bench so you can swap out all kinds of different hardware for validation.

Buttons on the bottom for power/reset, 2 different JTAG ports, DIP switches for settings, and remote board management aren't things that are normally found on consumer boards. Mini DTX probably allows them to have a marginally smaller width compared to Micro-ATX while still allowing space for all of that debug functionality with a 2 slot graphics card installed. eMMC is also kind of important for a SOM as well.

if you look on the product brief, the M.2 E key is only hooked up via SDIO, not PCIe

mini-dtx is mini-itx with space for an extra slot - in practice a lot of cases support that as a mini-itx board plus dual slot gpu has the same footprint.

> "As a result of increased production and economies of scale, we’re excited to announce we are able to lower the price to just $399 for the 16GB version and $499 for the 32GB version"

? Also, both now listed as No Stock Available

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