Date: Fri, 4 Sep 2015 18:41:05 +0200 From: Jan Bramkamp <crest@rlwinm.de> To: freebsd-usb@freebsd.org Subject: Re: PCIe to USB to PCIe Message-ID: <55E9C9A1.1050407@rlwinm.de> In-Reply-To: <CAA3ZYrBM_FtCGy1MG6LXY1tA-vNsx=xjYE3EpSQzXouEPxrBfA@mail.gmail.com> References: <CAA3ZYrBM_FtCGy1MG6LXY1tA-vNsx=xjYE3EpSQzXouEPxrBfA@mail.gmail.com>
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On 04/09/15 18:06, Dieter BSD wrote: > A very small PCIe x1 card with USB 3.0 controller, a USB cable, > and a small pcb with a PCIe x16 slot. Intended to allow using > x16 video cards with x1 slots, and reducing power/space/cooling > demands on mainboard. > > Claim: "No Driver necessary" > > Can these things possibly work? > > If they do, it seems to me that this would be a great way to > add additional general purpose PCIe slots to any computer that has > USB ports, which nearly all do these days. If no driver is needed, > they should work with any OS. Obviously there is a speed limitation, > but many applications can live with that. > > Sounds too good to be true. Am I missing something? > > http://kaishijia.en.alibaba.com/product/1869213364-221855851/PCIE_PCI_E_Riser_Card_to_USB3_0_and_SATA_Power_Cable_with_PCB_Board_for_Bitcoin_Machine.html > > More here: > http://kaishijia.en.alibaba.com/productgrouplist-221855851/Bitcoin_Mining_cables.html Looks like they (ab-)use the USB3 connectors and cable to carry the PCI-e 1x electrical signals over a few cm (maybe with minimal signal processing/boosting). Don't connect a USB3 host controller to pins on a PCI-e card and expect anything useful to happen. There was a niche market for such hacks when it was profitable to mine coins with GPUs. Mining coins requires only minimal bandwidth between the GPUs and the rest of the system (CPU, RAM) and the goal to maximize the hash computations per second per watt. Under this constrains it makes sense to use low end motherboards with low power CPUs and use such kludges to connect the maximum number GPUs to a mining rig. Its not suitable for general purpose desktops or servers.
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