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Compute module in a PCIe card

Sat Feb 17, 2018 12:11 am

I don't know if this is the right place, but I had an idea for a raspberry pi that could connect into the PCIe slot on a computer and function as a network card so that it could interface with the computer. I was also thinking it could act as a webcam so you could see the screen on your main pc.

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Re: Compute module in a PCIe card

Sat Feb 17, 2018 6:00 am

This is possible via USB device emulation instead of PCI (on select models). PCI would need complicated circuitry designed from scratch (expensive), totally new Windows and Raspbian Linux drivers (expensive) and special (FPGA ?) translation chips (also expensive). No, you can't "do it with the GPIO".

USB device emulation (USB webcam, USB Ethernet card etc.) works almost out of the box if you use Raspbian+Windows and a Compute Module, a Pi Zero (or Zero W/WH) or model A(+). Other models can't act as USB device.

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Re: Compute module in a PCIe card

Sat Feb 17, 2018 2:31 pm

I had a similar idea when the CM first came out and revised it when the zero launched.

I'd do it like this:
  • PCI or PCIe card with USB host controller and one or more USB hub chips.
  • Multiple sockets for CM/pi zero with USB routed from each socket to a hub port
  • PIs runing as USB ethernet gadgets
I abandoned this because:
  • I'm not in a position to design the PCI/PCIe card
  • With the zero you can get the same result just by pluging it into a spare USB port
  • CM3 hadn't been launched at that time so zero was much more cost effective. It still is unless you really need the quad core performance.
  • The clusterhat launched.

Incidentally, you don't need to fake a webcam to see the screen, use VNC over a network. If you really need to see the console boot messages, use the serial port either by adding USB to serial connections or by adding a serial header for each CM socket.
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