I am designing an FPGA development board for myself. I want a moderately high speed link (400-500MB/s) to the host PC and I'm considering several options, including an FTDI FT-60x bridge IC. The problem is that this chip has no side channel that would allow me to configure the FPGA, unlike the good old FT-2232H.
This article claims that "USB 2.0 is available on the same connector and can be used as sideband", and suggests using both chips in tandem, with a hub on the USB2 lines for both of them to be available, but routing the USB3 pairs straight to the FT-60x. They are apparently doing this on some of the boards they sell.
So here are my questions:
- Does the USB specification guarantee that USB2 is still available while using the USB3 lane of the same connector?
- Can I really skip the hub on the USB3 lane if I'm using one on the USB2 lane?
- I don't really care if functionality is reduced on a USB2-only port. Can I just skip the hubs altogether and connect one device to each lane?