If you want high-speed io to USB the FX3 is probably one of the best bets.
You see it frequently used on logic analyser and software defined radio
boards between the USB and the FPGA.
https://www.cypress.com/products/ez-usb-fx3-superspeed-usb-30-peripheral-controller
There are several EZ-USB FX2LP boards on eBay at $4-6. That is only USB
2.0 but might be a good option -- but I am up to speed with the FT245RL.
I actually think that USB 2.0 full speed at 480 Mbps would be adequate
in most cases. We would probably only realize 300Mbps or so, but I
think even transferring at that rate could impact real time
performance. The FT60x with USB 3.0 will do 54Gbps (actual). I imagine
that the EZ-USB FX3 would be similar. But that rate may not be
necessary. One would have to collect some measurements to really
understand (a) the required throughput, (b) the MCU overhead for making
the transfers, and (c) the effect on real-time performance.
Why not use the ETM?
The solution should not conceptually depend on any particular
transport. Any transport that can meet the data rate requirements
(whatever those are) and interferes only minimally with CPU performance
could be considered. So I suppose that ETM might also be a possibility
on many ARMs, but not a general solution that I would personally be
interested in.
