GIMX can now control a PS4 over USB in both Linux and Windows! I will release in the next days a new firmware for the DIY USB adapter and a new GIMX software.
The connection diagram is as follows:
DS4 -- PC -- USB to UART adapter -- AVR USB board -- PS4
The DIY USB adapter is unchanged: it is composed of a AVR USB board and a USB to UART adapter.
The AVR USB board (such as a Teensy 2.0) enumerates similarly to a Hori Pad 4 FPS.
When the AVR USB board receives a control request from the PS4 that is part of the authentication scheme, this request is forwarded to the USB to UART adapter, then to the PC, and finally to the DS4. The reply from the DS4 takes the opposite path.
As for the 360, authentication data goes in both direction, but for the PS4 it is periodic. GIMX processes authentication data from the serial port and from the DS4 asynchronously. This makes data forwarding fast and efficient.
The drawback compared to the bluetooth solution is that it’s not possible to emulate touchpad & motion sensing controls, which are required in some games (mostly in PS4 exclusive ones). The other adapters (XIM/Titan/VenomX) have these limitations, and there no work-around yet. At least the USB solution is usable in most cross-platform games.