Japanese developer 173210 just released CapusbPSP. As the name reveals (kind of), this is a tool to capture usb traffic from the PSP.
173210 started working several years ago on the PSP’s usb drivers analysis, which could be leveraged on the Vita as well: the PSP’s usb communication to a PS2/PS3 also works from within the PSP emulator on the PS Vita.
Capusbpsp’s source code has been released to contribute to this quest. 173210 hasn’t given on on his project to understand and reverse engineer USBPSPCommunicationDriver (a project started back in 2013), and is asking for help completing the task.
If you can help, feel free to lend a hand to 173210 in our forums.
Once compiled, capusbpsp can be run as a plugin on any CFW-enabled PSP
Download
You can download CapusbPSP here (source code)
Source: 173210 on /talk