An old Sony patent from 2005 shows an idea the then gaming giants had to hook up your PSP with a PS2 controller.
The thinking behind it was that, via a wired or wireless link, you could play PS or PS2 games on your PSP using the original controls:
"Thus, when playing a game ported to execute on the portable gaming platform, the user can utilize substantially, if not identically, the same control sequence as used with the console system".
Maybe they were skeered that folks would not get their heads round the PSP controls and wouldprefer
carrying around an extra controller in order to replicate that original console action.
No word on whether this has been re-patented for the PSP Slim'n'Tasty and PS3...