fceu-packed [FourScore].elf -   NES Four Score.
fceu-packed [4-PlayerAdapter].elf -   Famicom 4-Player Adaptor.

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    :
https://github.com/AKuHAK/Fceumm-PS2/tree/9df6a5d5afc70bc7386579c726c0daebb056dff0

* browser.c -    .
browser_primitive("FCEUltra PS2 (AKuHAK 160627 +Multitap)","Browser", &BG_TEX, menu_x1, menu_y1, menu_x2, menu_y2);

* cnfsettings.c -    3-  4- ,  .

* ps2input.c -  :
if (mtapGetConnection(0) == 1) {
    NESButtons |= ( Get_PS2Input(2) << 16); //third player
    NESButtons |= ( Get_PS2Input(3) << 24); //4th player
}
     Four Score    4-Player Adaptor:
FCEUI_SetInputFC(SIFC_4PLAYER, NESPads, attrib);

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 :
*  ,  .
*  4-Player Adaptor   .
*     .
*    .