Key / Joystick question (Gamestart with phy.button)

[top-specci]

Hi,
I just build up my Bartop, now I have 3 buttons on the front (1P - Coin - 2P).
and on the top there are 7 buttons in two rows, first 3 buttons, behind 4 buttons.

In principle, all buttons and the joystick (connected with a Zerodelay USB connector) is working.

I.e., when starting ZX-Spectrum Emulator and a game, two questions:

• I want to use always kempston joystick (most games support this joystickk),
  I already add this line: input_libretro_device_p1 = "513" in the retroarch.cfg from zxspectrm-folder.
  How can I select the Kempston joystick now in the start menu from the games? There is the need to press "2" for Kempston.
  Only using the virt.Keyboard and selecting (i.e.) the "2" ?

And:

• To start the game, some games expect to press the "5" button, others the "0".
  Is it possible that I can use my phy. "1 Player" button to start theses game. Can I map the key to this button?
  How can I solve the issue that some games exepct the "5", others the "0"?
  Can the phy. button send both keystroke, first "5", than "0" ?
  (I think there is no game individuell joystick setting possible, or can the game load a special joystick setting?)

[top-specci]

Hi,
my bartop is now finished and running, but still the (little) "problem" tp start the programs.

As written, some (ZS-Spectrum) Games need to press the "5" on the keyboard to start, others the "0" .

Is there an option to define the (phy.) 1P button to the "5" for Game-A, and for Game-B the 1P button to "0" ?
So a game specific setting?

Or any other idea or hints here ?

Thanks,
Martin