Ninja tap

tested on BlueMSX
you have to stand in front of PLAYER on each player
blue control player by default
red control w
green control joystick 1 up
yellow control joystick 2 up
only after push Space Key for starting

Just test it on SX2, as Jipe said, i can use 2 controllers in game after menu.
When a NinjaTap is plugged, no joystick detected

I think it is possible to add SELECT and START buttons from a FM Towns controller without add extra hardware.

; ntap access
GETNIN:
 ....
 ....
;/////////////////////////
   ld   a,h
   pop   hl
   call addSelStart
   ld   (hl),a      ;joy1
   inc   hl
   ld a,e
   call addSelStart
   ld   (hl),a ;  e      ;joy2
   inc   hl
   ld a,d
   call addSelStart
   ld   (hl),a ;  d      ;joy3
   inc   hl
   ld a,c
   call addSelStart
   ld   (hl),a ;  c      ;joy4
   inc   hl
     
; restore port (6,7,8=h)
   ld   de,0ff3fh
   call   porsel
;   ld   a,15
;   out   (0a0h),a
;   in   a,(0a2h)
;   or   3fh
;   out   (0a1h),a
   pop   af
   ret

And this is the function that replaces UP+DOWN with SELECT and LEFT+RIGHT with START(RUN)

; process FM towns extra buttons
; a = A B Sl St Up Dw Lf Rg 
  addSelStart:
  ld b,a            
TestForSelect:      
  and 11110011b     ; test only wanted bits 
  jr nz, TestForRun ; if U+D not active at the same time, test for L+R
  ld a,00001100b    ; deactivate up+down bits
  or b              
  and  11011111b    ; activate Select bit
  ld b,a              
TestForRun:         
  and 11111100b     ; test only wanted bits
  ld a,b            ; last return value  
  ret nz            ; if U+D not active at the same time, return last value
  ld a,00000011b    ; deactivate left+right bits
  or b              
  and  11101111b    ; activate Run (start) bit
  ret

Hi Jipe. Thanks for testing.
This morning I was able to set the openMSXdebugger to keep testing the patch. I had the same behaviour -> black screen. Investigating if further I have found that the game fulfills the space after 0xd400 up to df92.
Then I changed the patch to begin at 0xe000 and made some tests with the debugger and it seems to be working, by inserting manually the bytes that shoud be read from the ninja tap on the emulator addresses and running step by step.
I have uploaded the new patch code and a disk image with the patched binary (Q) and the Tap Function (M) and a basic loader (muhonP.bas) to github.

You had already did that? I must have missed that
Great!!!