Thank you all for the help

I was sure that the table had something weird, only i coudn't see what ... the question rises anyhow: why should those bits be counted from right to left? By convention?

The code works and it's very clear: essentially you "flatten" all the 4 view bits (5th to 8th) to "1111" with viewval = (viewval | 0xf0) and then assign the zero to the desired view bit with viewval = viewval & 0xef for bit 5, and so on.

To complete it it should be introduced some flag to avoid the view "shaking" while keeping the button pressed. I made a try, even if it doesn't work (it detects the first press, then nothing)


Code:

static READ32_HANDLER( port1_r )
{
      static UINT8 cur_view = 0;
      UINT16 viewval = readinputport(1); //actual values stored in memory
      UINT8 button_pressed = viewval & 0x0010;
      int diff=1; //the flag
     
if (button_pressed){diff=0;}//if you release the button, the cycle is ready to be triggered by button press

if (!button_pressed && diff==0) // button is pressed and the button was released
{
 diff=1; //this should stop the cycling untill the button is released ...
 cur_view++;
 
         if (cur_view == 4){cur_view = 0;}

         switch (cur_view)
         {
         case 0:
         viewval = (viewval | 0xf0) & 0xef;
         break;
         case 1:
         viewval = (viewval | 0xf0) & 0xdf;
         break;
         case 2:
         viewval = (viewval | 0xf0) & 0xbf;
         break;
         case 3:
         viewval = (viewval | 0xf0) & 0x7f;
         break;
         }
}
return (viewval << 16) | viewval;
} 

Any idea on what's wrong here? 

Thanks!!