Level    equ   2

         ifp1  
         use   os9defs
         endc  

         mod   eom,name,Sbrtn+Objct,Reent+0,Joy,size

size     equ   .

name     fcs   /JoyStk/
         fcb   $01

* Joystick Read Routine
*
* Entry:
*   X  = $0000 for Right, $0001 for Left
*
* Exit:
*   2,s = param count (should be 4)
*   4,s = addr of 1st param            (joystick number)
*   6,s = size of 1st param
*   8,s = addr of 2nd param            (joystick X)
*  10,s = size of 2nd param
*  12,s = addr of 3rd param            (joystick Y)
*  14,s = size of 3rd param
*  16,s = addr of 4th param            (joystick button)
*  18,s = size of 4th param


Joy      ldd   2,s        get param count
         cmpd  #4         4 params?
         bne   error
         ldd   [4,s]      get joystick num.
* fix up joystick value
         lslb             shift left 3 times
         lslb  
         lslb  
         pshs  b
         lda   #$00       fetch X value
         bsr   JoyPoll
         std   [9,s]      save in param addr
         lda   #$08       fetch Y value
         ldb   ,s+        get joystick selector
         bsr   JoyPoll
         std   [12,s]
* get button value
         clra  
         ldb   #$FF
         stb   $FF02
         ldb   $FF00
         clr   $FF02
         comb  
         tst   [5,s]
         beq   BtnLft
         andb  #$05
         bra   BtnCnt
BtnLft   andb  #$0A
         lsrb  
BtnCnt   lsrb  
         bcc   BtnCnt2
         orb   #$01
BtnCnt2  std   [16,s]     save button
         clrb             no error
         rts   
error    coma  
         ldb   #E$IllArg
         rts   


* Joystick read routine
*
* Entry:
*   A  = value to place in $FF01 (00 for X, 08 for Y)
*   B  = value to place in $FF03 (00 for Right, 08 for Left)
*
* Exit:
*   D  = value

JoyPoll  pshs  a
         lda   $FF01
         anda  #$F7
         ora   ,s+
         sta   $FF01      select X or Y

         pshs  b
         lda   $FF03
         anda  #$F7
         ora   ,s+
         sta   $FF03      select Right or Left

* Low res binary tree search for joystick value
         lda   #$7F       DAC value
         ldb   #$40
         bra   L0122

L0117    lsrb             reset DAC offset value
         cmpb  #$01
         bhi   L0122
         lsra
         lsra
         tfr   a,b
         clra
         rts
L0122    pshs  b
         sta   $FF20
         tst   $FF00
         bpl   L012F
         adda  ,s+
         bra   L0117
L012F    suba  ,s+
         bra   L0117

         emod  
eom      equ   *
         end