Virtual Reality Homebrewer's Handbook/vr.iso/vr386/joytimer.asm

Assembly Source File | 1996-03-19 | 12KB | 600 lines

    TITLE    JOYTIMER - CPU INDEPENDANT JOYSTICK READ AND TIMER SPPT

    COMMENT $

    This special cpu-speed independent joystick reader was
    written by Dave Stampe.  It has about twice the resolution
    of normal joystick readers, about 1200 compared to 600.

    It works by counting the number of 1.19 MHz increments of
    the PC timer.  This version re-reads the joystick if the
    timer rolls over: this is becasue the timer handling ISR
    could cause the end-of-count of the joystick to be missed,
    resulting in glitches.

    The timer routines that follow give REND386
    the ability to compile with -3 (386 instructions)
    bypassing the bugs in the _interrupt headers
    in BC 3.1.  If your program uses any other routines
    and then crashes, then save all registers with an inline
    pushad and restore with popad to fix the problem.

    Also has a keyboard interrupt intercept which can
    monitor key status directly

/*
 This code is part of the VR-386 project, created by Dave Stampe.
 VR-386 is a desendent of REND386, created by Dave Stampe and
 Bernie Roehl.  Almost all the code has been rewritten by Dave
 Stampre for VR-386.

 Copyright (c) 1994 by Dave Stampe:
 May be freely used to write software for release into the public domain
 or for educational use; all commercial endeavours MUST contact Dave Stampe
 ([e-mail]) for permission to incorporate any part of
 this software or source code into their products!  Usually there is no
 charge for under 50-100 items for low-cost or shareware products, and terms
 are reasonable.  Any royalties are used for development, so equipment is
 often acceptable payment.

 ATTRIBUTION:  If you use any part of this source code or the libraries
 in your projects, you must give attribution to VR-386 and Dave Stampe,
 and any other authors in your documentation, source code, and at startup
 of your program.  Let's keep the freeware ball rolling!

 DEVELOPMENT: VR-386 is a effort to develop the process started by
 REND386, improving programmer access by rewriting the code and supplying
 a standard API.  If you write improvements, add new functions rather
 than rewriting current functions.  This will make it possible to
 include you improved code in the next API release.  YOU can help advance
 VR-386.  Comments on the API are welcome.

 CONTACT: [e-mail]
*/

/* Joystick reader (c) 1993 by Dave Stampe
/* Contact: [e-mail] */

        $

    .MODEL large
    .386

    extrn _vsync:PROC    ; waits for vert. sync

    .DATA

    PUBLIC _joystick_j1
    PUBLIC _joystick_j2
    PUBLIC _joystick_j3
    PUBLIC _joystick_j4
    PUBLIC _joystick_buttons

_joystick_j1        dw 0  ; /* raw joystick results */
_joystick_j2        dw 0
_joystick_j3        dw 0
_joystick_j4        dw 0
_joystick_buttons   dw 0


    .CODE devices


READ_TIMER     MACRO    ; result will be in ax
    pushf
    cli
    mov    al,00h            ;/* read PC timer */
    out    043h,al
    nop
    nop
    in    al,040h
    mov    ah,al
    nop
    nop
    in    al,040h
    xchg    al,ah
    popf
    ENDM

WRITE_TIMER     MACRO    ; write from BX
    pushf
    cli
    mov    al,34h
    out    43h,al    ; prepare for write
    xor    al,al
    nop
    mov    al,bl
    out    40h,al
    nop
    mov    al,bh
    out    40h,al
    popf
    ENDM


;/********* READ JOYSTICK (RAW COUNT) ************/


mask        equ    [bp+8]          ; arguments

vj1        equ    [bp-2]        ; locals
vj2        equ    [bp-4]
vj3        equ    [bp-6]
vj4        equ    [bp-8]
raw        equ    [bp-10]
last_time    equ    [bp-12]
abort        equ    [bp-14]


;int raw_joystick_read(int mask) ; fills variables, returns 0 if OK
                 ; if failure, retry later on

    PUBLIC    _raw_joystick_read

_raw_joystick_read    proc    far

    .386
    push    ebp
    mov    ebp,esp
    sub    esp,20
    pushf
    push    dx

    test    BYTE PTR mask,-1
    je    quit_now

    xor    ax,ax
    mov    vj1,ax
    mov    vj2,ax
    mov    vj3,ax
    mov    vj4,ax
    mov    cx,5000         ;/* safety timer limit */

waitforit:
    mov    dx,0201h          ;/* wait for timers clear
    in    al,dx
    and    al,0Fh
    and    al,mask
    je    ready_to_begin
    loop    waitforit
    jmp    quit_now    ; no joystick: abort!

ready_to_begin:
    cli
    mov    dx,0201h          ;/* start game port timers */
    mov    al,0ffh
    out    dx,al

    READ_TIMER                ; read PC timer count
    mov    last_time,ax

    in    al,dx            ;/* record game port value */
    mov    raw,al
    and    al,mask
    mov    bl,al
    je      timeout             ;/* catch very short joy time */
    mov    cx,4000         ;/* safety timer limit */
    sti
wloop:
    sti                      ;/* allow ints to occur here */
    cli
    in    al,dx
    mov    raw,al           ;/* game port change? */
    and    al,mask
    xor    al,bl
    and     al,mask
    jne    timeout

    loop    wloop            ;/* safety timer overflow? */

    sti
    jmp     quit_now

    mov    al,mask
    not    al
    mov    raw,al
    mov    abort,ax         ; abort, no bits changed

timeout:
    mov    bl,raw           ;/* record change */
    mov    bh,al

    READ_TIMER                ; read PC timer count
    sti

    test    word ptr long_interrupt,-1
    jne     quit_now
    sub    ax,last_time     ;/* compute delay */
    neg    ax
    jge    posj
    add    ax,_counts_per_tick     ; fixup for timer rollover
posj:
    cmp    ax,1400
    ja    quit_now    ; timer rollover unrecoverable! exit.

    test    bh,8        ;/* update proper joy values */
    je    ns4
    mov    vj4,ax
ns4:
    test    bh,4
    je    ns3
    mov    vj3,ax
ns3:
    test    bh,2
    je    ns2
    mov    vj2,ax
ns2:
    test    bh,1
    je    ns1
    mov    vj1,ax
ns1:
    mov    al,raw        ;/* check if all bits done */
    not    al
    and    al,mask
    cmp    al,mask
    jne    wloop

shorttime:
    mov    ax,vj1          ; copy final values
    mov     _joystick_j1,ax
    mov    ax,vj2
    mov     _joystick_j2,ax
    mov    ax,vj3
    mov     _joystick_j3,ax
    mov    ax,vj4
    mov     _joystick_j4,ax

    mov    ax,raw        ; extract button flags
    not    ax
    shr    ax,4
    and    ax,0Fh
    mov    _joystick_buttons,ax
    mov    ax,0

    pop    dx
    popf
    mov    esp,ebp      ; 0: successful read
    pop    ebp
    ret

quit_now:
    mov    word ptr long_interrupt,0
    mov    ax,cx
    inc    ax        ; will be 1 if too long, else timer ovf

    pop    dx
    popf
    mov    esp,ebp
    pop    ebp
    ret

_raw_joystick_read  endp


;/************ TIMER HANDLING DATA ************/

    .DATA

PUBLIC _timer_tick_count
PUBLIC _timer_vsync_count
PUBLIC _ticks_per_second
PUBLIC _counts_per_tick

_timer_tick_count    dd 0          ; number of interrupts so far
_timer_vsync_count    dw 20000        ; timer counts per video frame
_ticks_per_second    dw 1000        ; counter time basis
_counts_per_tick    dw 65535    ; counter time basis

PUBLIC _timer_interrupt_hook
PUBLIC _frame_interrupt_hook

_timer_interrupt_hook    dd 0    ; timer tick interrupt
_frame_interrupt_hook    dd 0    ; frame-end interrupt (arg=0)

PUBLIC _timer_frame_interval
PUBLIC _frame_resync_interval

_timer_frame_interval   dw 0    ; number of timer ticks per frame
_frame_resync_interval  dw 5    ; number of frames between resyncs

divisor            dw 0    ; used to compute DOS interrupt interval
frame_count          dw 0    ; number of timer ticks to end of frame
frame_sync          dw 0    ; number of frames till sync

long_interrupt         dw 0    ; set if processing took too long

;/************* KEYBOARD MONITOR DATA *************/

;;;PUBLIC _keyflags only for debug!

_keyflags   db 20 dup (0)    ; room for 128 keycodes

    .CODE devices


;/************* TIMER SUPPORT ***************/

;unsigned find_vsync_count()  // finds timer clocks per frame

    PUBLIC    _find_vsync_count
_find_vsync_count    proc    far

    .386
    push    ebp
    mov    ebp,esp

    cli
    xor    bx,bx
    WRITE_TIMER     ; set timer for no overflow

    sti

    call    far ptr _vsync    ; time of frame start
    cli
    READ_TIMER
    push    ax
    call    far ptr _vsync    ; 2xframe delay
    call    far ptr _vsync
    READ_TIMER                ; time of end
    sti
    pop    bx
    sub    bx,ax
    shr    bx,1
    mov     ax,bx             ; compute count

    mov    esp,ebp
    pop    ebp
    ret

_find_vsync_count  endp



;void write_timer(unsigned count) // sets timer period, restarts count


count    equ    [bp+8]

    PUBLIC    _write_timer

_write_timer    proc    far

    .386
    push    ebp
    mov    ebp,esp

    mov    bx,count
    WRITE_TIMER

    mov    esp,ebp
    pop    ebp
    ret

_write_timer  endp



;unsigned read_timer();   // reads current timer count

    PUBLIC    _read_timer

_read_timer    proc    far

    .386
    push    ebp
    mov    ebp,esp

    READ_TIMER

    mov    esp,ebp
    pop    ebp
    ret

_read_timer  endp


;/*********** TIMER ISR *************/

;void timer_isr()    ; does timer interrupt stuff

    PUBLIC    _timer_isr

_timer_isr    proc    far

    .386
    pushf
    pushad
    push    ds
    push    es
    push    fs
    push    gs

    cli
    mov    al,20h
    out    20h,al        ; nonspecific EOI to PIC

    mov    ax,DGROUP
    mov    ds,ax

    inc    DWORD PTR _timer_tick_count

    sub    WORD PTR frame_count,1              ; end of frame?

    test     DWORD PTR _frame_interrupt_hook,-1  ; frame sync on?
    je    no_frame
    inc     word ptr long_interrupt
    push    WORD PTR frame_count                ; frame interrupt hook
    call    DWORD PTR _frame_interrupt_hook
    add    esp,2

    cmp    WORD PTR frame_count,0              ; end of frame?
    jg    no_frame

    sub    WORD PTR frame_sync,1
    jg    no_frame
    mov    ax,_frame_resync_interval    ; SYNC INTERVAL
    mov    frame_sync,ax

    inc     word ptr long_interrupt
    mov    bx,0                 ; resync timer
    WRITE_TIMER
    call    far ptr _vsync
    mov    bx,_counts_per_tick
    WRITE_TIMER

no_frame:
    test     DWORD PTR _timer_interrupt_hook,-1
    je    no_timer_call
    inc     word ptr long_interrupt
    push    WORD PTR frame_count               ; timer tick hook
    call    DWORD PTR _timer_interrupt_hook
    add    esp,2
no_timer_call:
                      ; reset this AFTER for proper args
    cmp    WORD PTR frame_count,0
    jg    notfreset
    mov    ax,_timer_frame_interval
    mov    frame_count,ax
notfreset:
    mov    ax,divisor
    add    ax,_counts_per_tick   ; time to fake 18.2 Hz?
    mov    divisor,ax
    jnc    not_DOS_time

    int    78h        ; call old ISR

not_DOS_time:                         ; no, get out
    pop    gs
    pop    fs
    pop    es
    pop    ds
    popad
    popf
    iret

_timer_isr  endp


;/********* RETURN CURRENT TIME IN MILLISECONDS *********/

;long current_time()    ; returns time in msec

    PUBLIC    _current_time

_current_time    proc    far

    .386
    push    ebp
    mov    ebp,esp

    pushf
    cli
    READ_TIMER
    movzx    ebx,ax
    mov    eax,_timer_tick_count
    movzx    edx,WORD PTR _counts_per_tick
    popf

    imul    edx        ; total count compute
    add    eax,ebx
    adc    edx,0

    mov    ebx,1190    ; compute milliseconds
    idiv    ebx
    shld    edx,eax,16    ; return value in eax and dx:ax

    mov    esp,ebp
    pop    ebp
    ret

_current_time  endp



;/************* KEYBOARD MONITOR *************/


; int is_key_down(unsigned keycode) // returns 1 if key down

keycode    equ    WORD PTR [bp+8]    ; arguments

    PUBLIC _is_key_down

_is_key_down    proc    far

    .386
    push    ebp
    mov    ebp,esp

    mov    cx,keycode      ; isolate bit
    mov    bx,cx
    xor    bh,bh
    shr    bx,3
    and    cx,7
    mov    al,ds:_keyflags[bx]
    shl     al,cl            ; 0 is msb, 7 is lsb
    and    ax,80h

    mov    esp,ebp
    pop    ebp
    ret

_is_key_down  endp



;/*********** KBRD INTERCEPT ISR *************/

;void kbrd_isr()    ; intercepts kbrd interrupt, records key state

    PUBLIC    _kbrd_isr

_kbrd_isr    proc    far
    pushf
    pushad
    push    ds

    cli

    mov    ax,DGROUP
    mov    ds,ax

    xor    ax,ax
    in    al,60h        ; get key code
    mov    dx,ax
    and    ax,07fh
    mov    bx,ax
    mov    cx,ax

    cmp    ax,60h        ; extended code flag
    ja    ignore_it    ; ignore it, just makes keys identical

    shr    bx,3        ; offset in table
    and    cl,7            ; bit shift
    mov    ax,080h
    shr    ax,cl           ; create bit mask: 0 is msb

    test    dx,80h        ; msb set if keyup even else keydown
    jnz    clear_bit

    or    BYTE PTR ds:_keyflags[bx],al
    jmp    done_kbrd

clear_bit:
    not    al
    and    BYTE PTR ds:_keyflags[bx],al

ignore_it:
done_kbrd:

    int    79h    ; call old kbrd isr

    pop    ds
    popad
    popf
    iret

_kbrd_isr  endp

    end