page 60,132

; Copyright (C) 1988  Mark Adler  Pasadena, CA
; All rights reserved.

 title ZAP - screen saver for the EGA or VGA

comment #

Version history -

1.0     18 Nov 1988     First public version
1.1     14 Dec 1988     Fixed bug in EGAZAP


ZAP -

 ZAP is a resident utility that blanks the screen after a specified
 period of inactivity.  The ZAP.ASM program actually generates two
 different programs depending on the assembler options:  EGAZAP and
 VGAZAP.  The first is for the IBM Enhanced Graphics Adapter or
 compatibles, and the second is for IBM PS/2's, the IBM Video Graphics
 Adpater, and comaptibles.  From here on, ZAP will be used to mean
 EGAZAP or VGAZAP, whichever is appropriate for your hardware.

 To install ZAP, simply put the command ZAP in your AUTOEXEC.BAT file.
 From then on, when there is five minutes of inactivity at the
 keyboard, ZAP will blank the screen until any key (even just a shift
 key) is hit.  The time can be changed with a command line option which
 specifies the time in seconds.  For example:

     zap 600

 will install ZAP (if not already installed) and change the time to 10
 minutes.

 You can also turn the installed ZAP on and off using ZAP.  For example:

     zap off

 will turn off the installed ZAP, so it will not blank the screen.  Then
 the command:

     zap on

 will turn ZAP back on.

 ZAP can also be installed in the "off" state, awaiting a "zap on"
 command, simply by using:

     zap off

 in AUTOEXEC.BAT.  You can also specify on or off along with a new
 inactivity time.  For example, the command:

     zap off 600

 in AUTOEXEC.BAT will install ZAP in the off state with a 10 minute
 inactivity time.  Then a subsequent "zap on" will turn it on.  The time
 must be in the range of one to 3600 seconds (one hour).  Specifying a
 new time does not change whether ZAP is enabled or not and turning ZAP
 on or off does not change the time.  Also, the two options can be in
 either order.  For example, "zap 600 off" does the same thing as the
 example above.  If ZAP is already installed, subsequent invocations of
 ZAP will not install it again.  If the command:

     zap

 is entered after ZAP is already installed, this has the same effect as
 the command "zap on", that is it turns on ZAP if it was off.

 ZAP turns the display back on not only when any key is hit, but also if
 any video BIOS calls (int 10h) are made.  Since most application
 programs seem to bypass the BIOS for video, this added feature has
 little effect.

 There are a few, rare programs that also completely take the keyboard
 from the BIOS, in which case ZAP can no longer find out when keystrokes
 occur.  An example is STSC APL (a programming language).  In this case,
 ZAP will blank your display, even though you have been merrily typing
 away for the last five minutes in the application.  And the only way to
 get the display back on is to return to DOS (assuming you can get out
 while driving the application blindfolded).  For such applications, you
 should include the commands "zap off" and "zap on" in a batch file that
 runs the application to disable ZAP before entering and enabling ZAP
 after leaving the application.  You will quickly discover if you have
 any such applications.

 This program assumes that the current display is the (only) active
 display, but does not check for it either at installation or when
 running.

 For the EGA, the screen is blanked by setting the number of characters
 displayed to one, and the start of horizontal blanking to the first
 character.  The number of displayed characters needs to be small (set
 to one for convenience) since the horizontal blanking interval is
 limited to 32 characters.  The screen is restored by getting the
 current screen mode information from the BIOS and from that and the
 table of Start Horizontal Blanking values in this program (copied from
 the BIOS listing---not entirely kosher, but the only decent approach),
 the proper register values are restored.

 For the VGA, the screen is blanked and restored using the Screen Off
 bit in the Clocking Mode Register (port 0x3c4, address 01, bit 5).

 To minimize the resident memory required, this program is assembled
 separately for the EGA or VGA.  When assembling, define the symbol EGA
 or VGA in the command line using /d (see the manual for MASM or TASM).
 If no symbol is defined, you will be warned and the resulting .COM file
 will be asssembled for the VGA.  For example, the commands:

     tasm /dega zap
     tlink /t zap,egazap
     tasm /dvga zap
     tlink /t zap,vgazap

 will generate EGAZAP.COM and VGAZAP.COM, assuming that you have the
 Borland Turbo Assembler.

 The fact that the number of bytes in VGAZAP (666) is the same as
 Reagan's retirement home's address in Bel Air should be given no
 religious significance.

#

ifndef VGA
ifndef EGA
 %out !No display specified---assembling for the VGA.
endif
endif

;
; Macros for blanking screens.
;

egaoff macro
 local ismono,CRTMON,CRTCOL
CRTMON equ 03B4h        ;;CRT controller register in Mono mode.
CRTCOL equ 03D4h        ;;CRT controller register in Color mode.
  push AX               ;;Save registers.
  push BX
  push CX
  push DX
  mov AH,12h            ;;Get Mono/Color in BH.
  mov BL,10h
  pushf                 ;;Do Int 10h
  push CS
  call altvid
  mov DX,CRTMON         ;;Point DX to CRT port in Mono mode.
  test BH,BH            ;;See if color mode.
  jnz ismono            ;;If not, then DX is correct.
   mov DX,CRTCOL        ;;If color, use color address.
 ismono:
  mov AX,1              ;;Set number of characters to 1.
  out DX,AX
  inc AX                ;;Set horizontal start of blanking to char 0.
  out DX,AX
  pop DX                ;;Restore registers.
  pop CX
  pop BX
  pop AX
endm

egaon macro
 local ismono,enhance,shbget,tbl,CRTMON,CRTCOL
CRTMON equ 03B4h        ;;CRT controller register in Mono mode.
CRTCOL equ 03D4h        ;;CRT controller register in Color mode.
;;
;; Restore the display by getting the correct register values and
;; setting them.
;;
        ;; save registers used by routine, except AX.
  push BX
  push CX
  push DX
        ;; get CRT port, switch setting.
  mov AH,12h            ;;Get switch setting into CL, Mono/Color in BH.
  mov BL,10h
  pushf                 ;;Do Int 10h
  push CS
  call altvid
  mov DX,CRTMON         ;;Point DX to CRT port in Mono mode.
  test BH,BH            ;;See if color mode.
  jnz ismono            ;;If not, then DX is correct.
   mov DX,CRTCOL        ;;If color, use color address.
 ismono:
        ;; get values for CRT registers 1 and 2.
  mov AH,0Fh            ;;Get mode into AL, columns into AH.
  pushf                 ;;Do Int 10h
  push CS
  call altvid
  dec AH                ;;Compute Horizontal Display End setting (1).
  cmp AL,3              ;;See if color mode.
  ja shbget             ;;If not, go on to get Start Horiz Blank (2).
   cmp CL,3             ;;See if in secondary enhanced mode.
   je enhance           ;;If so, use enhanced 0-3 settings.
    cmp CL,9            ;;See if in primary enhanced mode.
    jne shbget          ;;If not, use normal 0-3 settings.
   enhance:
     add AL,11h         ;;Add offset for table.
 shbget:
  mov BX,(offset trap)+(tbl-set)        ;;Point to table.
  xlat byte ptr CS:tbl  ;;Get Start Horizontal Blank setting.
        ;; Now AH is CRT register 1, AL is register 2 - set them.
  mov CL,AL             ;;Save register 2 setting.
  mov AL,1              ;;Set register 1.
  out DX,AX
  mov AH,CL             ;;Get register 2 setting.
  inc AX                ;;Set register 2.
  out DX,AX
        ;; done, restore registers and return.
  pop DX
  pop CX
  pop BX
  ret
        ;;Start horiz blank values for modes 0-10, 0*-3*.
 tbl label byte
  db 2Dh,2Dh,5Ch,5Ch,2Dh,2Dh,59h,56h            ;;0-7.
  db 2Dh,2Dh,2Dh,5Ch,56h,2Dh,59h,56h,53h        ;;8-10h.
  db 2Bh,2Bh,53h,53h                            ;;0*-3*.
endm

vgaoff macro
 local CRTSEQ
CRTSEQ equ 03C4h        ;;CRT Sequencer register set.
  push AX               ;;Save registers.
  push DX
  mov DX,CRTSeq         ;;Sequencer registers.
  mov AL,1              ;;Point to Clocking Mode register.
  out DX,AL
  inc DX
  in AL,DX              ;;Get current value.
  or AL,020h            ;;Turn on Screen Off bit.
  out DX,AL
  pop DX                ;;Restore registers.
  pop AX
endm

vgaon macro
 local CRTSEQ
CRTSEQ equ 03C4h        ;;CRT Sequencer register set.
        ;; save registers used by routine, except AX.
  push DX
        ;; turn Screen Off bit off.
  mov DX,CRTSEQ         ;;Sequencer registers.
  mov AL,1              ;;Point to Clocking Mode register.
  out DX,AL
  inc DX
  in AL,DX              ;;Get current value.
  and AL,0DFh           ;;Turn off Screen Off bit.
  out DX,AL
        ;; done, restore registers and return.
  pop DX
  ret
endm


;
; Interrupt vector segment definitions.
;

ints segment at 0
dummy label far
 org 8*4                ;Point to Int 8 (tick) vector.
int8 label word
 org 9*4                ;Point to Int 9 (scan) vector.
int9 label word
 org 10h*4              ;Point to Int 10h (video) vector.
int10 label word
ints ends


;
; Program segment.
;

zap segment
 assume CS:zap,DS:zap,ES:zap,SS:zap

;
; Put service code as low as DOS will allow.
 org 5Ch
time dw ?               ;Time before blanking in ticks.
count dw ?              ;Tick countdown.
trap label word         ;Location for interrupt traps.

;
; Partially parsed command line.
 org 5Ch
f1 db 12 dup(?)
 org 6Ch
f2 db 12 dup(?)

;
; Constants.
DTIME equ 5462          ;Default time of about five minutes.

;
; Start of .COM code - jump to installation.
 org 100h
start:
  jmp cpyrt
   db 13,'ZAP version 1.0  Copyright (C) 1988  Mark Adler',13,10
   db 'All rights reserved.',13,10,'Z'-64
 cpyrt:
 ;
        ; process arguments.
  cld                   ;This stays in effect for the whole program.
  mov onoff,1           ;Set ZAP to on.
  mov id,'Z'            ;So we don't find COM file in a buffer.
  mov BX,offset f1
  call chknon           ;See if no arg.
  je afin
   call chkoff          ;Have first arg---see if on or off.
   je do2
    call chknum         ;Not on or off---see if number.
    jz erra             ;If no number there, then bad args.
  do2:
   mov BX,offset f2
   call chknon          ;See if second arg.
   je afin
    call chkoff         ;Have second arg---see if on or off.
    je aok
     call chknum        ;Not on or off---see if number.
     jz erra            ;If no number there, then bad args.
   aok:
 afin:

        ; look to see if ZAP is installed yet.
  mov DX,DS             ;Start checking backwards from this segment.
  assume ES:nothing
 search:
   dec DX
   jz nowhere           ;If at bottom of memory, then it ain't loaded.
   mov SI,offset id     ;Point DS:SI to id string to look for.
   mov ES,DX            ;Point ES:DI to where to look.
   sub DI,DI            ;The id string should be on a 16 byte boundary.
   mov CX,idlen
   repe cmpsb
   jne search           ;If no match, look one back.
        ; now ES:DI point to byte after id.
  mov AL,onoff          ;Set enable byte of ZAP.
  stosb
  add DI,16-(1+idlen+4) ;Point to time and count.
  dec DX
  mov ES,DX
  mov AX,newtime        ;Get time setting.
  test AX,AX            ;See if it is a new setting.
  jnz usenew
   mov AX,ES:[DI]       ;If no new setting, use old setting.
 usenew:
  stosw
  stosw                 ;Reset count as well.
  mov AH,0Fh            ;Turn display on in case it's off.
  int 10h               ;(dummy int 10 call.)
  int 20h               ;Done.

        ; ZAP not installed---install with specified options.
 nowhere:
  mov AX,DS             ;Restore ES.
  mov ES,AX
  assume ES:zap
  mov AL,onoff          ;Get on/off setting.
  mov enbl,AL           ;Put in enbl flag in traps before moving.
  mov AX,newtime        ;Set time and count.
  test AX,AX
  jnz timok
   mov AX,DTIME         ;Get default time (five minuntes).
 timok:
  mov time,AX
  mov count,AX
  jmp copy              ;Go set up traps and stay resident.

erra:
  mov DX,offset err2
  jmp short errx

chknon proc near
  mov SI,BX
  mov DI,offset snone
  mov CX,6
  repe cmpsw
  ret
chknon endp

chkoff proc near
 ; Compare [BX] with soff and son, return NE if neither match.
  mov SI,BX
  mov DI,offset soff
  mov CX,6
  repe cmpsw
  jne noff
   mov onoff,0
   ret
 noff:
  mov SI,BX
  mov DI,offset son
  mov CX,6
  repe cmpsw
  ret
chkoff endp

chknum proc near
  lea SI,[BX+1]         ;Point to arg (BX loaded already).
  sub BX,BX             ;Initial value.
  mov DI,10             ;Base for decimal.
  mov CX,8              ;Digits allowed in name.
 numlp:
   lodsb
   sub AL,'0'
   jb nend
   cmp AL,9
   ja nend
   cbw
   xchg AX,BX
   mul DI
   add BX,AX
   loop numlp
 nend:
  test BX,BX            ;See if got a value.
  jz nret               ;If not, just return.
   mov AX,91            ;Multiply by 18.2.
   mul BX
   shr DI,1             ;Put 5 in DI.
   cmp DX,DI
   jae errn             ;If number of seconds too high, then error.
   div DI               ;18.2 = 91/5.
   cmp DX,3             ;See if need to round up.
   jb rdown             ;If remainder 0, 1, or 2, then round down.
    inc AX              ;Else, round up.
  rdown:
   mov newtime,AX       ;(Note, Z flag is false here.)
 nret:
  ret                   ;Return NZ if got a valid time.
chknum endp

errn:
  mov DX,offset err1
errx:
  mov AH,9
  int 21h
  int 20h

err1 db '?Seconds out of range---must be in 1..3600',13,10,'$'
err2 db '?Invalid argument---can be "on", "off", or time'
     db 10,13,'$'

soff db 0,'OFF        '
son db 0,'ON         '
snone db 0,'           '
newtime dw 0
onoff db 1

;
; Traps - only assume CS points here.
  assume DS:nothing,ES:nothing,SS:nothing
set:                    ;Traps.

 id db ' APTSR'
 idlen equ $-id
 enbl db 1              ;Enable flag.

 tick:
  ;
  ; Timer tick action - if tick count not at already at zero, decrement
  ; it.  If this makes the count zero, blank the screen.
  ;
   cmp byte ptr trap+(enbl-set),1       ;See if enabled.
   jne tfin             ;If not, skip this.
   cmp count,0          ;See if count at zero.
   je tfin              ;If so, don't decrement.
    dec count           ;Decrement tick count.
    jnz tfin            ;Wait until counts down to zero.
        ; disable display.
    ifdef EGA
     egaoff
    else
     vgaoff
    endif
        ; go on to service routine.
  tfin:
   jmp dummy            ;Go on to service routine.
  tvec equ $-4          ;Address in jmp.

 scan:
  ;
  ; Keyboard scan code action - reset the count to the maximum.  If the
  ; count was zero, then the screen is blanked.  In that case, restore
  ; the display.
  ;
   push AX
   cmp count,0          ;See if count at zero.
   jne sfin             ;If not, just reset count.
    call don            ;Display blanked - restore it.
  sfin:
   mov AX,time
   mov count,AX         ;Reset count.
   pop AX
   jmp dummy            ;Go on to service routine.
  svec equ $-4          ;Address in jmp.

 vid:
  ;
  ; Video service request action - reset the count to the maximum.  If
  ; the count was zero, then the screen is blanked.  In that case,
  ; restore the display.
  ;
   push AX
   cmp count,0          ;See if count at zero.
   jne vfin             ;If not, just reset count.
    call don            ;Display blanked - restore it.
  vfin:
   mov AX,time
   mov count,AX         ;Reset count.
   pop AX
 altvid:                ;(For using Int 10h within these routines.)
   jmp dummy            ;Go on to service routine.
  vvec equ $-4          ;Address in jmp.


 don:
  ifdef EGA
   egaon
  else
   vgaon
  endif

 setlen equ $-set       ;End of traps.


;
; Installation code - all segment registers set.
 assume DS:zap,ES:zap,SS:zap

 copy:
  ;
  ; Install traps and tell DOS to leave them in memory.
  ;
        ; copy traps to lower memory.
   mov SI,offset set
   mov DI,offset trap
   mov CX,setlen
   rep movsb            ;Assume direction flag cleared.
        ; set up to insert traps into interrupt vectors.
   sub AX,AX
   mov ES,AX            ;Point to interrupt area.
   assume ES:ints
   cli                  ;Disable interrupts during change.
        ; insert trap in timer tick interrupt vector.
   mov AX,int8          ;Get old vector.
   mov trap+(tvec-set),AX       ;Put in jump instruction.
   mov AX,int8+2
   mov trap+(tvec+2-set),AX
   mov AX,offset trap+(tick-set)
   mov int8,AX          ;Change Int 8 to the trap.
   mov AX,CS
   mov int8+2,AX
        ; insert trap in keyboard scan code interrupt vector.
   mov AX,int9          ;Get old vector.
   mov trap+(svec-set),AX       ;Put in jump instruction.
   mov AX,int9+2
   mov trap+(svec+2-set),AX
   mov AX,offset trap+(scan-set)
   mov int9,AX          ;Change Int 9 to the trap.
   mov AX,CS
   mov int9+2,AX
        ; insert trap in video service interrupt vector.
   mov AX,int10         ;Get old vector.
   mov trap+(vvec-set),AX       ;Put in jump instruction.
   mov AX,int10+2
   mov trap+(vvec+2-set),AX
   mov AX,offset trap+(vid-set)
   mov int10,AX         ;Change Int 10h to the trap.
   mov AX,CS
   mov int10+2,AX
        ; tell DOS to keep the traps in memory and exit.
   sti                  ;Interrupts OK now.
   mov DX,offset trap+setlen    ;Amount to keep.
   int 27h              ;Exit and remain resident.

zap ends

end start