f100 500 0
a100
;
;----------------------------------------
; DOSMON - DOS Activity Monitor
;----------------------------------------
;
; This program will terminate and stay resident.  It intercepts the
; DOS service interrupt and displays status information on the
; screen during DOS service execution periods.
;
; S.H.Smith, 15-may-86
;


a100
;----------------------------------------
; startup entry point
;----------------------------------------
   jmp 2e0       ;install


a103
; vector for old interrupt
   db 0,0,0,0


a107
; segment address for display memory
; filled in by startup code
   dw 0


a10e
; twiddle display index
   dw 0


a110
; twiddle display characters
   db "Ä\³/"


a130
; a signature in bytes
   db 0a,0d,'DOSMON - DOS Activity Monitor',0a,0d
   db '$  S.H.Smith, 15-May-86',0a,0d
   db 1a


a170
;----------------------------------------
; new DOS service interrupt
;----------------------------------------
;
   push ds
   push es
   push bx         ;save entry registers
   push ax
;
   cs:
   mov ax,[107]    ;get display segment into es
   mov es,ax
;
;----------------------------------------
; prepare display with blanks
;
   mov ax,0f20     ;space with attribute of 15
   es:
   mov [94],ax
   es:
   mov [96],ax     ;set attribute of the function code locations
   es:
   mov [98],ax
;
;----------------------------------------
; display the rotating twiddle character
;
   cs:
   mov bx,[10e]    ;get twiddle index
   inc bx
   mov al,bl       ;advance to next twiddle position
   and al,3        ;bx=bx mod 4 to rotate through twiddles
   mov bl,al
   cs:
   mov [10e],bx    ;save next twiddle index
;
   cs:
   mov ah,[110+bx] ;get the next twiddle character
   es:
   mov [94],ah     ;put twiddle status on screen
;
;----------------------------------------
; display the DOS service number in hex
;
   pop ax          ;get the dos function code into ah
   push ax
;
   and ah,0f
   add ah,30       ;convert low digit to hex
;
   cmp ah,3a       ;handle A..F
   jb 1e8
   add ah,7
   jmp 1e8


a1e8
   es:
   mov [98],ah     ;and set LSB on screen
;
   pop ax          ;get fresh copy of function code into ah
   push ax
;
   shr ah,1        ;move down bits for high digit
   shr ah,1
   shr ah,1
   shr ah,1        ;make high byte hex and put on screen
   and ah,0f
   add ah,30
;
   cmp ah,3a       ;handle A..F
   jb 218
   add ah,7
   jmp 218


a218
   es:
   mov [96],ah     ;set MSB on screen
   jmp 228


a228
;----------------------------------------
; perform the DOS service function
;
   pop ax
   pop bx
   pop es          ;restore initial entry registers
   pop ds
;
   cs:
   jmp far [103]   ;jump to the real dos handler


a2e0
;----------------------------------------
; startup code
;----------------------------------------
; determine where the video ram is.  this is done by putting a special
; character on the screen and then looking for it in the various video
; ram locations.
;
   push cs
   pop ds
;
   mov ah,3         ;get cursor position
   int 10           ;video bios service
   push ax
   push bx
   push dx          ;save it for later
;
   mov dx,0
   mov ah,2         ;home the cursor
   int 10
;
   mov ah,0A
   mov al,88        ;display a funny char at cursor
   mov cx,1
   int 10
;
; move cursor back to original position
;
   pop dx
   pop bx
   pop ax
   mov ah,2
   int 10
;
; look for MONO video ram
;
   mov dl,88
   mov ax,b000
   mov es,ax
   es:
   cmp dl,[0]
   jz 360
;
; look for COLOR video ram
;
   mov ax,b800
   mov es,ax
   es:
   cmp dl,[0]
   jz 360
;
; couldn't find video ram; display a message and abort
;
   mov dx,308
   mov ah,9
   int 21           ;display error message
   int 20           ;terminate program


a328
   db "ERROR: Can't find display memory$"


a360
;
   cs:
   mov [107],ax     ;set the display segment
;
;----------------------------------------
; display the program signon message now that we are sure
; that we can be installed
;
   mov dx,130
   mov ah,9
   int 21           ;display signon message
;
;----------------------------------------
; now install new interrupt handler
;
   mov ax,0
   mov es,ax
;
; save old DOS service vector
;
   es:
   mov ax,[84]
   cs:
   mov [103],ax
;
   es:
   mov ax,[86]
   cs:
   mov [105],ax
;
; install new vector
;
   mov ax,170       ;entry point offset
   es:
   mov [84],ax
;
   mov ax,cs        ;this code segment
   es:
   mov [86],ax
;
; set last resident code offset
; and terminate-and-stay-resident
;
   mov al,0         ;exit code
   mov dx,30        ;paragraphs to keep resident
   mov ah,31        ;keep process function
   int 21           ;terminate and stay in memory


rcx
400
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