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Assembly Source File | 1988-11-20 | 15.0 KB | 447 lines

title CTLT - Control-T Interrupt Handler page 60,132 ;*********************************************************************** ; ; This routine works by trapping every interrupt 9 (KB_INT) generated by ; the keyboard and handled by the IBM BIOS, and after return from BIOS, ; inspecting the key which was typed and is now present in the keyboard ; ring buffer in the BIOS data segment (40h). If it is the user ; interrupt character (normally a CTL-T), it is removed from the buffer ; and a status message is displayed on the console screen. ; ; *************** ; *** N O T E *** ; *************** ; ; This code depends upon buffer size, organization, and location, and ; pointers thereto, in the IBM BIOS data segment. If a different ; keyboard interrupt handler is installed (e.g. one that increases ; buffer size), this code will probably fail! ; ; [02-Aug-84] Nelson H.F. Beebe, College of Science Computer, ; University of Utah, Salt Lake City, UT 84112, USA ;*********************************************************************** .xlist include ascii.inc include dos.inc .list keyvect segment at 0 org 9h*4 ; BIOS KB_INT keyint label dword keyvect ends biosdata segment at 40h org 1ah ; See p. A-3 of IBM Tech. Ref. Manual buffer_head dw ? ; pointer to head of keyboard buffer ; -- address of first available char buffer_tail dw ? ; pointer to tail of keyboard buffer ; -- address of next empty slot ; -- buffer is empty if head=tail kb_buffer dw 16 dup (?) ; room for 15 entries org $-2 kb_bufend dw ? ; last word in buffer biosdata ends ;*********************************************************************** ; ; INIT_CODE - Code to load and initialize the handler. ; Sets up DOS to keep all code before "LASTONE" label safe from ; overlaying during system operation. ; ;*********************************************************************** CODE SEGMENT PARA org 100h ; for .COM file assume cs:code,ds:code assume es:biosdata TYPE_CHAR PROC NEAR ; Type character in AL at the current cursor position using the current ; character attribute. No translation is done, except that BIOS handles ; CR, LF, BEL, and BS as for a teletype. ; All registers preserved push ax push bx push ax ; save extra copy of character mov ah,$VIDEO_GETVIDEOSTATE int $VIDEO ; get current page in bh mov ah,$VIDEO_GETATTRCHAR int $VIDEO ; get current attribute in ah mov bl,ah ; save current attribute pop ax ; restore character mov ah,$VIDEO_SETTTY ; tty output (bl = current attribute) int $VIDEO ; character pop bx ; restore registers pop ax ret TYPE_CHAR ENDP assume cs:code,ds:code TYPE_CRLF PROC NEAR ; Type CR LF pair ; All registers preserved push ax ; save registers mov al,.CR call TYPE_CHAR mov al,.LF call TYPE_CHAR pop ax ; restore registers ret TYPE_CRLF ENDP assume cs:code,ds:code TYPE_DEC PROC NEAR ; Type integer in AX in decimal, BH = fill character, BL = field width ; BL=0 means minimum field width with no fill ; All registers preserved push ax ; save registers push bx push cx push dx push bp xor cx,cx mov cl,bl ; minimum field width mov bp,ax ; save original number test ax,ax ; number < 0? jge not_neg ; no neg ax ; yes, replace by abs(number) not_neg: push EFLAG ; mark end of number on stack digit_loop: cwd ; sign-extend ax into (ax,dx) dec cx ; reduce field width div TEN ; number/10 to ax, remainder to dx add dx,"0" ; convert to ASCII push dx ; save digit test ax,ax ; zero yet? ja digit_loop ; no, keep dividing mov dx,bp ; original number test dx,dx ; number < 0? jge digit_plus ; no dec cx ; yes, reduce field width cmp bh," " ; blank fill? jne digit_plus ; no mov al,"-" ; yes, save immediate leading push ax ; minus sign digit_plus: test cx,cx ; remaining count > 0? jle digit_sign ; yes, fill unnecessary mov al,bh ; fill character digit_fill: push ax ; save fill character loop digit_fill ; loop until cx=0 digit_sign: mov dx,bp ; original number test dx,dx ; number < 0? jge digit_type ; no cmp bh," " ; blank fill? je digit_type ; yes, already saved sign mov al,"-" ; no, save sign push ax digit_type: pop ax ; digit cmp ax,EFLAG ; end of number yet? je digit_done ; yes call TYPE_CHAR ; type it jmp short digit_type ; and go for next digit digit_done: pop bp ; restore registers pop dx pop cx pop bx pop ax ret ; return to caller EFLAG dw -1 ; special end-of-number flag TEN dw 10 TYPE_DEC ENDP assume cs:code,ds:code TYPE_HEX PROC NEAR ; Type byte in AL as two-character hexadecimal ; All registers preserved push cx ; save registers push bx push ax push ax ; save ax mov bh,0 ; clear top of bx mov cl,4 ; shift count mov bl,al ; byte to print shr bl,cl ; left nibble mov al,hex_chars[bx]; get character call TYPE_CHAR ; and print it pop bx ; restore ax into bx and bx,0fh ; left nibble mov al,hex_chars[bx]; get character call TYPE_CHAR ; and print it pop ax ; restore registers pop bx pop cx ret hex_chars db "0123456789ABCDEF" TYPE_HEX ENDP assume cs:code,ds:code TYPE_STRING PROC NEAR ; Type NUL-terminated string pointed to by DS:SI (the NUL is not typed). ; All registers preserved push ax push dx push si cld ; read string forward msg_loop: lodsb ; byte to al, increment si test al,al ; message byte = 0? jz done_string ; yes, all done call TYPE_CHAR ; no, type it jmp short msg_loop ; keep printing done_string: pop si pop dx pop ax ret TYPE_STRING ENDP assume cs:code,ds:code TYPE_TIME PROC NEAR ; Type the current time as hh:mm:ss ; All registers preserved push ax ; save registers push bx push cx push dx mov ah,$DOS_GETTIME int $DOS xor ah,ah ; clear top of ax mov al,ch ; hours mov bl,0 ; field width=0 mov bh," " ; fill character call TYPE_DEC ; type hh mov al,":" call TYPE_CHAR mov al,cl ; minutes mov bl,2 ; field width mov bh," " ; fill character call TYPE_DEC ; type mm mov al,":" call TYPE_CHAR mov al,dh ; seconds mov bl,2 ; field width mov bh," " ; fill character call TYPE_DEC ; type ss mov al,"." call TYPE_CHAR mov al,dl ; centiseconds mov bl,2 ; field width mov bh," " ; fill character call TYPE_DEC ; now have typed "hh:mm:ss.cc" pop dx ; restore registers pop cx pop bx pop ax ret ; return to caller TYPE_TIME ENDP assume cs:code,ds:code assume es:biosdata KEY PROC NEAR start: jmp init_code ; done only once at startup key_call: ; Far JMP to keyboard interrupt jmp far ptr es:0 ; filled in at runtime ; db 0eah ; dw 0,0 old_ip equ [bp+2] ; bp = entry_sp-2 old_cs equ [bp+4] old_fl equ [bp+6] key_rtne: sti ; turn interrupts back on push ax ; save registers push bx push cx push dx push bp push ds push es push di push si mov bx,cs mov ds,bx ; establish local DS = CS mov bx,biosdata mov es,bx ; establish ES -> BIOSDATA ; First call original KB_INT BIOS code to actually retrieve the character ; over the keyboard port and do its massive amount of bookkeeping pushf ; flags to fake interrupt call mov bx,offset key_call+1 ; get address of ROM code for keyboard call dword ptr [bx] ; call ROM code ;----------------------------------------------------------------------- ; enter critical section -- no interrupts allowed until character retrieved ; and buffer pointers updated cli ; interrupts off while char retrieved mov bx,es:buffer_tail ; next available slot in buffer dec bx ; backup 2 bytes dec bx cmp bx,offset kb_buffer ; backed up before start? jae nowrap ; no mov bx,offset kb_bufend ; yes, move to end of buffer nowrap: mov ax,es:[bx] ; char in al, scan code in ah cmp al,.ctlt ; CTL-T? jne done ; no mov es:buffer_tail,bx ; remove last character (the CTL-T) sti ; interrupts back on ; end critical section ;----------------------------------------------------------------------- call TYPE_TIME mov si,offset csip_msg call TYPE_STRING mov al,old_cs+1 call TYPE_HEX mov al,old_cs call TYPE_HEX mov al,":" call TYPE_CHAR mov al,old_ip+1 call TYPE_HEX mov al,old_ip call TYPE_HEX mov si,offset flags_msg call TYPE_STRING mov al,old_fl+1 call TYPE_HEX mov al,old_fl call TYPE_HEX call TYPE_CRLF done_int: pop si ; restore saved registers pop di pop es pop ds pop bp pop dx pop cx pop bx pop ax iret ; return from interrupt csip_msg db " CS:IP ",0 flags_msg db " Flags ",0 KEY ENDP lastone: ; all code after this label is freed to DOS after ; program initialization copyrt db 'CONTROL-T Handler -- Version 1.0 -- Public Domain 1984' db .CR,.LF db 'Nelson H.F. Beebe, University of Utah, Salt Lake City, ' db 'UT 84112, USA' db .CR,.LF,0 assume cs:code,ds:code assume es:keyvect INIT_CODE PROC NEAR ; Initialize KEYBOARD interrupt system ;----------------------------------------------------------------------- ; enter critical section -- no interrupts while adjusting interrupt vector ; cli ; interrupts off mov ax,keyvect ; Get address to interrupt vector mov es,ax ; Save in ES mov ax,es:keyint ; Get address to interrupt routine mov bx,offset key_call+1 ; Address to place to save vector mov [bx],ax ; Save interrupt address mov ax,es:keyint[2] ; Get interrupt segment for routine mov [bx+2],ax ; Save it too mov es:keyint,offset key_rtne ; Now, replace with own address mov ax,cs ; Save segment in interrupt vector mov es:keyint[2],ax sti ; interrupts back on ; end critical section ;----------------------------------------------------------------------- ; Now, print out acknowledgement to user monitor and exit mov ax,cs ; Set up segment to this routine mov ds,ax mov si,offset copyrt ; Now, print out copyright message call TYPE_STRING mov dx,offset lastone ; Save all code up to "LASTONE" label int 27h ; No return needed INIT_CODE ENDP CODE ENDS END START