Assembly Source series of Dskwatch

This is the past DOS era of the compilation of source code, although has passed, but for the study of the assembly is still helpful, assembly language is just a basic programmer language, most people can grasp, not necessarily in-depth research.

; by Steve Holzner (from June 1985 issue of PC Magazine)
Interrupts segment at 0h; This is where the disk interrupt
ORG 13h*4; Holds the address of its service routine
Disk_int label DWORD
Interrupts ends
Screen segment at 0b000h; A dummy segment to use as the Extra
Screen ends; Segment so we can write to the display
CODE_SEG segment
Assume Cs:code_seg
ORG 0100h; ORG = 100h to make this a. COM file
FIRST:JMP Load_watch; The through jump to initialize routine
Msg_part_1 db ' Disk error: '; Here are the error messages
Msg_part_2 db ' No response Failed seek NEC Error '
DB ' Bad CRC SEENDMA overrun impos Sector '
DB ' No Addr markw. Protectederr Unknown '
First_position DW? ; Position of 1st char on screen
Flags DW?
Screen_seg_offset DW 0; 0 for Mono, 8000h for graphics
Old_disk_int DD? ; Location of old disk interrupt
Ret_addr label DWORD; Used in fooling around with
Ret_addr_word DW 2 dup (?)　 ; The stack
Disk_watch proc far; The disk interrupt'll now come here
Assume Cs:code_seg
PUSHF; The call old disk interrupt
Call Old_disk_int
PUSHF; Save the flags in memory location "flags"
Pop flags; (Cunning name)
JC Error; If There is an error, carry flag would have
JMP fin; been set by Disk Interrupt
Error:push Ax; AH has the status of the error
Push CX; Push all used registers for politeness
Push DX
Push di
Push SI
Push ES
Lea Si,msg_part_1; Always print "Disk Error:" part.
Assume Es:screen; Use the screen as extra segment
MOV Dx,screen
MOV es,dx
MOV di,screen_seg_offset; DI'll is pointer to screen position
Add di,first_position; Add to point to desired
Call Write_to_screen; This is writes chars from [SI] to [DI]
MOV dx,80h; Initialize for later comparisons
MOV cx,7; Loop seven times
E_LOOP:CMP AH,DH; Are error code and DH the same?
Je e_found; If Yes, Error has been found
Add si,12; Point to next error message
SHR dh,1; Divide DH by 2
Loop E_loop; Keep going until matched DH = 0
CMP ah,3; Error code no even number; 3 perhaps?
Je e_found; If yes, have found the error
Add si,12; ERR unknown; Unknown error returned
E_found:call Write_to_screen; Write the error message to the screen
Pop es; Restore the Registers
Pop si
Pop di
Pop DX
Pop CX
Pop ax
Fin:pop Ret_addr_word; Fooling with the stack. We want to
Pop ret_addr_word[2]; Preserve the flags but the old flags
Add sp,2; are still on the stack. The I-remove
Push flags; Return address, then flags. Fill Flags
Popf; From ' FLAGS ', return to correct addr.
JMP ret_addr
Disk_watch ENDP
Write_to_screen proc near; Puts Characters on screen
MOV cx,12; Loop Times
W_loop:movs Es:byte Ptr[di],cs:[si]; Move to the screen
MOV al,7; Move screen attribute to screen buffer
MOV Es:[di],al
Inc di; Point to next byte on screen buffer
Loop W_loop; Keep going until done
Ret
Write_to_screen ENDP
Load_watch proc near; This procedure initializes everything
Assume Ds:interrupts; The data segment is the interrupt area
MOV ax,interrupts
MOV Ds,ax
MOV ax,disk_int; Get the old interrupt service routine
MOV old_disk_int,ax; Address and put it in our location
mov ax,disk_int[2]; Old_disk_int so we can call it.
MOV Old_disk_int[2],ax
mov Disk_int,offset disk_watch; Now load the address of Dskwatch
MOV Disk_int[2],cs; Routine into the disk interrupt
MOV ah,15; Ask for service INT 10h
int 10h; This tells us and display is set up
Sub ah,25; Move to twenty five places before Edge
SHL ah,1; Mult. by two (char & attribute bytes)
mov byte ptr first_position,ah; Set screen cursor
Test al,4; Is it a monochrome display?
JNZ exit; Yes-jump out
MOV screen_seg_offset,8000h; No, set up for graphics display
Exit:mov Dx,offset Load_watch; Set up Everything but I
int 27h; Stay and attach itself to DOS
Load_watch ENDP
Code_seg ends
End I; End "A" so 8088 'll go to the.