Subversion Repositories SvarDOS

; set up myself as criterr handler (int 0x24)

mov ax, 0x2524

mov dx, HANDLER_24H

int 0x21

; ****************************************************************************

; *                                                                          *

; *                                                                          *

; ****************************************************************************

;

; this is an executable image that can be set up as the critical error handler

; interrupt (int 24h). It displays the usual "Abort, retry, fail" prompt.

;

; documentation:

; http://www.techhelpmanual.com/564-int_24h__critical_error_handler.html

;

; === CRIT HANDLER DETAILS ====================================================

;

; *** ON ENTRY ***

;

; upon entry to the INT 24h handler, the registers are as follows:

;  BP:SI = addr of a "device header" that identifies the failing device

;     DI = error code in lower 8 bits (only for non-disk errors)

;     AL = drive number, but only if AH bit 7 is reset

;     AH = error flags

;        0x80 = reset if device is a disk, set otherwise

;           all the following are valid ONLY for disks (0x80 reset):

;        0x20 = set if "ignore" action allowed

;        0x10 = set if "retry" action allowed

;        0x08 = set if "fail" action allowed

;        0x06 = disk area, 0=sys files, 1=fat, 10=directory, 11=data

;        0x01 = set if failure is a write, reset if read

;

; within the int 24h handler, only these DOS functions are allowed:

;   01H-0CH (DOS character I/O)

;   33H (all subfns are OK, including 3306H get DOS version)

;   50H (set PSP address)

;   51H and 62H (query PSP address)

;   59H (get extended error information)

;

; *** ON EXIT ***

;

; After handling the error, AL should be set with an action code and get back

; to DOS. Available actions are defined in AH at entry (see above). Possible

; values on exit are:

;   AL=0  ignore error (pretend nothing happened)

;   AL=1  retry operation

;   AL=2  abort (terminates the failed program via int 23h, like ctrl+break)

;   AL=3  return to application indicating a failure of the DOS function

;

; A very basic "always fail" handler would be as simple as this:

;   mov al, 3

;   iret

;

; *** DOS CALLS ***

;

; Warning! Be careful about using DOS fns in your Critical Error handler.

;          With DOS 5.0+, ONLY the following fns can be called safely:

;

;          01H-0CH (DOS character I/O)

;          33H (all subfns are OK, including 3306H get DOS version)

;          50H (set PSP address)

;          51H and 62H (query PSP address)

;          59H (get extended error information)

;

; =============================================================================

HANDLER_24H:    ; +46Ch

; save registers so I can restore them later

push ax

push bx

push cx

push dx

push ds

pushf

; set DS to myself

push cs

pop ds

; is this a DISK error?

;test ah, 0x80

;jz DISKERROR

; non-disk error: output "CRITICAL ERROR #XXX SYSTEM HALTED" and freeze

; update the crit string so it contains the proper error code

mov bx, CRITERR

mov ax, di

xor ah, ah

mov cl, 100

div cl ; AL = AX / cl     AH = remainder

add al, '0'

mov [bx+16], al

mov al, ah

xor ah, ah

mov cl, 10

div cl

add al, '0'

add ah, '0'

mov [bx+17], al

mov [bx+18], ah

; display the string

mov ah, 0x09

mov dx, CRITERR

int 0x21

; freeze the system

HALT:

sti

hlt;

jmp HALT

DISKERROR:

; disk errors product this message:

; CRITICAL ERROR - DRIVE A: - READ|WRITE FAILURE

; (A)bort, (R)etry, (F)ail

;

; non-disk errors produce this:

; CRITICAL ERROR #errno

; restore registers and quit the handler

popf

pop ds

pop dx

pop cx

pop bx

pop ax

iret

CRITERR db "CRITICAL ERROR #XXX SYSTEM HALTED$"