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| ; |
| ; WORK IN PROGRESS TEMPLATE! NOT USED YET |
| ; |
| ; int 24h handler, part of SvarCOM. MIT license. |
| ; Copyright (C) 2022 Mateusz Viste |
| ; |
| ; 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. |
| ; |
| |
| org 0 ; this code does not have a PSP, it is loaded as-is into a memory |
| ; segment |
| |
| ; === 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 happenned) |
| ; 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 |
| ; ============================================================================= |
| |
| |
| ; save registers so I can restore them later |
| push ah |
| push bx |
| push cx |
| push dx |
| pushf |
| |
| ; 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 dx |
| pop cx |
| pop bx |
| pop ah |
| |
| iret |
| |
| |
| ; write DX string to stderr |
| write_dx_str_to_stderr: |
| push ax |
| push bx |
| push cx |
| |
| mov ah, 0x40 ; write to file -- am I sure I can use this function safely? |
| mov bx, 2 ; stderr |
| mov cx, 1 ; one byte |
| int 0x21 |
| |
| pop cx |
| pop bx |
| pop ax |