source: xtideuniversalbios/trunk/XTIDE_Universal_BIOS/Src/Handlers/Int13hMFMcompatibility.asm @ 594

; Project name  :   XTIDE Universal BIOS
; Description   :   Int 13h handler that is used by MODULE_MFM_COMPATIBILITY.
;                   It is placed between XTUB Int 13h hander and system INT 13h hander
;                   to hide XTUB from MFM controllers whose BIOS assumes they handler
;                   all hard drives on the system.

;
; XTIDE Universal BIOS and Associated Tools
; Copyright (C) 2009-2010 by Tomi Tilli, 2011-2013 by XTIDE Universal BIOS Team.
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation; either version 2 of the License, or
; (at your option) any later version.
;
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
; GNU General Public License for more details.
; Visit http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
;

; Section containing code
SECTION .text


;--------------------------------------------------------------------
; Int 13h software interrupt handler for MFM compatibility.
;
; Some MDM controllers require that BDA drive count is what they have set.
; The purpose for this handler is to restore BDA drive count to what MFM controller
; expects and then call MFM controller INT 13h.
;
; Int13hMFMcompatibilityHandler
;   Parameters:
;       Any INT 13h function and parameters
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
Int13hMFMcompatibilityHandler:
    eENTER  6, 0
    push    es
    push    ds
    push    di

    LOAD_BDA_SEGMENT_TO es, di
    call    RamVars_GetSegmentToDS

    ; Remove our drives from BDA drive count
    push    ax
    mov     al, [RAMVARS.bDrvCnt]
    mov     [bp-2], al          ; Store our drive count for later use
    sub     [es:HDBDA.bHDCount], al
    pop     ax

    ; Copy MFM controller INT 13h address to stack
    les     di, [RAMVARS.fpMFMint13h]
    mov     [bp-4], es
    mov     [bp-6], di

    ; Restore registers so we can call MFM int 13h
    pop     di
    pop     ds
    pop     es

    pushf   ; Push flags to simulate INT
    call far [bp-6]

    ; Now we can restore BDA drive count
    push    ds
    push    ax
    lahf                    ; Get return flags to AH
    mov     [bp-12], ah     ; Store return flags to be popped by iret
    LOAD_BDA_SEGMENT_TO ds, ax
    mov     al, [bp-2]
    add     [HDBDA.bHDCount], al
    pop     ax
    pop     ds

    ; Return from this handler
    eLEAVE
    iret