; Subroutine to test for INT13 Extensions

7CAA B441          MOV     AH,41        ; Function 41h of INT 13:
7CAC BBAA55        MOV     BX,55AA      ; (with BX = 55AAh) is a check for
                                        ;  the "Installation of the INT 13
                                        ;  BIOS Extensions" in Memory.
7CAF 8A162400      MOV     DL,[0024]    ; -> 80h (for First drive).
7CB3 CD13          INT     13

7CB5 720F          JB      7CC6             ; Return
7CB7 81FB55AA      CMP     BX,AA55
7CBB 7509          JNZ     7CC6             ; Return
7CBD F6C101        TEST    CL,01
7CC0 7404          JZ      7CC6             ; Return
7CC2 FE061400      INC     BYTE PTR [0014]
7CC6 C3            RET

; Subroutine to Read all 16 Sectors of Boot Code into Memory

7CC7 6660        * pushad           ; Push all "Double" Registers onto the
                                    ;  stack: EAX, ECX, EDX, EBX, original
                                    ;         ESP, EBP, ESI, and EDI.
7CC9 1E            PUSH    DS
7CCA 06            PUSH    ES
7CCB 66A11000    * mov     eax,[0010] ; "Must always be zero for NTFS!"
7CCF 6603061C00  * add     eax,[001C] ;  Number of "Hidden Sectors"
7CD4 663B062000  * cmp     eax,[0020] ;  Apparent Sectors in partition.
7CD9 0F823A00    * jb      7D17       ;  Can't have more "Hidden Sectors"
                                      ;   than the total you start with!
7CDD 1E            PUSH    DS
7CDE 666A00      * push    00000000
7CE1 6650        * push    eax
7CE3 06            PUSH    ES
7CE4 53            PUSH    BX
7CE5 6668100001  * push    00010010
     00
7CEB 803E140000    CMP     BYTE PTR [0014],00
7CF0 0F850C00    * jnz     7D00
7CF4 E8B3FF        CALL    7CAA         ; Check for Extended INT13 code.
7CF7 803E140000    CMP     BYTE PTR [0014],00
7CFC 0F846100    * jz      7D61         ; Extensions are not installed.
                                        ; -> "A disk read error..." etc.

7D00 B442          MOV     AH,42        ; Function 42h of INT 13:
                                        ;    " Extended Read "
7D02 8A162400      MOV     DL,[0024]    ; -> "80h" (first hard drive).
7D06 16            PUSH    SS
7D07 1F            POP     DS
7D08 8BF4          MOV     SI,SP
7D0A CD13          INT     13

7D0C 6658        * pop     eax
7D0E 5B            POP     BX
7D0F 07            POP     ES
7D10 6658        * pop     eax
7D12 6658        * pop     eax
7D14 1F            POP     DS
7D15 EB2D          JMP     7D44

7D17 6633D2      * xor     edx,edx
7D1A 660FB70E18  * movzx   ecx,word [0018]  ; [7C18] = Sectors per Track
     00
7D20 66F7F1      * div     ecx
7D23 FEC2          INC     DL
7D25 8ACA          MOV     CL,DL
7D27 668BD0      * mov     edx,eax
7D2A 66C1EA10    * shr     edx,10
7D2E F7361A00    * div     word [001A]   ; [7C1A] = Number of Heads
7D32 86D6          XCHG    DL,DH
7D34 8A162400      MOV     DL,[0024]     ; [7C24] = Hard Drive Number
7D38 8AE8          MOV     CH,AL
7D3A C0E406      * shl     ah,06
7D3D 0ACC          OR      CL,AH
7D3F B80102        MOV     AX,0201       ; Function 02h of INT 13:
7D42 CD13          INT     13            ; "Read Sector into Memory"

7D44 0F821900    * jb      7D61          ; -> "A disk read error..." etc.
7D48 8CC0          MOV     AX,ES
7D4A 052000        ADD     AX,0020       ; Add another 200h (512 bytes) to
7D4D 8EC0          MOV     ES,AX         ;    the Segment pointer in ES.
7D4F 66FF061000  * inc     dword [0010]    ; 
7D54 FF0E0E00      DEC     WORD PTR [000E] ; Decrement the Count of how
                                           ; many Sectors are left to read
7D58 0F856FFF    * jnz     7CCB
7D5C 07            POP     ES
7D5D 1F            POP     DS
7D5E 6661        * popad
7D60 C3            RET

--------------------------------------------------------------------------------

7D61 A0F801        MOV     AL,[01F8]   ; Contains 83h (for all Languages)
                                       ; -> "A disk read error occurred"
7D64 E80900        CALL    7D70        ; DISPLAY MESSAGE
7D67 A0FB01        MOV     AL,[01FB]   ; Contains C9h (for English).
                                       ; -> "Press Ctrl+Alt+Del to restart"
7D6A E80300        CALL    7D70        ; DISPLAY MESSAGE
7D6D FB            STI
7D6E EBFE          JMP     7D6E        ; Endless Loop -> Lock-up System,
                                       ;       so a reboot is necessary!

7D70 B401          MOV     AH,01       ; An alternate method to add 100h to
                                       ; the AX register for the Message 
7D72 8BF0          MOV     SI,AX       ; Offsets in AL -> Error Messages.
7D74 AC            LODSB               ; Load Error Message strings 1 byte
                                       ;    at a time and INC SI pointer.
7D75 3C00          CMP     AL,00       ; Look for Zero-byte terminator in
                                       ;    the Error Message strings.
7D77 7409          JZ      7D82        ; Return (done)
7D79 B40E          MOV     AH,0E       ; Function 0Eh of INT 10:
                                       ; "Teletype Output" (One Character)
7D7B BB0700        MOV     BX,0007     ; (BH=Page Zero; BL=Normal display)
7D7E CD10          INT     10
7D80 EBF2          JMP 7D74            ; Do it all over again . . .
7D82 C3            RET

; Subroutine to Read all 16 Sectors of Boot Code into Memory

7CC7 6660        * pushad           ; Push all "Double" Registers onto the
                                    ;  stack: EAX, ECX, EDX, EBX, original
                                    ;         ESP, EBP, ESI, and EDI.
7CC9 1E            PUSH    DS
7CCA 06            PUSH    ES
7CCB 66A11000    * mov     eax,[0010] ; "Must always be zero for NTFS!"
7CCF 6603061C00  * add     eax,[001C] ;  Number of "Hidden Sectors"
7CD4 663B062000  * cmp     eax,[0020] ;  Apparent Sectors in partition.
7CD9 0F823A00    * jb      7D17       ;  Can't have more "Hidden Sectors"
                                      ;   than the total you start with!
7CDD 1E            PUSH    DS
7CDE 666A00      * push    00000000
7CE1 6650        * push    eax
7CE3 06            PUSH    ES
7CE4 53            PUSH    BX
7CE5 6668100001  * push    00010010
     00
7CEB 803E140000    CMP     BYTE PTR [0014],00
7CF0 0F850C00    * jnz     7D00
7CF4 E8B3FF        CALL    7CAA         ; Check for Extended INT13 code.
7CF7 803E140000    CMP     BYTE PTR [0014],00
7CFC 0F846100    * jz      7D61         ; Extensions are not installed.
                                        ; -> "A disk read error..." etc.

7D00 B442          MOV     AH,42        ; Function 42h of INT 13:
                                        ;    " Extended Read "
7D02 8A162400      MOV     DL,[0024]    ; -> "80h" (first hard drive).
7D06 16            PUSH    SS
7D07 1F            POP     DS
7D08 8BF4          MOV     SI,SP
7D0A CD13          INT     13

7D0C 6658        * pop     eax
7D0E 5B            POP     BX
7D0F 07            POP     ES
7D10 6658        * pop     eax
7D12 6658        * pop     eax
7D14 1F            POP     DS
7D15 EB2D          JMP     7D44

7D17 6633D2      * xor     edx,edx
7D1A 660FB70E18  * movzx   ecx,word [0018]  ; [7C18] = Sectors per Track
     00
7D20 66F7F1      * div     ecx
7D23 FEC2          INC     DL
7D25 8ACA          MOV     CL,DL
7D27 668BD0      * mov     edx,eax
7D2A 66C1EA10    * shr     edx,10
7D2E F7361A00    * div     word [001A]   ; [7C1A] = Number of Heads
7D32 86D6          XCHG    DL,DH
7D34 8A162400      MOV     DL,[0024]     ; [7C24] = Hard Drive Number
7D38 8AE8          MOV     CH,AL
7D3A C0E406      * shl     ah,06
7D3D 0ACC          OR      CL,AH
7D3F B80102        MOV     AX,0201       ; Function 02h of INT 13:
7D42 CD13          INT     13            ; "Read Sector into Memory"

7D44 0F821900    * jb      7D61          ; -> "A disk read error..." etc.
7D48 8CC0          MOV     AX,ES
7D4A 052000        ADD     AX,0020       ; Add another 200h (512 bytes) to
7D4D 8EC0          MOV     ES,AX         ;    the Segment pointer in ES.
7D4F 66FF061000  * inc     dword [0010]    ; 
7D54 FF0E0E00      DEC     WORD PTR [000E] ; Decrement the Count of how
                                           ; many Sectors are left to read
7D58 0F856FFF    * jnz     7CCB
7D5C 07            POP     ES
7D5D 1F            POP     DS
7D5E 6661        * popad
7D60 C3            RET

--------------------------------------------------------------------------------

7D61 A0F801        MOV     AL,[01F8]   ; Contains 83h (for all Languages)
                                       ; -> "A disk read error occurred"
7D64 E80900        CALL    7D70        ; DISPLAY MESSAGE
7D67 A0FB01        MOV     AL,[01FB]   ; Contains C9h (for English).
                                       ; -> "Press Ctrl+Alt+Del to restart"
7D6A E80300        CALL    7D70        ; DISPLAY MESSAGE
7D6D FB            STI
7D6E EBFE          JMP     7D6E        ; Endless Loop -> Lock-up System,
                                       ;       so a reboot is necessary!

7D70 B401          MOV     AH,01       ; An alternate method to add 100h to
                                       ; the AX register for the Message 
7D72 8BF0          MOV     SI,AX       ; Offsets in AL -> Error Messages.
7D74 AC            LODSB               ; Load Error Message strings 1 byte
                                       ;    at a time and INC SI pointer.
7D75 3C00          CMP     AL,00       ; Look for Zero-byte terminator in
                                       ;    the Error Message strings.
7D77 7409          JZ      7D82        ; Return (done)
7D79 B40E          MOV     AH,0E       ; Function 0Eh of INT 10:
                                       ; "Teletype Output" (One Character)
7D7B BB0700        MOV     BX,0007     ; (BH=Page Zero; BL=Normal display)
7D7E CD10          INT     10
7D80 EBF2          JMP 7D74            ; Do it all over again . . .
7D82 C3            RET

mainEntryPoint:

	mov	BS.bsDriveNumber, dl

	;=----------------------------------------------------------=
	; Load entire FAT (maximum 6KB for FAT12)
	;=----------------------------------------------------------=

	push	ax		; ax = "load" segment

	mov	ax, BPB.bpbBytesPerSector
	mov	cx, BPB.bpbSectorsPerFAT
	mul	cx

	shr	ax, 4		; convert to paragraphs

	mov	di, ss		;
	sub	di, ax		; es = di = FAT buffer
	mov	es, di		;

	mov	ax, BPB.bpbReservedSectors
	call	int13ReadSector

	pop	es		; es = "load" segment

	;=----------------------------------------------------------=
	; Load entire Root Directory (maximum 16KB for FAT12/FAT16)
	;=----------------------------------------------------------=

	mov	ax, 32
	mov	si, BPB.bpbRootEntries
	mul	si
	div	BPB.bpbBytesPerSector

	xchg	ax, cx		; cx = root sectors, ax = zero

	mov	al, BPB.bpbNumberOfFATs
	mul	BPB.bpbSectorsPerFAT

	add	ax, BPB.bpbReservedSectors
	call	int13ReadSector

	push	dx		; mzldrDataAreaHi
	push	ax		; mzldrDataAreaLo
	push	di		; mzldrFATSegment	
	push	es		; mzldrBufSegment

	;=----------------------------------------------------------=
	; Look through list of "images" and load the first match
	;=----------------------------------------------------------=

	xchg	ax, si		; ax = root entries

	mov	si, OFFSET szImageListDef


;---------------------------------------------------------------------------
;	fat12ReadCluster
;
;	Entry:
;		ch = 0
;	      	si = cluster number to read
;		es = segment of read buffer
;	Exit:
;	      	si = next cluster number in chain (if CF == 0)
;		es = next segment
;
fat12ReadCluster PROC NEAR

	lea	ax, [si-2]

	; cx = sectors per cluster

	mov	cl, BPB.bpbSectorsPerCluster
	mul	cx	

	; add start of dataarea

	add	ax, VAR.mzldrDataAreaLo
	adc	dx, VAR.mzldrDataAreaHi

	call	int13ReadSector

	shr	bx, 4		; convert bytes into paragraphs

	mov	ax, es		; ax = our buffer
	add	ax, bx		; ax = old buffer + bytes read
	mov	es, ax		; es = new buffer

	mov	ds, VAR.mzldrFATSegment

	mov	ax, 3		;
	mul	si		; ax = si * 3 / 2
	shr	ax, 1		;

	xchg	ax, si		;

	mov	si, ds:[si]	; get next cluster

	jnc	fat12ReadClusterEven

	shr	si, 4		; keep upper 4 bits

fat12ReadClusterEven:
	and	si, 0FFFh	; mask off junk, EOF?
	cmp	si, FAT12_EOF	;
	cmc
	ret

fat12ReadCluster ENDP






;---------------------------------------------------------------------------
;	int13ReadSector
;
;	Entry:
;		ax = sector number (16-bit LBA)
;		cx = sector count
;		es = sector buffer segment
;	Exit:
;		bx = number of bytes read
;	     	cx = zero
;	     dx:ax = sector number (32-bit LBA) of next sector
;
int13ReadSector PROC NEAR

	push	di

	xor	bx, bx
	xor	dx, dx

int13ReadNext:
	mov	di, 5		; five retries

int13ReadMore:
	pusha

	; add start of partition (harddisks only)

	add	ax, WORD PTR BPB.bpbHiddenSectors[0]
	adc	dx, WORD PTR BPB.bpbHiddenSectors[2]

	xor	cx, cx		; cx = null

	xchg	ax, cx		; ax = null, cx = LBA[0]
	xchg	ax, dx		; ax = LBA[2], dx = null

	div	BPB.bpbSectorsPerTrack

	xchg	ax, cx		; ax = LBA[0], cx = Result[2]

	div	BPB.bpbSectorsPerTrack

	xchg	dx, cx		; dx = Result[2], cx = Sector#
	inc	cx		; cx = one-based Sector#

	div	BPB.bpbHeadsPerCylinder

	mov	ch, al		; ch = Cylinder# [7:0]
	shl	ah, 6		; ah = Cylinder# [9:8]
	or	cl, ah		; combine Cylinder & Sector fields

	mov	dh, dl		; dh = Head#

	mov	dl, BS.bsDriveNumber

	mov	ax, 0201h
	int	13h
	jnc	int13ReadDone

;*	mov	ah, 00h		; uncomment if you want DISK RESETs
;*	int	13h		;

	popa

	dec	di
	jnz	int13ReadMore

	int	18h		;*

int13ReadDone:
	popa

	add	bx, BPB.bpbBytesPerSector

	inc	ax
	jnz	int13ReadSkip
	inc	dx

int13ReadSkip:
	dec	cx
	jnz	int13ReadNext

	pop	di
	ret

int13ReadSector ENDP

; MBR code

bootSegment SEGMENT USE16 'boot'

	ASSUME	cs:bootSegment, ds:bootSegment

	cld

	xor	ax, ax
	mov	ss, ax
	mov	sp, 7C00h

	mov	ds, ax
	mov	es, ax

	; relocate ourself down to 0060:0000

	mov	cx, 0100h
	mov	si, 7C00h
	mov	di, 0600h
	rep	movsw

	JMPF	0060h, bootEntryPoint

bootEntryPoint:

	push	cs
	pop	ds

	mov	mbrBootDrive, dl

	test	BYTE PTR es:[417h], 08h
	jnz	findPartitionMain

	mov	ax, 020Fh
	mov	bx, 0800h
	mov	cx, 0002h
	mov	dx, 0080h
	int	13h

	cmp	extMagicTag, 0AA55BEEFh	
	jne	findPartitionMain

	JMPF	0060h, 0200h

findPartitionMain:
	mov	cl, 4
	mov	si, OFFSET mbrPTable

findPartitionNext:
;*	test	[si].mbrBootFlag, MBR_ENTRY_BOOTABLE
	cmp	[si].mbrBootFlag, ch
	jl	findPartitionDone

	add	si, SIZE MBR_ENTRY
	loop	findPartitionNext

	int	18h

findPartitionDone:
	mov	cx, [si][2]
	mov	dx, [si]

	cmp	dh, 0FFh
	jne	findPartitionNorm

	cmp	cx, 0FFFFh
	jne	findPartitionNorm

	push	LARGE NULL
	push	[si].mbrPartitionStart
	push	es
	push	bx
	push	SMALL 1
	push	SMALL 16

	push	ss
	pop	ds

	mov	si, sp

	mov	ah, 42h
	int	13h

	add	sp, 16
	jmp	findPartitionExec

findPartitionNorm:
	mov	ax, 0201h
	mov	bx, 7C00h
	int	13h

findPartitionExec:
	JMPF	0000h, 7C00h

mbrBootDrive	DB	?

	MBR_TABLE_HERE

mbrPTable MBR_ENTRY 4 DUP (<>)

	MBR_MAGIC_HERE

	push	0B800h
	pop	es

	mov	ax, 1720h
	mov	cx, 2000
	xor	di, di
	rep	stosw

	push	0
	pop	es

	mov	ah, 02h
	mov	bh, 00h
	xor	dx, dx
	int	10h

	jmp	findPartitionMain

extMagicTag EQU DWORD PTR ds:[EXT_MAGIC_POS]
	EXT_MAGIC_HERE

bootSegment ENDS

; DOS code

codeSegment SEGMENT USE16 'code'

	ASSUME	cs:codeSegment, ds:codeSegment

mainEntryPoint:

	push	cs
	pop	ds

	push	cs
	pop	es

	mov	ax, 0201h
	mov	bx, OFFSET ourSectorBuf
	mov	cx, 0001h
	mov	dx, 0080h
	int	13h

	push	bootSegment
	pop	es

	mov	si, MBR_TABLE_POS + OFFSET ourSectorBuf
	mov	di, MBR_TABLE_POS
	mov	cx, 32
	rep	movsw

	mov	ax, 0302h
	xor	bx, bx
	mov	cx, 1
	mov	dx, 0080h
	int	13h

	mov	ax, 4C00h
	int	21h

ourSectorBuf DB 512 DUP (?)

codeSegment ENDS

	END	mainEntryPoint