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BIOSSEG	EQU 07C0H
BOOTSEG	EQU 0AE0H
LOADSEG	EQU 0050H

; ...
;
; Copy boot-sector to higher memory.
;

BEGLDR:
	MOV  AX, BOOTSEG
	MOV  ES, AX
	CLI		; clear maskable interrupts
	MOV  SS, AX
	MOV  SP, 1024
	STI		; restore interrupts
	PUSH WORD BIOSSEG
	POP  DS
	MOV  CX, 512
	XOR  SI, SI	; DS:SI should be 07C0:0
	XOR  DI, DI	; ES:DI should be 0AE0:0
	CLD
	REP  MOVSB

; DS:SI = 07C0:0 ... 07C0:1FF
; ES:DI = 0AE0:0 ... 0AE0:1FF

SAVSRS:
	PUSH ES		; We no longer need ES, so
	POP  DS		; DS now becomes 0AE0.
RSTCPU:
	PUSH BOOTSEG
	PUSH WORD FNDFLE
	RETF


;
; DISKERROR:	Display and error message, and
;		and await a system reset.
;

DSKERR:
	LEA  SI, [ERRMSG]
PRNSTR:
	LODSB
	OR   AL, 0
	JZ   SHORT DSKHLT
	MOV  AH, 14
	MOV  BL, 0
	JMP  SHORT PRNSTR
DSKHLT:
        XOR  AX, AX	; ! 'Restart' the PC-BIOS. !
        INT  22		; 16H
        INT  25		; 19H

;
; FINDFILE:	Search for the files 'IO.SYS'
;		and 'RMDOS.SYS'.
;
; Read the Root Directory into memory:
;

FNDFLE:
	MOV  AH, 14
	MOV  AL, '2'
	INT  16
	JMP  SHORT $
...

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BIOSSEG	EQU 07C0H	; where the PC-BIOS reads the boot-sector.
BOOTSEG	EQU 0AE0H	; the segment where the boot-sector is relocated.
LOADSEG	EQU 0050H	; where the real-mode DOS system is read. 

	USE16
	ORG 7C00H

        JMP  SHORT BEGLDR
        NOP
BPBBEG:
	DB "PEDOS1.0"
BYPRSC:	DW 512
SCPRCL:	DB 1
RVSCCN:	DW 1
FATCNT:	DB 2
RDECNT:	DW 224
	DW 2880
	DB 0F0H
SCPRTR:	DW 9
SCPRFT:	DW 18
TRPRCY:	DW 2
	DD 0
	DD 0
	DW 0
	DB 41
	DD 0
	DB "           "
	DB "FAT12   "
BPBEND:

;
; POSTBIOS:	Ensure that all segment registers
;		are set to known values.
;
; Copy boot-sector to higher memory.
;

BEGLDR:
	MOV  AX, BOOTSEG
	MOV  ES, AX
	CLI			; clear maskable interrupts
	MOV  SS, AX
	MOV  SP, 1024
	STI			; restore interrupts
	PUSH WORD BIOSSEG
	POP  DS
	XOR  SI, SI	; DS:SI should be 07C0:0
	XOR  DI, DI	; ES:DI should be 0AE0:0
	MOV  CX, 256
	CLD
	REP  MOVSW

; DS:SI = 07C0:0 ... 07C0:1FF
; ES:DI = 0AE0:0 ... 0AE0:1FF

SAVSRS:
	PUSH ES		; We no longer need ES, so
	POP  DS		; DS now becomes 0AE0.
RSTCPU:
	PUSH BOOTSEG
	PUSH WORD DSKERR
	RETF		; 0000:AE00+<FNDFLE>


;
; DISKERROR:	Display and error message, and
;		and await a system reset.
;

DSKERR:
	LEA  SI, [ERRMSG]
PRNSTR:
	LODSB
	OR   AL, 0
	JZ   SHORT DSKHLT
	MOV  AH, 14
	MOV  BL, 0
	JMP  SHORT PRNSTR
DSKHLT:
        XOR  AX, AX	; ! 'Restart' the PC-BIOS. !
        INT  22		; 16H
        INT  25		; 19H

;
; FINDFILE:	Search for the files 'IO.SYS'
;		and 'RMDOS.SYS'.
;
; Read the Root Directory into memory:
;

FNDFLE:
	MOV  BX, 7
	MOV  AH, 14
	MOV  AL, '2'
	INT  16
	JMP  SHORT $
	
	MOV  AX, 19
	LEA  BX, [DSKBUF]	; BX=7E00
	MOV  CX, 1
	XOR  DX, DX
	ADC  DX, 0
FNDSYS:
	JNE  DSKERR
FDNDOS:
	JNE  DSKERR


;
; READFILE:	Partially read the file
;		'IO.SYS' into memory.
;
; Read the FAT into memory:
;

REDFLE:
NXTCLU:
CLUODD:
REDNXT:
	JMP  NXTCLU

; Transfer CPU execution to io.sys
;
RUNDOS:
        PUSH  CS
        PUSH  WORD LOADSEG
	RETF


;
; REDSEC: Read the specified sectors into memory
;         at logical address ES:BX.
;
; IN:
;
; DX:AX	= head, track, sector value
; CX	= sector count
;

REDSEC:
	PUSHA
        DIV  WORD [SCPRTR]
        MOV  CX, DX
        INC  CX
        XOR  DX, DX
        DIV  WORD [TRPRCY]
        MOV  CH, AL
        SHL  AH, 6
        OR   CL, AH
        MOV  DH, DL
        MOV  DL, 0
        MOV  AX, 201H
        INT  19		; 13H
        JNC  SHORT NXTSEC
        JMP  DSKERR
NXTSEC:
        POPA
	DEC  CX
	JZ   SHORT SR1RET
	ADD  BX, WORD [BYPRSC]
	ADD  AX, 1
	ADC  DX, 0
	JMP  SHORT REDSEC
SR1RET:
        RET


; error message
ERRMSG:	DB "Non-System disk or disk error... Replace and try again when ready."
	DB 0

DOSFLE:	DB "RMDOS   SYS" ; The real-mode kernel component to PE-DOS.
SYSFLE:	DB "IO      SYS" ; I/O system. 
	
	TIMES 510 - ($ - $$) DB 0
        DW 0AA55H	; End of Boot Sector.
DSKBUF:

;
; The FAT and Root-Dir is read exactly
; after the boot-sector.
;

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ORG 7C00H

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ORG 7C00H

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ORG 0AE00H

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ORG 0

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ORG 7C0H

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ORG 0AE0H

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ORG 0

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// no org

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   PUSH WORD BIOSSEG
   POP  DS

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RSTCPU:
   PUSH BOOTSEG
   PUSH WORD FNDFLE
   RETF