%if 0

 2019, by C. Masloch

Usage of the works is permitted provided that this
instrument is retained with the works, so that any entity
that uses the works is notified of this instrument.

DISCLAIMER: THE WORKS ARE WITHOUT WARRANTY.

%endif

%include "lmacros3.mac"

	defaulting
	sectalign off

	numdef SPI, 2880	; sectors per image
	numdef CHS_SECTORS, 63	; CHS geometry field for sectors
	numdef CHS_HEADS, 255	; CHS geometry field for heads

	numdef MBR,			1
	gendef MBR_PART_TYPE,		fat12
	numdef MBR_GAP_SIZE_SECTORS,	(1024 * 1024 * 1024 * 2 * 2 - 1)

ptEmpty:		equ 0
ptFAT12:		equ 1
ptFAT16_16BIT_CHS:	equ 4
ptExtendedCHS:		equ 5
ptFAT16_CHS:		equ 6
ptFAT32_CHS:		equ 0Bh
ptFAT32:		equ 0Ch
ptFAT16:		equ 0Eh
ptExtended:		equ 0Fh
ptLinux:		equ 83h
ptExtendedLinux:	equ 85h

%if _MBR
 %ifidni _MBR_PART_TYPE,	fat12
  %assign _MBR_PART_TYPE	ptFAT12
 %elifidni _MBR_PART_TYPE,	fat16_16bit_chs
  %assign _MBR_PART_TYPE	ptFAT16_16BIT_CHS
 %elifidni _MBR_PART_TYPE,	fat16_chs
  %assign _MBR_PART_TYPE	ptFAT16_CHS
 %elifidni _MBR_PART_TYPE,	fat32_chs
  %assign _MBR_PART_TYPE	ptFAT32_CHS
 %elifidni _MBR_PART_TYPE,	fat32
  %assign _MBR_PART_TYPE	ptFAT32
 %elifidni _MBR_PART_TYPE,	fat16
  %assign _MBR_PART_TYPE	ptFAT16
 %endif
 %assign _MBR_PART_TYPE _MBR_PART_TYPE
 %ifnnum _MBR_PART_TYPE
  %error Invalid partition type specified
 %endif
 %if _MBR_PART_TYPE == 0
  %error Invalid partition type specified
 %endif
%endif


	struc PARTINFO_CHS_TUPLE
pictHead:		resb 1
pictSectorLow6:
pictCylinderHigh2:	resb 1
pictCylinderLow8:	resb 1
	endstruc

	%macro chs_tuple 1.nolist
%assign %%sector (%1) % _CHS_SECTORS
%assign %%i (%1) / _CHS_SECTORS
%assign %%head %%i % _CHS_HEADS
%assign %%cylinder %%i / _CHS_HEADS
%if %%cylinder >= 1024
 %assign %%cylinder 1023
%endif
		istruc PARTINFO_CHS_TUPLE
at pictHead,		db %%head
at pictSectorLow6
at pictCylinderHigh2,	db (%%sector + 1) | ((%%cylinder >> (8 - 6)) & 0C0h)
at pictCylinderLow8,	db (%%cylinder & 0FFh)
		iend
	%endmacro

	struc PARTINFO
piBoot:		resb 1
piStartCHS:	resb 3		; PARTINFO_CHS_TUPLE
piType:		resb 1
piEndCHS:	resb 3		; PARTINFO_CHS_TUPLE
piStart:	resd 1
piLength:	resd 1
	endstruc

%define STARTSFOLLOWS start=0

%if _MBR
CYLINDERS equ (_MBR_GAP_SIZE_SECTORS + _SPI + _CHS_HEADS * _CHS_SECTORS - 1) \
	/ (_CHS_HEADS * _CHS_SECTORS)

	addsection mbr, STARTSFOLLOWS vstart=7C00h
 %define STARTSFOLLOWS follows=mbr

mbr_start:
	cli
	cld
	xor ax, ax
	mov es, ax
	mov ds, ax
	mov ss, ax
	mov sp, 7C00h
	sti
	mov si, mbr_message
@@:
	lodsb
	test al, al
	jz @F
	mov ah, 0Eh
	mov bh, [462h]
	mov bl, 7
	int 10h
	jmp @B

@@:
	xor ax, ax
	int 13h
	xor ax, ax
	int 16h
	int 19h

mbr_message:
	db "Unable to boot, MBR loader not written.",13,10
	db 13,10
	db "Press any key to reboot.",13,10
	db 0

	times (512 - 2 - 4 * 16) - ($ - $$) db 0

%assign TOTAL_MBR_SECTORS CYLINDERS * _CHS_HEADS * _CHS_SECTORS
mbr_partition_table:
	istruc PARTINFO
at piBoot,	db 80h			; active primary partition
at piStartCHS
		chs_tuple _MBR_GAP_SIZE_SECTORS
at piType,	db _MBR_PART_TYPE
at piEndCHS
		chs_tuple (TOTAL_MBR_SECTORS - 1)
at piStart,	dd _MBR_GAP_SIZE_SECTORS
at piLength,	dd TOTAL_MBR_SECTORS - _MBR_GAP_SIZE_SECTORS
	iend

	times (512 - 2) - ($ - $$) db 0
mbr_signature:
	dw 0AA55h
%endif