Add VBR stub

This commit is contained in:
2025-10-05 17:24:25 +02:00
parent 4e7baf302c
commit 64733914f2
2 changed files with 114 additions and 0 deletions

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@@ -3,3 +3,4 @@ PROJECT(BOOTSECT)
# Compile boot sectors
compile_bootsector(mbrboot ${BOOTSECT_SOURCE_DIR}/mbrboot.S 0x7C00 Start)
compile_bootsector(espboot ${BOOTSECT_SOURCE_DIR}/espboot.S 0x7C00 Start)

113
boot/bootsect/espboot.S Normal file
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@@ -0,0 +1,113 @@
/**
* PROJECT: ExectOS
* COPYRIGHT: See COPYING.md in the top level directory
* FILE: boot/bootsect/espboot.S
* DESCRIPTION: XT Boot Loader ESP boot code (FAT32)
* DEVELOPERS: Aiken Harris <harraiken91@gmail.com>
*/
.text
.code16
.global Start
Start:
/* Jump to the real start to omit the BPB (BIOS Parameter Block) */
jmp RealStart
nop
/* BIOS Parameter Block */
OsName:
.ascii "XTOS "
OsVersion:
.ascii "1.0"
BytesPerSector:
.word 512
SectorsPerCluster:
.byte 2
ReservedSectors:
.word 8
FatCopies:
.byte 1
RootDirEntries:
.word 1024
TotalSectors:
.word 0
MediaType:
.byte 0xF8
SectorsPerFat:
.word 0
SectorsPerTrack:
.word 17
NumberOfHeads:
.word 0
HiddenSectors:
.long 0
TotalBigSectors:
.long 0x200000
BigSectorsPerFat:
.long 0x1FE0
ExtendedFlags:
.word 0
FsVersion:
.word 0
RootDirStartCluster:
.long 0
FSInfoSector:
.word 0
BackupBootSector:
.word 6
Reserved:
.fill 12, 1, 0
DriveNumber:
.byte 0x80
CurrentHead:
.byte 0
Signature:
.byte 0x29
SerialNumber:
.long 0
VolumeLabel:
.ascii "NO NAME "
FileSystem:
.ascii "FAT32 "
RealStart:
/* Set segments and stack */
cli
cld
xorw %ax, %ax
movw %ax, %ds
movw %ax, %es
movw %ax, %ss
movw $0x7C00, %bp
leaw -16(%bp), %sp
sti
/* Print message */
movw $msgUnavailable, %si
call Print
/* Wait for key press and reboot */
xorw %ax, %ax
int $0x16
int $0x19
Print:
/* Simple routine to print messages */
lodsb
orb %al, %al
jz DonePrint
movb $0x0E, %ah
movw $0x07, %bx
int $0x10
jmp Print
DonePrint:
retw
msgUnavailable:
.ascii "XTLDR requires EFI-based system!\r\nPress any key to restart\r\n"
/* Fill the rest of the VBR with zeros and add VBR signature at the end */
.fill (510 - (. - Start)), 1, 0
.word 0xAA55