Add VBR stub

boot/bootsect/CMakeLists.txt

@@ -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)

boot/bootsect/espboot.S

@@ -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