;------------------------------------------------------------------------------ ;* ;* Copyright 2006 - 2007, Intel Corporation ;* All rights reserved. This program and the accompanying materials ;* are licensed and made available under the terms and conditions of the BSD License ;* which accompanies this distribution. The full text of the license may be found at ;* http://opensource.org/licenses/bsd-license.php ;* ;* THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, ;* WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. ;* ;* bs16.asm ;* ;* Abstract: ;* ;------------------------------------------------------------------------------ .model small .stack .486p .code FAT_DIRECTORY_ENTRY_SIZE EQU 020h FAT_DIRECTORY_ENTRY_SHIFT EQU 5 BLOCK_SIZE EQU 0200h BLOCK_MASK EQU 01ffh BLOCK_SHIFT EQU 9 ; "EFILDR_____" LOADER_FILENAME_PART1 EQU 04c494645h ; "EFIL" LOADER_FILENAME_PART2 EQU 036315244h ; "DR16" LOADER_FILENAME_PART3 EQU 020202036h ; "6___" org 0h Ia32Jump: jmp BootSectorEntryPoint ; JMP inst - 3 bytes nop OemId db "INTEL " ; OemId - 8 bytes ; BPB data below will be fixed by tool SectorSize dw 0 ; Sector Size - 16 bits SectorsPerCluster db 0 ; Sector Per Cluster - 8 bits ReservedSectors dw 0 ; Reserved Sectors - 16 bits NoFats db 0 ; Number of FATs - 8 bits RootEntries dw 0 ; Root Entries - 16 bits Sectors dw 0 ; Number of Sectors - 16 bits Media db 0 ; Media - 8 bits - ignored SectorsPerFat dw 0 ; Sectors Per FAT - 16 bits SectorsPerTrack dw 0 ; Sectors Per Track - 16 bits - ignored Heads dw 0 ; Heads - 16 bits - ignored HiddenSectors dd 0 ; Hidden Sectors - 32 bits - ignored LargeSectors dd 0 ; Large Sectors - 32 bits PhysicalDrive db 0 ; PhysicalDriveNumber - 8 bits - ignored CurrentHead db 0 ; Current Head - 8 bits Signature db 0 ; Signature - 8 bits - ignored Id db " " ; Id - 4 bytes FatLabel db " " ; Label - 11 bytes SystemId db "FAT16 " ; SystemId - 8 bytes BootSectorEntryPoint: ASSUME ds:@code ASSUME ss:@code ; **************************************************************************** ; Start Print ; **************************************************************************** lea si, cs:[StartString] call PrintString ; **************************************************************************** ; Print over ; **************************************************************************** mov ax,cs ; ax = 0 mov ss,ax ; ss = 0 add ax,1000h mov ds,ax mov sp,07c00h ; sp = 0x7c00 mov bp,sp ; bp = 0x7c00 mov ah,8 ; ah = 8 - Get Drive Parameters Function mov byte ptr [bp+PhysicalDrive],dl ; BBS defines that BIOS would pass the booting driver number to the loader through DL int 13h ; Get Drive Parameters xor ax,ax ; ax = 0 mov al,dh ; al = dh inc al ; MaxHead = al + 1 push ax ; 0000:7bfe = MaxHead mov al,cl ; al = cl and al,03fh ; MaxSector = al & 0x3f push ax ; 0000:7bfc = MaxSector cmp word ptr [bp+SectorSignature],0aa55h ; Verify Boot Sector Signature jne BadBootSector mov cx,word ptr [bp+RootEntries] ; cx = RootEntries shl cx,FAT_DIRECTORY_ENTRY_SHIFT ; cx = cx * 32 = cx * sizeof(FAT_DIRECTORY_ENTRY) = Size of Root Directory in bytes mov bx,cx ; bx = size of the Root Directory in bytes and bx,BLOCK_MASK ; See if it is an even number of sectors long jne BadBootSector ; If is isn't, then the boot sector is bad. mov bx,cx ; bx = size of the Root Directory in bytes shr bx,BLOCK_SHIFT ; bx = size of Root Directory in sectors mov al,byte ptr [bp+NoFats] ; al = NoFats xor ah,ah ; ah = 0 ==> ax = NoFats mul word ptr [bp+SectorsPerFat] ; ax = NoFats * SectorsPerFat add ax,word ptr [bp+ReservedSectors] ; ax = NoFats * SectorsPerFat + ReservedSectors = RootLBA push ds pop es xor di,di ; Store directory in es:di = 1000:0000 call ReadBlocks ; Read entire Root Directory add ax,bx ; ax = NoFats * SectorsPerFat + ReservedSectors + RootDirSectors = FirstClusterLBA (FirstDataSector) mov word ptr [bp],ax ; Save FirstClusterLBA (FirstDataSector) for later use ; dx - variable storage (initial value is 0) ; bx - loader (initial value is 0) xor dx, dx xor bx, bx FindEFILDR: cmp dword ptr [di],LOADER_FILENAME_PART1 ; Compare to "EFIL" jne FindVARSTORE cmp dword ptr [di+4],LOADER_FILENAME_PART2 jne FindVARSTORE cmp dword ptr [di+7],LOADER_FILENAME_PART3 jne FindVARSTORE mov bx, word ptr [di+26] ; bx = Start Cluster for EFILDR <---------------------------------- test dx, dx je FindNext ; Efivar.bin is not loaded jmp FoundAll FindVARSTORE: ; if the file is not loader file, see if it's "EFIVAR BIN" cmp dword ptr [di], 056494645h ; Compare to "EFIV" jne FindNext cmp dword ptr [di+4], 020205241h ; Compare to "AR " jne FindNext cmp dword ptr [di+7], 04e494220h ; Compare to " BIN" jne FindNext mov dx, di ; dx = Offset of Start Cluster for Efivar.bin <--------------------- add dx, 26 test bx, bx je FindNext ; Efildr is not loaded jmp FoundAll FindNext: ; go to next find add di,FAT_DIRECTORY_ENTRY_SIZE ; Increment di sub cx,FAT_DIRECTORY_ENTRY_SIZE ; Decrement cx ; TODO: jump to FindVarStore if ... jne FindEFILDR jmp NotFoundAll FoundAll: FoundEFILDR: mov cx,bx ; cx = Start Cluster for EFILDR <---------------------------------- mov ax,cs ; Destination = 2000:0000 add ax,2000h mov es,ax xor di,di ReadFirstClusterOfEFILDR: mov ax,cx ; ax = StartCluster sub ax,2 ; ax = StartCluster - 2 xor bh,bh mov bl,byte ptr [bp+SectorsPerCluster] ; bx = SectorsPerCluster push dx mul bx pop dx ; ax = (StartCluster - 2) * SectorsPerCluster add ax, word ptr [bp] ; ax = FirstClusterLBA + (StartCluster-2)*SectorsPerCluster xor bh,bh mov bl,byte ptr [bp+SectorsPerCluster] ; bx = Number of Sectors in a cluster push es call ReadBlocks pop ax JumpIntoFirstSectorOfEFILDR: mov word ptr [bp+JumpSegment],ax JumpFarInstruction: db 0eah JumpOffset: dw 0000h JumpSegment: dw 2000h PrintString: mov ax,0b800h mov es,ax mov ax, 07c0h mov ds, ax mov cx, 7 mov di, 160 rep movsw ret ; **************************************************************************** ; ReadBlocks - Reads a set of blocks from a block device ; ; AX = Start LBA ; BX = Number of Blocks to Read ; ES:DI = Buffer to store sectors read from disk ; **************************************************************************** ; cx = Blocks ; bx = NumberOfBlocks ; si = StartLBA ReadBlocks: pusha add eax,dword ptr [bp+LBAOffsetForBootSector] ; Add LBAOffsetForBootSector to Start LBA add eax,dword ptr [bp+HiddenSectors] ; Add HiddenSectors to Start LBA mov esi,eax ; esi = Start LBA mov cx,bx ; cx = Number of blocks to read ReadCylinderLoop: mov bp,07bfch ; bp = 0x7bfc mov eax,esi ; eax = Start LBA xor edx,edx ; edx = 0 movzx ebx,word ptr [bp] ; bx = MaxSector div ebx ; ax = StartLBA / MaxSector inc dx ; dx = (StartLBA % MaxSector) + 1 sub bx,dx ; bx = MaxSector - Sector inc bx ; bx = MaxSector - Sector + 1 cmp cx,bx ; Compare (Blocks) to (MaxSector - Sector + 1) jg LimitTransfer mov bx,cx ; bx = Blocks LimitTransfer: push cx mov cl,dl ; cl = (StartLBA % MaxSector) + 1 = Sector xor dx,dx ; dx = 0 div word ptr [bp+2] ; ax = ax / (MaxHead + 1) = Cylinder ; dx = ax % (MaxHead + 1) = Head push bx ; Save number of blocks to transfer mov dh,dl ; dh = Head mov bp,07c00h ; bp = 0x7c00 mov dl,byte ptr [bp+PhysicalDrive] ; dl = Drive Number mov ch,al ; ch = Cylinder mov al,bl ; al = Blocks mov ah,2 ; ah = Function 2 mov bx,di ; es:bx = Buffer address int 013h jc DiskError pop bx pop cx movzx ebx,bx add esi,ebx ; StartLBA = StartLBA + NumberOfBlocks sub cx,bx ; Blocks = Blocks - NumberOfBlocks mov ax,es shl bx,(BLOCK_SHIFT-4) add ax,bx mov es,ax ; es:di = es:di + NumberOfBlocks*BLOCK_SIZE cmp cx,0 jne ReadCylinderLoop popa ret ; **************************************************************************** ; ERROR Condition: ; **************************************************************************** NotFoundAll: ; if we found EFILDR, continue test bx,bx jne FoundEFILDR BadBootSector: DiskError: lea si, cs:[ErrorString] call PrintString Halt: jmp Halt StartString: db 'B', 0ch, 'S', 0ch, 't', 0ch, 'a', 0ch, 'r', 0ch, 't', 0ch, '!', 0ch ErrorString: db 'B', 0ch, 'E', 0ch, 'r', 0ch, 'r', 0ch, 'o', 0ch, 'r', 0ch, '!', 0ch ; **************************************************************************** ; LBA Offset for BootSector, need patched by tool for HD boot. ; **************************************************************************** org 01fah LBAOffsetForBootSector: dd 0h ; **************************************************************************** ; Sector Signature ; **************************************************************************** org 01feh SectorSignature: dw 0aa55h ; Boot Sector Signature end