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Optimized FAT32 bootsector to read more than 1 sector at a time on systems supporting LBA calls.

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svn path=/trunk/; revision=3045
This commit is contained in:
Brian Palmer 2002-06-11 05:41:45 +00:00
parent 6ac81e7954
commit 8bab1a8f2d
1 changed files with 43 additions and 23 deletions
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66
freeldr/bootsect/fat32.asm
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@ -116,34 +116,44 @@ LoadExtraBootCode:
; EAX has logical sector number to read
; CX has number of sectors to read
ReadSectors:
cmp eax,DWORD [BiosCHSDriveSize] ; Check if they are reading a sector within CHS range
jb ReadSectorsCHS ; Yes - go to the old CHS routine
cmp eax,DWORD [BiosCHSDriveSize] ; Check if they are reading a sector outside CHS range
jae ReadSectorsLBA ; Yes - go to the LBA routine
; If at all possible we want to use LBA routines because
; They are optimized to read more than 1 sector per read
ReadSectorsLBA:
pushad ; Save logical sector number & sector count
o32 push byte 0
push eax ; Put 64-bit logical block address on stack
push es ; Put transfer segment on stack
push bx ; Put transfer offset on stack
push byte 1 ; Set transfer count to 1 sector
push byte 0x10 ; Set size of packet to 10h
mov si,sp ; Setup disk address packet on stack
CheckInt13hExtensions: ; Now make sure this computer supports extended reads
CheckInt13hExtensions: ; Now check if this computer supports extended reads
mov ah,0x41 ; AH = 41h
mov bx,0x55aa ; BX = 55AAh
mov dl,[BYTE bp+BootDrive] ; DL = drive (80h-FFh)
int 13h ; IBM/MS INT 13 Extensions - INSTALLATION CHECK
jc PrintDiskError ; CF set on error (extensions not supported)
jc ReadSectorsCHS ; CF set on error (extensions not supported)
cmp bx,0xaa55 ; BX = AA55h if installed
jne PrintDiskError
jne ReadSectorsCHS
test cl,1 ; CX = API subset support bitmap
jz PrintDiskError ; Bit 0, extended disk access functions (AH=42h-44h,47h,48h) supported
jz ReadSectorsCHS ; Bit 0, extended disk access functions (AH=42h-44h,47h,48h) supported
popad ; Restore sector count & logical sector number
ReadSectorsLBA:
pushad ; Save logical sector number & sector count
cmp cx,64 ; Since the LBA calls only support 0x7F sectors at a time we will limit ourselves to 64
jbe ReadSectorsSetupDiskAddressPacket ; If we are reading less than 65 sectors then just do the read
mov cx,64 ; Otherwise read only 64 sectors on this loop iteration
ReadSectorsSetupDiskAddressPacket:
mov [LBASectorsRead],cx
o32 push byte 0
push eax ; Put 64-bit logical block address on stack
push es ; Put transfer segment on stack
push bx ; Put transfer offset on stack
push cx ; Set transfer count
push byte 0x10 ; Set size of packet to 10h
mov si,sp ; Setup disk address packet on stack
; Good, we're here so the computer supports LBA disk access
; So finish the extended read
mov dl,[BYTE bp+BootDrive] ; Drive number
mov ah,42h ; Int 13h, AH = 42h - Extended Read
int 13h ; Call BIOS
@ -153,20 +163,30 @@ CheckInt13hExtensions: ; Now make sure this computer supports extended rea
popad ; Restore sector count & logical sector number
inc eax ; Increment sector to read
movzx ebx,WORD [LBASectorsRead]
add eax,ebx ; Increment sector to read
shr ebx,4
mov dx,es
add dx,byte 20h ; Increment read buffer for next sector
add dx,bx ; Setup read buffer for next sector
mov es,dx
loop ReadSectorsLBA ; Read next sector
xor bx,bx
ret
sub cx,[LBASectorsRead]
jnz ReadSectorsLBA ; Read next sector
ret
LBASectorsRead:
dw 0
; Reads logical sectors into [ES:BX]
; EAX has logical sector number to read
; CX has number of sectors to read
ReadSectorsCHS:
popad ; Get logical sector number & sector count off stack
ReadSectorsCHSLoop:
pushad
xor edx,edx
movzx ecx,WORD [BYTE bp+SectorsPerTrack]
@ -198,7 +218,7 @@ ReadSectorsCHS:
add dx,byte 20h ; Increment read buffer for next sector
mov es,dx
loop ReadSectorsCHS ; Read next sector
loop ReadSectorsCHSLoop ; Read next sector
ret