Using BIOS INT 13h, ah=42h to read from USB
I am using BIOS and want to make a self made operation system.
I am using the LBA method (int 0x13, ah=0x42) and successfully made it work on QEMU. But, when I let it work on a real PC, it does not work. It can only read 512bytes from USB.
When I used int 0x10 to show the problem, I finally figured out the problem.
The memory does not move to referenced memory at all.
My code is written below.
[bits 16]
[ORG 0x7c00]
;; BPB Structure
JMP entry ;BS_jmpBoot
NOP
BS_OEMName DB "HARIBOTE"
BPB_BytsPerSec DW 0x0200
BPB_SecPerClus DB 0x01
BPB_RsvdSecCnt DW 0x0001
BPB_NumFATs DB 0x02
BPB_RootEntCnt DW 0x0000
BPB_TotSec16 DW 0x0000
BPB_Media DB 0xf8
BPB_FATSz16 DW 0x0000
BPB_SecPerTrk DW 0xffff
BPB_NumHeads DW 0x0001
BPB_HiDDSec DD 0x00000000
BPB_TotSec32 DD 0x00ee5000
BPB_FATSz32 DD 0x000000ed
BPB_ExtFlags DW 0x0000
BPB_FSVer DW 0x0000
BPB_RootClus DD 0x00000000
BPB_FSInfo DW 0x0001
BPB_BkBootSec DW 0x0000
times 12 DB 0 ;BPB_Reserverd
BS_DrvNum DB 0x80
BS_Reserved1 DB 0x00
BS_BootSig DB 0x29
BS_VolID DD 0xa0a615c
BS_VolLab DB "ISHIHA BOOT"
BS_FileSysType DB "FAT32 "
entry:
CLI
MOV AX, 0
MOV DS, AX
MOV ES, AX
MOV BX, AX
MOV CX, AX
MOV SP, 0x7c00
prepare:
PUSH CS
POP DS
PUSH CS
POP ES
STI
mov ah, 0x41 ; Set Function 0x41
mov word bx, 0x55AA
push dx ; Save old Drive Identifier
mov dl, 0x80 ; Load 'Active' ID Into dl, commented out to keep bios setting of dl (should be active drive)
int 0x13 ; Call Interupt
jc unsupported ; If Extentions aren't Supported, Jump
xor ax, ax
add ax, 1 ; clear carry flag
XOR EDI, EDI
MOV AH, 0x45
MOV AL, 0x01
MOV DL, 0x80
INT 0x13
loop:
MOV CL, 0
retry:
PUSH DS
PUSHAD
MOV DL, 0x80
MOV AH, 0x42
MOV AL, 0x00
MOV SI, DAPS
INT 0x13
JNC next
ADD CL, 1
MOV DL, 0x80
MOV AH, 0x00
INT 0x13
CMP CL, 6
JAE error
JMP retry
next:
XOR EAX, EAX
XOR EBX, EBX
XOR ECX, ECX
ADD EDI, 1
MOV ECX, lba0
MOV [ECX], EDI
XOR EAX, EAX
XOR ECX, ECX
XOR EBP, EBP
MOV AX, [addr]
MOV ECX, addr
MOV EBX, segm
ADD AX, 0x200
ADC BP, 0
SHL BP, 12
ADD BP, [segm]
MOV [EBX], BP
MOV [ECX], AX
MOV [EBX], BP
CMP EDI, 0x16a
JB loop
MOV ECX, 0xc200
JMP check
interrupt:
MOV EAX, 0x0000
MOV EBX, EAX
MOV EDX, EAX
MOV EBP, EAX
MOV ESI, EAX
MOV EDI, EAX
MOV CH, 10
MOV [0x0ff0], CH
MOV ECX, EAX
JMP 0xc200
error:
POPAD
POP DS
MOV SI,msg
putloop:
MOV AL,[SI]
ADD SI,1
CMP AL,0
JE fin
MOV AH,0x0e
MOV BX,15
INT 0x10
JMP putloop
fin:
HLT
JMP fin
msg:
DB 0x0a, 0x0a
DB "load error"
DB 0x0a
DB 0
msg1:
DB 0x0a, 0x0a
DB "not supported"
DB 0x0a
DB 0
unsupported:
MOV SI, msg1
JMP putloop
drv: DB 0x80
DAPS: DB 0x10 ; Size of Structure (16 bytes, always this for DAPS)
DB 0 ; Always 0
DB 1 ; Number of Sectors to Read (1x512)
DB 0 ; Always 0
addr: DW 0x8000 ; Target Location for Reading To (0x8000 = 0x0800:0x0000)
segm: DW 0x0000 ; Page Table (0, Disabled)
lba0: DD 1 ; Read from 2nd block (code I want to load)
DD 0 ; Large LBAs, dunno what this does
check:
MOV AH, 0x0e
MOV AL, [ECX]
ADD AL, 48
MOV BX, 0
INT 0x10
ADD ECX, 1
CMP ECX, 0xc400
JNE check
JMP interrupt
RESB 0x01fe-($-$$)
DW 0AA55h
So my question is:
Is BIOS access memory restricted during certain periods?
My BIOS is SMBIOS 3.0.0 and the model is ASUS x540la.
Michael Petch1 Answer
[bits 16]
[ORG 0x7c00]
;; BPB Structure
JMP entry ;BS_jmpBoot
NOP
BS_OEMName DB "HARIBOTE"
BPB_BytsPerSec DW 0x0200
BPB_SecPerClus DB 0x01
BPB_RsvdSecCnt DW 0x0001
BPB_NumFATs DB 0x02
BPB_RootEntCnt DW 0x0000
BPB_TotSec16 DW 0x0000
BPB_Media DB 0xf8
BPB_FATSz16 DW 0x0000
BPB_SecPerTrk DW 0xffff
BPB_NumHeads DW 0x0001
BPB_HiDDSec DD 0x00000000
BPB_TotSec32 DD 0x00ee5000
BPB_FATSz32 DD 0x000000ed
BPB_ExtFlags DW 0x0000
BPB_FSVer DW 0x0000
BPB_RootClus DD 0x00000000
BPB_FSInfo DW 0x0001
BPB_BkBootSec DW 0x0000
times 12 DB 0 ;BPB_Reserverd
BS_DrvNum DB 0x80
BS_Reserved1 DB 0x00
BS_BootSig DB 0x29
BS_VolID DD 0xa0a615c
BS_VolLab DB "ISHIHA BOOT"
BS_FileSysType DB "FAT32 "
entry:
CLI
MOV AX, 0
MOV DS, AX
MOV SS, AX
MOV ES, AX
MOV BX, AX
MOV CX, AX
MOV SP, 0x7c00
prepare:
STI
MOV [drv], DL
CMP DL, 0x80
JB unsupported ; HDD系デバイスでなければエラー
MOV AH, 0x0e
MOV AL, [drv]
MOV BX, 0
INT 0x10
mov ah, 0x41 ; Set Function 0x41
mov word bx, 0x55aa
int 0x13 ; Call Interupt
jc unsupported ; If Extentions aren't Supported, Jump
xor ax, ax
add ax, 1 ; clear carry flag
XOR EDI, EDI
MOV AH, 0x45
MOV AL, 0x01
MOV DL, 0x80
INT 0x13
MOV AX, 0
MOV DS, AX
loop:
MOV CL, 0
retry:
PUSH DS
PUSHAD
MOV DL, [drv]
MOV AH, 0x42
MOV AL, 0x00
MOV SI, DAPS
INT 0x13
JNC next
ADD CL, 1
MOV DL, 0x80
MOV AH, 0x00
INT 0x13
CMP CL, 6
JAE error
JMP retry
next:
XOR EAX, EAX
XOR EBX, EBX
XOR ECX, ECX
ADD EDI, 1
MOV ECX, lba0
MOV [ECX], EDI
XOR EAX, EAX
XOR ECX, ECX
XOR EBP, EBP
MOV AX, [addr]
MOV ECX, addr
MOV EBX, segm
ADD AX, 0x200
ADC BP, 0
SHL BP, 12
ADD BP, [segm]
MOV [EBX], BP
MOV [ECX], AX
MOV [EBX], BP
CMP EDI, 0x16a
JB loop
MOV ECX, 0xc200
JMP check
interrupt:
MOV EAX, 0x0000
MOV EBX, EAX
MOV EDX, EAX
MOV EBP, EAX
MOV ESI, EAX
MOV EDI, EAX
MOV CH, 10
MOV [0x0ff0], CH
MOV ECX, EAX
JMP 0x0000:0xc200
error:
POPAD
POP DS
MOV SI,msg
putloop:
MOV AL,[SI]
ADD SI,1
CMP AL,0
JE fin
MOV AH,0x0e
MOV BX,0
INT 0x10
JMP putloop
fin:
HLT
JMP fin
msg:
DB 0x0a, 0x0a
DB "load error"
DB 0x0a
DB 0
msg1:
DB 0x0a, 0x0a
DB "not supported"
DB 0x0a
DB 0
unsupported:
MOV SI, msg1
JMP putloop
drv: DB 0x80
DAPS: DB 0x10 ; Size of Structure (16 bytes, always this for DAPS)
DB 0 ; Always 0
DB 1 ; Number of Sectors to Read (1x512)
DB 0 ; Always 0
addr: DW 0x8000 ; Target Location for Reading To (0x8000 = 0x0800:0x0000)
segm: DW 0x0000 ; Page Table (0, Disabled)
lba0: DD 1 ; Read from 2nd block (code I want to load)
DD 0 ; Large LBAs, dunno what this does
check:
MOV AH, 0x0e
MOV AL, [ECX]
ADD AL, 48
MOV BX, 0
INT 0x10
ADD ECX, 1
CMP ECX, 0xc400
JNE check
JMP interrupt
RESB 0x01fe-($-$$)
DW 0AA55h
Thank you, I finally figure out why.When I execute code above, it returned "not supported".It seems my bios does not support pure usb-hdd boot and my bios is usb-fdd emulator.All the question has been solved, thank you.
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