Loading USB SecondStage Loader Problem

[Muneer]

Hi,


I know this has been discussed before and I have searched through almost all the topics related to this but the problem is that i still cant get it to work.
My Pc supports USB booting ( I can load my MBR and get it to work).
But When I load the second sector and jump to it , it triple faults in real hardware ( and not in virtual box or virtual pc or Bochs).
Also my Pc boots Usb as HDD

Code: Select all

               
Load_Second_Sector:

			Mov	Ax , 0x1000		; 	Segment Address To Copy Sector
			Mov	Es , Ax	
			Xor	Bx , Bx		;	Offset Address To Copy Sector

			Mov	Ah , 2			;	Copy Sector Function
			Mov	Al , 1		         	;	Number Of Sectors to Copy
			Mov	Ch , 0			;	Track Number
			Mov	Cl , 2			        ; 	Sector Number 
			Mov	Dh , 0			;	Head Number
			mov	Dl , [BootDiskNumber]   ; Drive Number With Which Bios Was Booted
			Int 	0x13
			Ret

BootDiskNumber: db 0

Thanks In Advance

[Combuster]

What's with the lack of error checking?

[Muneer]

This is supposed to be a basic bios call procedure . So I thought I could do without it. Does it make any difference?......

[Combuster]

Yes. It's called basic debugging skills.
How else do you think you can find out if the bios call is the problem? It even gives a description of the error if it has one.

(and on real hardware, you can have random read errors although for USB they should be rather unlikely)

[Muneer]

Thanks . I will check and post the result

[Muneer]

I still cant get it to work. No Error after reading the drive.
Here is the code with Extended Functions (unlike earlier with 02 funtion)

Code: Select all

DriveRead:

Mov	Ax , 0
Mov	Ds , Ax
Mov	Si , Packet

Mov	Ah , 0x42         ;  Extended Bios Drive Read Function
Mov	Dl , [BootDiskNumber] 	; Drive Number With Which Bios Was Booted
Int	0x13
Jnc	Continue
             Call Display_Error      ;   Procedure that prints "There is Error" to screen
Continue:


			
Packet:

db 16	;	Size Of packet
db  0	;	Should Be 0
db  1 ;	Number Of Sectors To Be  Read
db  0	;	Should Be 0
dw 0	;	Offset (1000:0000)
dw 1000	;	Segment
dd  1 , 0	;	Start Of Sector To Be Read (First sector of drive has number 0)


BootDiskNumber: db 0

Can Someone post code to read the second sector from a Usb-HDD . ....

[gerryg400]

Code: Select all

dw 1000   ;   Segment

Is that supposed to be 0x1000 ?

[Combuster]

Code: Select all

Jnc	Continue
             Call Display_Error      ;   Procedure that prints "There is Error" to screen
Continue: ; continue anyway

Doesn't this qualify as "print a message then crash anyway" (especially, crash before you can see the printout)

[Muneer]

Hi gerryg400,

Well you are right. That was supposed to be 0x1000. But anyways i had detected it just after posting that and the result is still the same.

Hi Combuster ,

It has a Cli and Hlt just after the code so that I can check whether the crash will print to the screen. But then It does not, So I have to take it as no error. Both the codes ( supposed to function similarly does not work out and both gives back "no error" result)

First Method:

Code: Select all

Load_Second_Sector:

         Mov   Ax , 0x1000      ;    Segment Address To Copy Sector
         Mov   Es , Ax   
         Xor   Bx , Bx      ;   Offset Address To Copy Sector

         Mov   Ah , 2         ;   Copy Sector Function
         Mov   Al , 1                  ;   Number Of Sectors to Copy
         Mov   Ch , 0         ;   Track Number
         Mov   Cl , 2                 ;    Sector Number
         Mov   Dh , 0         ;   Head Number
         mov   Dl , [BootDiskNumber]   ; Drive Number With Which Bios Was Booted
         Int    0x13
         Ret

BootDiskNumber: db 0

Second Method:

Code: Select all

DriveRead:

Mov   Ax , 0
Mov   Ds , Ax
Mov   Si , Packet

Mov   Ah , 0x42         ;  Extended Bios Drive Read Function
Mov   Dl , [BootDiskNumber]    ; Drive Number With Which Bios Was Booted
Int   0x13
Jnc   Continue
             Call Display_Error      ;   Procedure that prints "There is Error" to screen
Continue:


         
Packet:

db 16   ;   Size Of packet
db  0   ;   Should Be 0
db  1 ;   Number Of Sectors To Be  Read
db  0   ;   Should Be 0
dw 0   ;   Offset (1000:0000)
dw 0x1000   ;   Segment
dd  1 , 0   ;   Start Of Sector To Be Read (First sector of drive has number 0)


BootDiskNumber: db 0

VirtualBox when booting with Usb works all right with the first method ( I suppose it is because It emulates Usb FDD ), whereas with the second method it displays "There is Error" message as expected with my code ( May be because it doesn't emulate Usb HDD ). But in the real hardware neither causes a error ( My Pc supports only Usb HDD ) but looks as if the area to which the load was made doesn't have the value as expected.
I really cant understand what is going on.. Thabks