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Posted: **Sat May 14, 2011 9:14 pm**

So, I tried to write floppy driver (that's just initializing and read functions), but get #GP.
Bochs tells just: refetch: getHostMemAddr vetoed direct read, pAddr=0x000a0000
I tried to find out where is an error, but wasn't succeeded.
I read data to RAM address 0000.
IRQ6 handler just sets flag (floppy_int_active) and timer handler increments tick_count.
So, that's floppy driver code:

Code: Select all

;Registers
FLOP_SRB    equ    3F1h
FLOP_DOR    equ    3F2h
FLOP_TDR    equ    3F3h
FLOP_MSR    equ    3F4h
FLOP_DSR    equ    3F4h
FLOP_FIFO   equ    3F5h
FLOP_DIR    equ    3F7h
FLOP_CCR    equ    3F7h

FDD_read:
        call FDD_init
        mov bh,18
        call delay
        ;speed 500 kbyte/sec
        mov dx,FLOP_DIR;FLOP_DIR
        xor al,al
        out dx,al
        ;3 times try to recolibrate
        mov cl,3
 .recalibre_retry:
        call FDD_recalibrate
        jc .error
        call FDD_sense_interrupt;take down the order
        jnc .recalibre_success
        loop .recalibre_retry
        jmp .error

 .recalibre_success:
        call FDD_seek;go to first track
        jc .error
        call FDD_sense_interrupt
        jc .error
        mov bh,1
        call delay
        call DMA_init
        mov bh,1
        call delay
        mov cl,1
        call FDD_read_sector
        mov bh,1
        call FDD_stop
        ret


 .error:
        xor ecx,ecx
        mov esi,floppy_error
        int 1h
        ret


;DMA initialize
DMA_init:
        xor ebx,ebx;buffer address
        cli
        ;read
        mov al,46h
        out 12,al;reset trigger
        out 11,al;set mode
        mov al,bl
        out 4,al;address - 0000
        out 4,al;
        out 81h,al
        ;how many bytes to read
        mov ax,511;sector_size-1
        out 5,al
        mov al,ah
        out 5,al
        mov al,2;de-block channel 2 of controller
        out 10,al
        sti
        ret

;al - byte to send
FDD_init:
        mov dx,FLOP_DOR
        xor ax,ax
        out dx,al
        mov al,00011100b ; Motor0, Reset, DMA
        out dx,al
        ret

FDD_stop:
        mov al,00001100b ; DMA, Reset
        mov dx,FLOP_DOR
        out dx,al
        xor al,al
        out dx,al
        ret

FDD_send_byte:
        pusha
        clc
        mov dx,FLOP_MSR;reset controller
        mov cx,0FFFFh
        push ax
 .FDD_send_byte_loop:
        in al,dx
        and al,11000000b
        cmp al,10000000b;check MSR - is floppy free and ready?
        je .FDD_send_byte_ready
        loop .FDD_send_byte_loop
 .FDD_send_byte_ready:
        pop ax
        mov dx,FLOP_FIFO
        out dx,al
        popa
        ret
 .FDD_send_byte_err:
        xor ecx,ecx
        mov esi,floppy_error
        int 1h
        stc
        popa
        ret

;al - result
FDD_recv_byte:
        push cx
        clc
        mov dx, FLOP_MSR
        mov cx, 0FFFFh
 .FDD_recv_byte_loop:
        in al, dx
        and al, 11000000b
        cmp al, 11000000b;check MSR - is floppy free?
        jne .FDD_recv_byte_ready
        loop .FDD_recv_byte_loop
 .FDD_recv_byte_ready:
        mov dx, FLOP_FIFO
        in al, dx
 .FDD_recv_byte_exit:
        pop cx
        ret
 .FDD_recv_byte_err:
        xor ecx,ecx
        mov esi,floppy_error
        int 1h
        stc
        pop cx
        ret

FDD_sense_interrupt:
        ;command code
        mov al,00001000b
        call FDD_send_byte
        jc .FDD_sense_int_status_exit;we make suggestions basing on carry flag
        ;read st0
         call FDD_recv_byte
        jc .FDD_sense_int_status_exit
        and al,11110000b
        cmp al,00100000b
        jne .FDD_sense_int_status_error
        call FDD_recv_byte
        jc .FDD_sense_int_status_exit
        test al,al
        jnz .FDD_sense_int_status_error
 .FDD_sense_int_status_exit:
        ret
 .FDD_sense_int_status_error:
        xor ecx,ecx
        mov esi,floppy_error
        int 1h
        stc
        ret

FDD_motor_stop:
        mov dx,FLOP_DOR
        mov al,00001100b;Motor0, Reset
        out dx,al
        xor al,al
        out dx,al
        ret

FDD_recalibrate:
        mov al,00000111b
        call FDD_send_byte
        jc .FDD_recalibrate_exit
        xor al,al
        call FDD_send_byte
        jc .FDD_recalibrate_exit
        call FDD_wait_end
 .FDD_recalibrate_exit:
        ret

FDD_seek:
        mov al,00001111b
        call FDD_send_byte
        jc .FDD_seek_exit
        xor al,al
        call FDD_send_byte
        jc .FDD_seek_exit
        call FDD_send_byte
        jc .FDD_seek_exit
        call FDD_wait_end
 .FDD_seek_exit:
        ret

FDD_wait_end:
 .FDD_wait_end_loop:
        cmp [floppy_int_active],1
        jne .FDD_wait_end_loop
 .FDD_wait_end_exit:
        mov [floppy_int_active],0
        ret

FDD_read_sector:
        ;CL - sector number
        pushad
        ;part 1
        mov al,1100110b
        call FDD_send_byte
        jc .FDD_read_sector_exit
        ;part 2
        xor al,al
        call FDD_send_byte
        jc .FDD_read_sector_exit
        ;cylinder
        call FDD_send_byte
        jc .FDD_read_sector_exit
        ;head
        call FDD_send_byte
        jc .FDD_read_sector_exit
        ;sector #
        mov al,cl
        call FDD_send_byte
        jc .FDD_read_sector_exit
        mov al,2;sector size is 512
        call FDD_send_byte
        jc .FDD_read_sector_exit
        mov al,19
        call FDD_send_byte
        jc .FDD_read_sector_exit
        mov al,1Bh;GPL
        call FDD_send_byte
        jc .FDD_read_sector_exit
        mov al,0FFh
        call FDD_send_byte
        jc .FDD_read_sector_exit

        call FDD_wait_end
        ;ST0
        call FDD_recv_byte
        jc .FDD_read_sector_exit
        test al,11111100b
        jnz .FDD_read_sector_exit
        ;ST1 and ST2
        xor cx,cx
        mov cl,2
 .FDD_read_sector_STX:
        call FDD_recv_byte
        jc .FDD_read_sector_exit
        test al,al
        jnz .FDD_read_sector_error
        loop .FDD_read_sector_STX
        ;Read C H R N
        mov cl,4
 .FDD_read_sector_result:
        call FDD_recv_byte
        loop .FDD_read_sector_result
 .FDD_read_sector_exit:
        popad
        ret
 .FDD_read_sector_error:
        xor ecx,ecx
        mov esi,floppy_error
        int 1h
        stc
        popad
        ret


;bh - 1/18.8 of sec
delay:
        mov [tick_count],0;tick_count is incremented by timer handler
 .loop:
        cmp [tick_count],bh
        jl .loop
        ret


;;;;;;;;;;;;;;;;;;;;;;;;;Vars;;;;;;;;;;;;;;;;;

floppy_int_active  db     0
tick_count         db     0

Posted: **Sun May 15, 2011 12:10 am**

I've found problem in stack using, but now I've got funny results:
1)In Virtual Box:
Driver works perfectly if paging isn't enabled. I operate with another page (the first one - cause write to start of RAM) and it crashes.
2)In Bochs:
Everything just perfect?!

I really don't know why 2 different VM behave themselves so strange...
Can anybody suggest why it's like that?

Posted: **Mon May 16, 2011 4:19 am**

I really don't know why two different VM behave themselves so strange

No two computers are the same, neither are VMs. VMs are especially known for emulating stuff to the extent needed for things to just work. If your code is broken, chances are at least VM will choke on it. Apparently bochs makes the right guess about what you want while VirtualBox notices your code is actually nuts and refuses.

Posted: **Mon May 16, 2011 11:21 pm**

So, I'll trust Bochs.

Posted: **Tue May 17, 2011 1:18 am**

I wouldn't do that if I were you. The fact that bochs doesn't choke on something won't mean it ain't broken. The fact that virtual box doesn't like your code is an indicator that you're doing something wrong, and by ignoring that it might come back to bite you later on.

Posted: **Tue May 17, 2011 1:53 pm**

Of course I'm worried about that bug, but I can't find it. Virtual Box has no debugger (it doesn't show fault details that make my exception handlers - characteristic feature of it), so I use Bochs.

Posted: **Tue May 17, 2011 3:32 pm**

You don't need a debugger to debug. Do you know printf?

Posted: **Wed May 18, 2011 12:05 am**

printf? What's printf?

Of course I know, but VirtualBox's screen is clear, however 'hello' is printed when enter to PM. My handlers print information about exception, but it isn't displayed on the screen, but when I turn off VirtualBox screen blinks and show this information. VMWare has't this problem.

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