RealModeOS/ata.asm at main · Xeraster/RealModeOS · GitHub

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;=============================================================================
; ATA read sectors (LBA mode)
;
; @param EAX Logical Block Address of sector
; @param CL  Number of sectors to read. not working in real mode and isn't easy to fix
; @param RDI The address of buffer to put data obtained from disk
;
; @return None
;=============================================================================
;whatever. good enough
ata_lba_read:
            ;;it's broken in real mode. you can only read 1 sector per command in real mode and by the looks of things, it would be way harder to fix than it's worthwhile
            mov cl, 1
               pushad
               and eax, 0x0FFFFFFF
               push eax
               push ebx
               push ecx
               push edx
               push edi

               mov ebx, eax         ; Save LBA in RBX

               mov edx, 0x01F6      ; Port to send drive and bit 24 - 27 of LBA
               shr eax, 24          ; Get bit 24 - 27 in al
               or al, 11100000b     ; Set bit 6 in al for LBA mode
               out dx, al

               mov edx, 0x01F2      ; Port to send number of sectors
               mov al, cl           ; Get number of sectors from CL
               out dx, al

               mov edx, 0x1F3       ; Port to send bit 0 - 7 of LBA
               mov eax, ebx         ; Get LBA from EBX
               out dx, al

               mov edx, 0x1F4       ; Port to send bit 8 - 15 of LBA
               mov eax, ebx         ; Get LBA from EBX
               shr eax, 8           ; Get bit 8 - 15 in AL
               out dx, al


               mov edx, 0x1F5       ; Port to send bit 16 - 23 of LBA
               mov eax, ebx         ; Get LBA from EBX
               shr eax, 16          ; Get bit 16 - 23 in AL
               out dx, al

               mov edx, 0x1F7       ; Command port
               mov al, 0x20         ; Read with retry.
               out dx, al

.still_going:  in al, dx
               test al, 8           ; the sector buffer requires servicing.
               jz .still_going      ; until the sector buffer is ready.

               mov eax, 256         ; to read 256 words = 1 sector
               xor bx, bx
               mov bl, cl           ; read CL sectors
               mul bx
               mov ecx, eax         ; RCX is counter for INSW
               mov edx, 0x1F0       ; Data port, in and out

                ;;whatever arcane bullshit this is doesn't work, at least not in real mode
               ;rep insw             ; in to [RDI]
               ;mov ecx, 256
            ataFuck:
            push ax
            ;rep ins ax, dx;;doesn't work. we have to do this the dumb but reliable way i guess
                in ax, dx
                mov [es:di], ax
                inc di
                inc di
                dec ecx
            pop ax
            cmp cx, 0
            jne ataFuck

               pop edi
               pop edx
               pop ecx
               pop ebx
               pop eax
               popad
            ret


;=============================================================================
; ATA write sectors (LBA mode)
;
; @param EAX Logical Block Address of sector
; @param CL  Number of sectors to write
; @param RDI The address of data to write to the disk
;
; @return None
;=============================================================================
 ;;not tested, probably doesn't work just because the ata read command didn't work without extensive modification
ata_lba_write:
    pushad
    and eax, 0x0FFFFFFF
    push eax
    push ebx
    push ecx
    push edx
    push edi

    mov ebx, eax         ; Save LBA in RBX

    mov edx, 0x01F6      ; Port to send drive and bit 24 - 27 of LBA
    shr eax, 24          ; Get bit 24 - 27 in al
    or al, 11100000b     ; Set bit 6 in al for LBA mode
    out dx, al

    mov edx, 0x01F2      ; Port to send number of sectors
    mov al, cl           ; Get number of sectors from CL
    out dx, al

    mov edx, 0x1F3       ; Port to send bit 0 - 7 of LBA
    mov eax, ebx         ; Get LBA from EBX
    out dx, al

    mov edx, 0x1F4       ; Port to send bit 8 - 15 of LBA
    mov eax, ebx         ; Get LBA from EBX
    shr eax, 8           ; Get bit 8 - 15 in AL
    out dx, al


    mov edx, 0x1F5       ; Port to send bit 16 - 23 of LBA
    mov eax, ebx         ; Get LBA from EBX
    shr eax, 16          ; Get bit 16 - 23 in AL
    out dx, al

    mov edx, 0x1F7       ; Command port
    mov al, 0x30         ; Write with retry.
    out dx, al

.still_going:  in al, dx
    test al, 8           ; the sector buffer requires servicing.
    jz .still_going      ; until the sector buffer is ready.

    mov eax, 256         ; to read 256 words = 1 sector
    xor bx, bx
    mov bl, cl           ; write CL sectors
    mul bx
    mov ecx, eax         ; RCX is counter for OUTSW
    mov edx, 0x1F0       ; Data port, in and out
    mov esi, edi
    rep outsw            ; out

    pop edi
    pop edx
    pop ecx
    pop ebx
    pop eax
    popad
ret