source: branches/minix3-book/drivers/tty/vidcopy.s@ 4

# 
! This file contains two specialized assembly code routines to update the 
! video memory. The routines can copy from user to video memory, or from
! video to video memory.   

! sections

.sect .text; .sect .rom; .sect .data; .sect .bss

! exported functions

.define _mem_vid_copy   ! copy data to video ram
.define _vid_vid_copy   ! move data in video ram

! The routines only guarantee to preserve the registers the C compiler
! expects to be preserved (ebx, esi, edi, ebp, esp, segment registers, and
! direction bit in the flags).

.sect .text
!*===========================================================================*
!*                              mem_vid_copy                                 *
!*===========================================================================*
! PUBLIC void mem_vid_copy(u16 *src, unsigned dst, unsigned count);
!
! Copy count characters from kernel memory to video memory.  Src is an ordinary
! pointer to a word, but dst and count are character (word) based video offset
! and count.  If src is null then screen memory is blanked by filling it with
! blank_color.

_mem_vid_copy:
        push    ebp
        mov     ebp, esp
        push    esi
        push    edi
        push    es
        mov     esi, 8(ebp)             ! source
        mov     edi, 12(ebp)            ! destination
        mov     edx, 16(ebp)            ! count
        mov     es, (_vid_seg)          ! segment containing video memory
        cld                             ! make sure direction is up
mvc_loop:
        and     edi, (_vid_mask)        ! wrap address
        mov     ecx, edx                ! one chunk to copy
        mov     eax, (_vid_size)
        sub     eax, edi
        cmp     ecx, eax
        jbe     0f
        mov     ecx, eax                ! ecx = min(ecx, vid_size - edi)
0:      sub     edx, ecx                ! count -= ecx
        shl     edi, 1                  ! byte address
        add     edi, (_vid_off)         ! in video memory
        test    esi, esi                ! source == 0 means blank the screen
        jz      mvc_blank
mvc_copy:
        rep                             ! copy words to video memory
    o16 movs
        jmp     mvc_test
mvc_blank:
        mov     eax, (_blank_color)     ! ax = blanking character
        rep
    o16 stos                            ! copy blanks to video memory
        !jmp    mvc_test
mvc_test:
        sub     edi, (_vid_off)
        shr     edi, 1                  ! back to a word address
        test    edx, edx
        jnz     mvc_loop
mvc_done:
        pop     es
        pop     edi
        pop     esi
        pop     ebp
        ret


!*===========================================================================*
!*                              vid_vid_copy                                 *
!*===========================================================================*
! PUBLIC void vid_vid_copy(unsigned src, unsigned dst, unsigned count);
!
! Copy count characters from video memory to video memory.  Handle overlap.
! Used for scrolling, line or character insertion and deletion.  Src, dst
! and count are character (word) based video offsets and count.

_vid_vid_copy:
        push    ebp
        mov     ebp, esp
        push    esi
        push    edi
        push    es
        mov     esi, 8(ebp)             ! source
        mov     edi, 12(ebp)            ! destination
        mov     edx, 16(ebp)            ! count
        mov     es, (_vid_seg)          ! segment containing video memory
        cmp     esi, edi                ! copy up or down?
        jb      vvc_down
vvc_up:
        cld                             ! direction is up
vvc_uploop:
        and     esi, (_vid_mask)        ! wrap addresses
        and     edi, (_vid_mask)
        mov     ecx, edx                ! one chunk to copy
        mov     eax, (_vid_size)
        sub     eax, esi
        cmp     ecx, eax
        jbe     0f
        mov     ecx, eax                ! ecx = min(ecx, vid_size - esi)
0:      mov     eax, (_vid_size)
        sub     eax, edi
        cmp     ecx, eax
        jbe     0f
        mov     ecx, eax                ! ecx = min(ecx, vid_size - edi)
0:      sub     edx, ecx                ! count -= ecx
        call    vvc_copy                ! copy video words
        test    edx, edx
        jnz     vvc_uploop              ! again?
        jmp     vvc_done
vvc_down:
        std                             ! direction is down
        lea     esi, -1(esi)(edx*1)     ! start copying at the top
        lea     edi, -1(edi)(edx*1)
vvc_downloop:
        and     esi, (_vid_mask)        ! wrap addresses
        and     edi, (_vid_mask)
        mov     ecx, edx                ! one chunk to copy
        lea     eax, 1(esi)
        cmp     ecx, eax
        jbe     0f
        mov     ecx, eax                ! ecx = min(ecx, esi + 1)
0:      lea     eax, 1(edi)
        cmp     ecx, eax
        jbe     0f
        mov     ecx, eax                ! ecx = min(ecx, edi + 1)
0:      sub     edx, ecx                ! count -= ecx
        call    vvc_copy
        test    edx, edx
        jnz     vvc_downloop            ! again?
        cld                             ! C compiler expects up
        !jmp    vvc_done
vvc_done:
        pop     es
        pop     edi
        pop     esi
        pop     ebp
        ret

! Copy video words.  (Inner code of both the up and downcopying loop.)
vvc_copy:
        shl     esi, 1
        shl     edi, 1                  ! byte addresses
        add     esi, (_vid_off)
        add     edi, (_vid_off)         ! in video memory
        rep
eseg o16 movs                           ! copy video words
        sub     esi, (_vid_off)
        sub     edi, (_vid_off)
        shr     esi, 1
        shr     edi, 1                  ! back to word addresses
        ret