source: xtideuniversalbios/trunk/Assembly_Library/Src/Display/DisplayCharOut.asm @ 42

; File name     :   DisplayCharOut.asm
; Project name  :   Assembly Library
; Created date  :   26.6.2010
; Last update   :   18.9.2010
; Author        :   Tomi Tilli
; Description   :   Functions for outputting characters to video memory.
;                   These functions are meant to be called by Display_CharacterFromAL
;                   and Display_RepeatCharacterFromAL using function pointer
;                   stored in DISPLAY_CONTEXT.

; Section containing code
SECTION .text

;--------------------------------------------------------------------
; WAIT_RETRACE_IF_NECESSARY_THEN
;   Parameters:
;       AL:     Character to output
;       AH:     Attribute to output (stosw only)
;       DS:     BDA segment (zero)
;       ES:DI:  Ptr to video memory where to output
;   Returns:
;       DI:     Incremented for next character
;   Corrupts registers:
;       AX, DX
;--------------------------------------------------------------------
%macro WAIT_RETRACE_IF_NECESSARY_THEN 1
%ifdef ELIMINATE_CGA_SNOW
    %ifidn %1, stosb
        call    StosbWithoutCgaSnow
    %else
        call    StoswWithoutCgaSnow
    %endif
%else
    %1          ; STOSB or STOSW
%endif
%endmacro


;--------------------------------------------------------------------
; DisplayCharOut_TeletypeOutputWithAttribute
; DisplayCharOut_TeletypeOutput
;   Parameters:
;       AL:     Character to output
;       AH:     Attribute to output
;       DS:     BDA segment (zero)
;       ES:DI:  Ptr to video memory where to output
;   Returns:
;       DI:     Incremented for next character
;   Corrupts registers:
;       AX, DX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DisplayCharOut_TeletypeOutputWithAttribute:
    cmp     al, ' '                         ; Printable character?
    jb      SHORT DisplayCharOut_BiosTeletypeOutput
    WAIT_RETRACE_IF_NECESSARY_THEN stosw
    ret

ALIGN JUMP_ALIGN
DisplayCharOut_TeletypeOutput:
    cmp     al, ' '                         ; Printable character?
    jae     SHORT DisplayCharOut_Character
    ; Fall to DisplayCharOut_BiosTeletypeOutput

;--------------------------------------------------------------------
; DisplayCharOut_BiosTeletypeOutput
;   Parameters:
;       AL:     Control character
;       DS:     BDA segment (zero)
;       ES:DI:  Ptr to video memory where to output
;   Returns:
;       DI:     Incremented for next character
;   Corrupts registers:
;       AX, DX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DisplayCharOut_BiosTeletypeOutput:
    push    ax
    call    DisplayCursor_SynchronizeCoordinatesToHardware
    pop     ax
    call    .OutputCharacterWithBIOS
    call    DisplayCursor_GetHardwareCoordinatesToAX
    jmp     DisplayCursor_SetCoordinatesFromAX

;--------------------------------------------------------------------
; .OutputCharacterWithBIOS
;   Parameters:
;       AL:     Character to output
;       DS:     BDA segment
;   Returns:
;       Nothing
;   Corrupts registers:
;       AX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
.OutputCharacterWithBIOS:
    push    bx
    mov     ah, TELETYPE_OUTPUT
    mov     bh, [VIDEO_BDA.bActivePage]
    int     BIOS_VIDEO_INTERRUPT_10h
    pop     bx
    ret


;--------------------------------------------------------------------
; DisplayCharOut_Attribute
; DisplayCharOut_Character
; DisplayCharOut_CharacterWithAttribute
;   Parameters:
;       AL:     Character to output
;       AH:     Attribute to output
;       DS:     BDA segment (zero)
;       ES:DI:  Ptr to video memory where to output
;   Returns:
;       DI:     Incremented for next character
;   Corrupts registers:
;       AX, DX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DisplayCharOut_Attribute:
    xchg    al, ah              ; Swap character and attribute
    inc     di                  ; Skip character
    WAIT_RETRACE_IF_NECESSARY_THEN stosb
    ret

ALIGN JUMP_ALIGN
DisplayCharOut_Character:
    WAIT_RETRACE_IF_NECESSARY_THEN stosb
    inc     di                  ; Skip attribute
    ret

ALIGN JUMP_ALIGN
DisplayCharOut_CharacterWithAttribute:
    WAIT_RETRACE_IF_NECESSARY_THEN stosw
    ret


;--------------------------------------------------------------------
; DisplayCharOut_WriteCharacterToBuffer
;   Parameters:
;       AL:     Character to output
;       DS:     BDA segment (zero)
;       ES:DI:  Ptr to destination string buffer
;       DISPLAY_CONTEXT.wCharOutParam:  Offset to end of buffer (one past last)
;   Returns:
;       ES:DI:  Updated for next character
;   Corrupts registers:
;       AX, DX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
DisplayCharOut_WriteCharacterToBuffer:
    cmp     di, [VIDEO_BDA.displayContext+DISPLAY_CONTEXT.wCharOutParam]
    jae     SHORT .BufferFull
    stosb
.BufferFull:
    ret


; STOSB and STOSW replacement functions to prevent CGA snow. These will slow
; drawing a lot so use them only if it is necessary to eliminate CGA snow.
%ifdef ELIMINATE_CGA_SNOW

OFFSET_TO_CGA_STATUS_REGISTER   EQU     6       ; Base port 3D4h + 6 = 3DAh
CGA_STATUS_REGISTER             EQU     3DAh

;--------------------------------------------------------------------
; WAIT_UNTIL_SAFE_CGA_WRITE
;   Parameters:
;       DX:     CGA Status Register Address (3DAh)
;   Returns:
;       Interrupts disabled
;   Corrupts registers:
;       AL
;--------------------------------------------------------------------
%macro WAIT_UNTIL_SAFE_CGA_WRITE 0
    cli             ; Interrupt request would mess up timing
%%WaitUntilNotInRetrace:
    in      al, dx
    shr     al, 1   ; 1 = Bit 0: A 1 indicates that regen-buffer memory access can be
                    ; made without interfering with the display. (H or V retrace)
    jc      SHORT %%WaitUntilNotInRetrace
    sti
    nop             ; Should have time to serve IRQ here
    cli
%%WaitUntilNextRetraceStarts:
    in      al, dx
    shr     al, 1
    jnc     SHORT %%WaitUntilNextRetraceStarts
%endmacro

;--------------------------------------------------------------------
; StosbWithoutCgaSnow
; StoswWithoutCgaSnow
;   Parameters:
;       AL:     Character to output
;       AH:     Attribute to output (StoswWithoutCgaSnow only)
;       DS:     BDA segment (zero)
;       ES:DI:  Ptr to video memory where to output
;   Returns:
;       DI:     Incremented for next character
;   Corrupts registers:
;       AX, DX
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
StosbWithoutCgaSnow:
    call    LoadAndVerifyStatusRegisterFromBDA
    jne     SHORT .StosbWithoutWaitSinceUnknownPort

    mov     ah, al
    WAIT_UNTIL_SAFE_CGA_WRITE
    mov     al, ah
    stosb
    sti
    ret
ALIGN JUMP_ALIGN
.StosbWithoutWaitSinceUnknownPort:
    stosb
    ret

ALIGN JUMP_ALIGN
StoswWithoutCgaSnow:
    call    LoadAndVerifyStatusRegisterFromBDA
    jne     SHORT .StoswWithoutWaitSinceUnknownPort

    push    bx
    xchg    bx, ax
    WAIT_UNTIL_SAFE_CGA_WRITE
    xchg    ax, bx
    stosw
    pop     bx
    sti
    ret
ALIGN JUMP_ALIGN
.StoswWithoutWaitSinceUnknownPort:
    stosw
    ret

;--------------------------------------------------------------------
; LoadAndVerifyStatusRegisterFromBDA
;   Parameters:
;       DS:     BDA segment (zero)
;   Returns:
;       DX:     CGA Status Register Address
;       ZF:     Set if CGA Base Port found in BDA
;   Corrupts registers:
;       Nothing
;--------------------------------------------------------------------
ALIGN JUMP_ALIGN
LoadAndVerifyStatusRegisterFromBDA:
    mov     dx, [BDA.wVidPort]
    add     dl, OFFSET_TO_CGA_STATUS_REGISTER
    cmp     dx, CGA_STATUS_REGISTER
    ret

%endif ; ELIMINATE_CGA_SNOW