BIOS使用的视频模式

时间：2014-02-22 12:01:45

标签： graphics operating-system bootloader bios

编写2阶段引导加载程序并查看输出后：

Output from QEMU

第一阶段的输出（使用BIOS'int 10h中断产生）与通过在保护模式下直接访问视频内存获得的白色（或灰色？）不同。

为什么会有所不同？ BIOS使用什么视频模式？

2 个答案:

答案 0 :(得分：2)

BIOS以模式0启动，颜色属性字节为0x07（黑色背景，灰色前景）。第二个白色似乎是0x0F，因为亮位被设置（0x08是亮度位，只需将其添加到颜色以获得鲜艳的颜色）。

答案 1 :(得分：0)

当IBM PC兼容计算机启动时，POST后，当BIOS准备好加载启动加载程序时，BIOS视频模式为3（二进制11）。我已经在几台计算机和Bochs 2.6.8上使用以下引导扇区程序（为FASM编写）对此进行了测试。

;
;
; This boot sector program invokes BIOS INT 10h AH=0Fh (get current video mode) and displays the results to the screen
;
;
  ; Preliminary directives so fasm knows how to generate the machine code
  ;
    format binary                             ; this directive tells fasm to write the generated code as a flat binary file
    use16                                     ; this directive tells fasm to generate 16-bit code
    org 0x7C00                                ; org directive tells fasm that the program will be loaded at 0x7C00, where the BIOS hands over control to the bootstrap code
;
;
  ; Get current video mode (INT 10h, function AH=0Fh)
  ;
    mov ah,0xF                                ; set AH to 0xF (AH=0Fh is the function for getting the current video mode)
    int 0x10                                  ; invoke BIOS interrupt 10h, function AH=0Fh to get the current video mode
;
;
  ; Display results to the screen
  ;
    ; Save the results for printing later
    ;
      mov dh,al                               ; save AL (the current video mode) to DH
      push bx                                 ; save BH to the stack
      push ax                                 ; save AH to the stack
    ;
    ; Display the value saved to DH (i.e. the current video mode, which was copied from AL to DH above)
    ;
      xor ax,ax                               ; set AX to 0 in order to set DS to 0
      mov ds,ax                               ; DS = 0 (SI works with DS to point to the address created by DS:SI)
      mov si,vid_mode_prompt                  ; set SI to point to the first character of the message to be printed
      mov cx,12                               ; set the counter (CX) to match the number of characters to print
      call print_string_procedure             ; save to the stack the address of the next instruction, then jump to the procedure called by this instruction
      call procedure_for_printing_DH          ; save to the stack the address of the next instruction, then jump to the procedure called by this instruction
    ;
    ; Display the value for the number of character columns used by the current video mode (pushed onto the stack from AH)
    ;
      ;xor ax,ax                               ; set AX to 0 in order to set DS to 0 (commented out, because AX is not needed to set DS, since DS is probably already 0)
      ;mov ds,ax                               ; DS = 0 (SI works with DS to point to the address created by DS:SI) (commented out, because DS is probably already 0)
      mov si,num_col_prompt                   ; set SI to point to the first character of the message to be printed
      mov cx,13                               ; set the counter (CX) to match the number of characters to print
      call print_string_procedure             ; save to the stack the address of the next instruction, then jump to the procedure called by this instruction
      pop dx                                  ; copy to DH the number of columns previously saved to the stack from AH
      call procedure_for_printing_DH          ; save to the stack the address of the next instruction, then jump to the procedure called by this instruction
    ;
    ; Display the value for the active display page (pushed onto the stack from BH)
    ;
      ;xor ax,ax                               ; set AX to 0 in order to set DS to 0 (commented out, because AX is not needed to set DS, since DS is probably already 0)
      ;mov ds,ax                               ; DS = 0 (SI works with DS to point to the address created by DS:SI) (commented out, because DS is probably already 0)
      mov si,display_page_prompt              ; set SI to point to the first character of the message to be printed
      mov cx,17                               ; set the counter (CX) to match the number of characters to print
      call print_string_procedure             ; save to the stack the address of the next instruction, then jump to the procedure called by this instruction
      pop dx                                  ; copy to DH the value of the active display page
      call procedure_for_printing_DH          ; save to the stack the address of the next instruction, then jump to the procedure called by this instruction
;
;
  ; End of program
  ;
    end_of_program:                           ; label for this section of code
    hlt                                       ; stops instruction execution and places the processor in a halted state
    jmp end_of_program                        ; jump to the label 'end_of_program'
;
;
  ;
  ;
  ; Procedures called by the program
  ;
  ;
    print_string_procedure:                   ; label for this section of code
    ;pusha                                     ; save all 8 general registers to the stack (commented out, because it is not necessary to save the values of the general registers)
    mov ah,0xE                                ; set AH to 0Eh (i.e. select teletype output)
    xor bh,bh                                 ; set display page number to 0
      start_of_print_loop:                    ; label for this section of code
      lodsb                                   ; load string byte (i.e. copy the string element pointed to by DS:SI to AL)
      int 0x10                                ; invoke BIOS interrupt 10h, function AH=0Eh to display the ASCII character stored in AL
      loop start_of_print_loop                ; decrement CX by 1, then jump to the specified label until CX=0
    ;popa                                      ; pop the contents of all eight general registers back from the stack (commented out, because popa corresponds with pusha, which has been commented out above)
    ret                                       ; transfer control back to the program that invoked the procedure using the address that was stored on the stack by the call instruction
  ;
    procedure_for_printing_DH:                ; label for this section of code
    ;pusha                                     ; save all 8 general registers to the stack (commented out, because it is not necessary to save the values of the general registers)
    ;mov ah,0xE                                ; set AH to 0Eh (i.e. select teletype output) (commented out, because the value in AH is already 0Eh)
    ;xor bh,bh                                 ; set display page number to 0 (commented out, because the value in BH is already 0)
    mov cx,4                                  ; set the counter (CX) to match the number of characters to print
    call start_print_DH_loop                  ; save to the stack the address of the next instruction, then jump to the procedure called by this instruction
    mov al,0x20                               ; set AL to print a space (ASCII code for a space is 0x20)
    int 0x10                                  ; invoke BIOS interrupt 10h, function AH=0Eh to display the ASCII character stored in AL
    mov cx,4                                  ; set the counter (CX) to match the number of characters to print
    call start_print_DH_loop                  ; save to the stack the address of the next instruction, then jump to the procedure called by this instruction
    ;popa                                      ; pop the contents of all eight general registers back from the stack (commented out, because popa corresponds with pusha, which has been commented out above)
    ret                                       ; transfer control back to the program that invoked the procedure using the address that was stored on the stack by the call instruction
  ;
    start_print_DH_loop:                      ; label for this section of code
    shl dh,1                                  ; shifts the bits in the DH register to the left by one bit; the last exited bit will be stored to the CF flag
    setc al                                   ; sets the AL register to match the value of the CF flag
    add al,0x30                               ; convert the number in AL (0 or 1) to ASCII
    int 0x10                                  ; invoke BIOS interrupt 10h, function AH=0Eh to display the ASCII character stored in AL
    loop start_print_DH_loop                  ; decrement CX by 1, then jump to the specified label until CX=0
    ret                                       ; transfer control back to the program that invoked the procedure using the address that was stored on the stack by the call instruction
;
;
  ;
  ;
  ; Data used by the program
  ;
  ;
    vid_mode_prompt:
    db 'Video mode: '                         ; 12 characters
    ;
    num_col_prompt:
    db 0xD,0xA,0xD,0xA,'Columns: '            ; 13 characters
    ;
    display_page_prompt:
    db 0xD,0xA,0xD,0xA,'Active page: '        ; 17 characters
;
;
  ; Padding and magic number
    times 510-($-$$) db 0
    dw 0xaa55

Screenshot from Bochs 2.6.8 after compiling and running the above program

Information from Wikipedia on INT 10H

相关问题
最新问题