VESA不適用於BOCHS

Question

我編寫了一個簡單的引導程序，該引導程序設置了視頻模式，並放置了一些像素。 我已經在虛擬盒子，QEMU，Dosbox和真實硬件上對其進行了測試。 對它們有效，但對Bochs無效。 模式設置正確，但未繪制像素。

 org 0x7c00

[BITS 16]           ;Tell Assembler to generate 16-bit code

jmp short start         ;Goto start, skip BIOS-Parameter-Block
nop             

;------------BIOS Parameter Block---------------;
;         Needed to recognize the disk      ;
;-----------------------------------------------;
OEMName:        db 'TEST OS '   ;Name of Orignal Equipment Manufacturer
bytesPerSector:     dw 512      ;Number of bytes in each sector
sectPerCluster:     db 1        ;Sectors in one cluster, 1 for FAT12
reservedCluster:    dw 1        ;1 sector is reserved for boot
totalFATs:      db 2        ;There are 2 fats in FAT12 these are copies of each other
rootDirEntries:     dw 224      ;Total entries (files or folders) in root directory
totalSectors:       dw 2880     ;Total Sectors in whole disk
mediaType:      db 0xf0     ;Media type 240 for floppies
sectorsPerFAT:      dw 9        ;Sectors used in on FAT
sectorsPerTrack:    dw 18       ;Sectors in one Track
totalHeads:     dw 2        ;Total sides of disk
hiddenSectors:      dd 0        
hugeSectors:        dd 0
driveNumber:        db 0        ;Drive Number 0 for A:\ floppy
            db 0
signature:      db 41       ;41 for floppies
volumeID:       dd 0        ;Any number
volumeLabel:        db 'TEST OS    ';Any 11-char name
fileSystem:     db 'FAT12   '   ;Type of file system on disk
;------------------------------------------------


;_______________________________________________

gdt:    dd 0x00000000,0x00000000 ;null descriptor
    dd 0x0000ffff,0x00cf9a00 ;code
    dd 0x0000ffff,0x00cf9200

gdtreg: dw 0x17          ;gdt size + 1
    dd 0             ;gdt base (latter filled)

start:
mov ax,0x4f01 ;get vesa mode info
mov cx,0115h ;video mode number
mov di,modeblock
int 0x10
mov esi, [modeblock+0x28] ;save linear frame buffer base = es:di+0x28

mov ax,0x4f02 ;set vesa mode
mov bx,0115h ;video mode number
int 0x10

mov ax,0x2401
int 0x15    ;enable a20 gate

xor eax,eax
mov ax,cs   
shl eax,4
mov [gdt+0x08+2],ax
shr eax,16
mov [gdt+0x20+4],al


xor eax,eax
mov ax,cs
shl eax,4
add eax,gdt
mov [gdtreg+2],eax
lgdt[gdtreg]

mov eax,cr0
or eax,1

cli
mov cr0,eax
jmp 0x08:pstart

[bits 32]
pstart:
mov eax,0x10
mov es,ax
mov ds,ax
mov fs,ax
mov ss,ax
mov gs,ax


cls:
mov eax,0xffffffff
mov edi, esi
mov ecx,1024*768*1/2
cld
rep stosd

;************ THIS PART IS NOT WORKING ON BOCHS. ************
main:
;test code
mov edi,esi 

mov byte[edi],0x00
inc edi
mov byte[edi],0x00
inc edi
mov byte[edi],0xff
inc edi
mov byte[edi],0x00
inc edi

mov byte[edi],0x00
inc edi
mov byte[edi],0xff
inc edi
mov byte[edi],0x00
inc edi
mov byte[edi],0x00
inc edi

mov byte[edi],0xff
inc edi
mov byte[edi],0x00
inc edi
mov byte[edi],0x00
inc edi
mov byte[edi],0x00
inc edi  

mov byte[edi],0x00
inc edi
mov byte[edi],0x00
inc edi
mov byte[edi],0xff
inc edi
mov byte[edi],0x00
inc edi

mov byte[edi],0x00
inc edi
mov byte[edi],0xff
inc edi
mov byte[edi],0x00
inc edi
mov byte[edi],0x00
inc edi

jmp $

times 510-($-$$) db 0
dw 0xaa55

modeblock:

有什么建議么？ 謝謝。

Answer 1

為了獲得線性幀緩沖，您需要通過將BX寄存器中的位14設置為4F02功能來請求它。 Bochs似乎對此很挑剔，並且如果您尚未啟用線性幀緩沖區，則默默地忽略寫入操作：

if (BX_VGA_THIS vbe.lfb_enabled)
{
...
}
else
{
    if (addr < BX_VGA_THIS vbe.base_address) {
      // banked mode write
      offset = (Bit32u)(BX_VGA_THIS vbe.bank*65536 + (addr - 0xA0000));
    }
    else {
      // LFB write while in banked mode -> ignore
      return;
    }

還要注意，您不應該對模式編號進行硬編碼，因為它們在不同系統上可能會有所不同。 目前尚不清楚您要設置哪種模式，bochs認為0x115是800x600x24，但是您的代碼具有1024*768*1/2 ，這暗示的不是您所期望的。

Answer 2

為了使用VESA VBE，您需要通過將vga選項設置為vbe在bochsrc中啟用它。 http://bochs.sourceforge.net/doc/docbook/user/vesa-notes.html

vesa.org的vbe3.pdf

VBE退貨狀態

AL == 4Fh: Function is supported
AL != 4Fh: Function is not supported
AH == 00h: Function call successful
AH == 01h: Function call failed
AH == 02h: Function is not supported in the current hardware configuration
AH == 03h: Function call invalid in current video mode

VBE模式編號的格式如下：

D0-D8 = Mode number
If D8 == 0, this is not a VESA defined VBE mode
If D8 == 1, this is a VESA defined VBE mode
D9-D12 = Reserved by VESA for future expansion (= 0)
D11 = Refresh Rate Control Select
If D11 == 0, Use current BIOS default refresh rate
If D11 == 1, Use user specified CRTC values for refresh rate
D12-13 = Reserved for VBE/AF (must be 0)
D14 = Linear/Flat Frame Buffer Select
If D14 == 0, Use Banked/Windowed Frame Buffer
If D14 == 1, Use Linear/Flat Frame Buffer
D15 = Preserve Display Memory Select
If D15 == 0, Clear display memory
If D15 == 1, Preserve display memory