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nasmhead.asm
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nasmhead.asm
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; nasmhead.asm
VBEMODE EQU 0x105 ; 1024 x 768 x 8bit
; 0x100 : 640 x 400 x 8bit
; 0x101 : 640 x 480 x 8bit
; 0x103 : 800 x 600 x 8bit
; 0x105 : 1024 x 768 x 8bit
; 0x107 : 1280 x 1024 x 8bit
BOTPAK EQU 0x00280000 ; Load destination of bootpack
DSKCAC EQU 0x00100000 ; Disk cache destination
DSKCAC0 EQU 0x00008000 ; Disk cache destination (Real mode)
; Boot information
CYLS EQU 0x0ff0
LEDS EQU 0x0ff1
VMODE EQU 0x0ff2 ; Color information
SCRNX EQU 0x0ff4 ; Screen X
SCRNY EQU 0x0ff6 ; Screen Y
VRAM EQU 0x0ff8 ; Start number of graphic buffer
ORG 0xc200 ; Where to read this code
MOV AX, 0x9000
MOV ES, AX
MOV DI, 0
MOV AX, 0x4f00
INT 0x10
CMP AX, 0x004f
JNE scrn320
MOV AX, [ES:DI+4]
CMP AX, 0x0200
JB scrn320 ; if (AX < 0x0200) goto scrn320
MOV CX, VBEMODE
MOV AX, 0x4f01
INT 0x10
CMP AX, 0x004f
JNE scrn320
CMP BYTE [ES:DI+0x19], 8
JNE scrn320
CMP BYTE [ES:DI+0x1b], 4
JNE scrn320
MOV AX, [ES:DI+0x00]
AND AX, 0x0080
JZ scrn320
MOV BX, VBEMODE+0x4000
MOV AX, 0x4f02
INT 0x10
MOV BYTE [VMODE], 8
MOV AX, [ES:DI+0x12]
MOV [SCRNX], AX
MOV AX, [ES:DI+0x14]
MOV [SCRNY], AX
MOV EAX, [ES:DI+0x28]
MOV [VRAM], EAX
JMP keystatus
scrn320:
MOV AL, 0x13
MOV AH, 0x00
INT 0x10
MOV BYTE [VMODE], 8
MOV WORD [SCRNX], 320
MOV WORD [SCRNY], 200
MOV DWORD [VRAM], 0x000a0000
keystatus:
MOV AH, 0x02
INT 0x16 ; keyboard BIOS
MOV [LEDS], AL
; PICが一切の割り込みを受け付けないようにする
; AT互換機の仕様では、PICの初期化をする場合、割り込み禁止をCLI前に行わないと、
; たまにハングアップする
; PICの初期化はあとで
MOV AL, 0x0ff
OUT 0x21, AL
NOP
OUT 0xa1, AL
CLI ; Clear interrupt flag
; Settings to access memories over 1MB from CPU
CALL waitkbdout
MOV AL, 0xd1
OUT 0x64, AL
CALL waitkbdout
MOV AL, 0xdf ; Enable A20
OUT 0x60, AL
CALL waitkbdout
; Move protect mode to use i486 instruction set
LGDT [GDTR0]
MOV EAX, CR0
AND EAX, 0x7fffffff ; Set bit31 to 0 not to allow paging
OR EAX, 0x00000001 ; Set bit0 to 1 to move protect mode
MOV CR0, EAX
JMP pipelineflush
pipelineflush:
MOV AX, 1*8 ; read-write 32bit segments
MOV DS, AX
MOV ES, AX
MOV FS, AX
MOV GS, AX
MOV SS, AX
; Send bootpack
MOV ESI, bootpack ; Source
MOV EDI, BOTPAK ; Destination
MOV ECX, 512*1024/4
CALL memcpy
; Send disk data
; Send boot sector
MOV ESI, 0x7c00 ; Source
MOV EDI, DSKCAC ; Destination
MOV ECX, 512/4
CALL memcpy
; All of remainings
MOV ESI, DSKCAC0+512 ; Source
MOV EDI, DSKCAC+512 ; Destination
MOV ECX, 0
MOV CL, BYTE [CYLS]
IMUL ECX, 512*18*2/4 ; To convert from number of cylinders to bite/4
SUB ECX, 512/4 ; Minus IPL
CALL memcpy
; Fin asmhead
; Start bootpack
MOV EBX, BOTPAK
MOV ECX, [EBX+16]
ADD ECX, 3 ; ECX += 3
SHR ECX, 2 ; ECX /= 4
JZ skip ; No things to send
MOV ESI, [EBX+20] ; Source
ADD ESI, EBX
MOV EDI, [EBX+12] ; Destination
CALL memcpy
skip:
MOV ESP, [EBX+12] ; Initial value of stack
JMP DWORD 2*8:0x0000001b
waitkbdout:
IN AL, 0x64
AND AL, 0x02
JNZ waitkbdout
RET
memcpy:
MOV EAX, [ESI]
ADD ESI, 4
MOV [EDI], EAX
ADD EDI, 4
SUB ECX, 1
JNZ memcpy ; Move memcpy if a result is not 0
RET
ALIGNB 16
GDT0:
RESB 8
DW 0xffff, 0x0000, 0x9200, 0x00cf ; Read-write segment 32bits
DW 0xffff, 0x0000, 0x9a28, 0x0047 ; Execuable segment 32bits for bootpack
DW 0
GDTR0:
DW 8*3-1
DD GDT0
ALIGNB 16
bootpack: