/////////////////////////////////////////// boot.s
! boot.s
!
! It then loads the system at 0x10000, using BIOS interrupts. Thereafter
! it disables all interrupts, changes to protected mode, and calls the
BOOTSEG = 0x07c0
SYSSEG = 0x1000 ! system loaded at 0x10000 (65536).
SYSLEN = 17 ! sectors occupied.
entry start
start:
jmpi go,#BOOTSEG
go: mov ax,cs
mov ds,ax
mov ss,ax
mov sp,#0x400 ! arbitrary value >>512
! ok, we've written the message, now
load_system:
mov dx,#0x0000
mov cx,#0x0002
mov ax,#SYSSEG
mov es,ax
xor bx,bx
mov ax,#0x200+SYSLEN
int 0x13
jnc ok_load
die: jmp die
! now we want to move to protected mode ...
ok_load:
cli ! no interrupts allowed !
mov ax, #SYSSEG
mov ds, ax
xor ax, ax
mov es, ax
mov cx, #0x2000
sub si,si
sub di,di
rep
movw
mov ax, #BOOTSEG
mov ds, ax
lidt idt_48 ! load idt with 0,0
lgdt gdt_48 ! load gdt with whatever appropriate
! absolute address 0x00000, in 32-bit protected mode.
mov ax,#0x0001 ! protected mode (PE) bit
lmsw ax ! This is it!
jmpi 0,8 ! jmp offset 0 of segment 8 (cs)
gdt: .word 0,0,0,0 ! dummy
.word 0x07FF ! 8Mb - limit=2047 (2048*4096=8Mb)
.word 0x0000 ! base address=0x00000
.word 0x9A00 ! code read/exec
.word 0x00C0 ! granularity=4096, 386
.word 0x07FF ! 8Mb - limit=2047 (2048*4096=8Mb)
.word 0x0000 ! base address=0x00000
.word 0x9200 ! data read/write
.word 0x00C0 ! granularity=4096, 386
idt_48: .word 0 ! idt limit=0
.word 0,0 ! idt base=0L
gdt_48: .word 0x7ff ! gdt limit=2048, 256 GDT entries
.word 0x7c00+gdt,0 ! gdt base = 07xxx
.org 510
.word 0xAA55
/////////////////////////////////////////// end of boot.s
/////////////////////////////////////////// head.s
# head.s contains the 32-bit startup code.
# Two L3 task multitasking. The code of tasks are in kernel area,
# just like the Linux. The kernel code is located at 0x10000.
SCRN_SEL = 0x18
TSS0_SEL = 0x20
LDT0_SEL = 0x28
TSS1_SEL = 0X30
LDT1_SEL = 0x38
.text
startup_32:
movl $0x10,%eax
mov %ax,%ds
# mov %ax,%es
lss init_stack,%esp
# setup base fields of descriptors.
call setup_idt
call setup_gdt
movl $0x10,%eax # reload all the segment registers
mov %ax,%ds # after changing gdt.
mov %ax,%es
mov %ax,%fs
mov %ax,%gs
lss init_stack,%esp
# setup up timer 8253 chip.
movb $0x36, %al
movl $0x43, %edx
outb %al, %dx
movl $11930, %eax # timer frequency 100 HZ
movl $0x40, %edx
outb %al, %dx
movb %ah, %al
outb %al, %dx
# setup timer & system call interrupt descriptors.
movl $0x00080000, %eax
movw $timer_interrupt, %ax
movw $0x8E00, %dx
movl $0x08, %ecx # The PC default timer int.
lea idt(,%ecx,8), %esi
movl %eax,(%esi)
movl %edx,4(%esi)
movw $system_interrupt, %ax
movw $0xef00, %dx
movl $0x80, %ecx
lea idt(,%ecx,8), %esi
movl %eax,(%esi)
movl %edx,4(%esi)
# unmask the timer interrupt.
# movl $0x21, %edx
# inb %dx, %al
# andb $0xfe, %al
# outb %al, %dx
# Move to user mode (task 0)
pushfl
andl $0xffffbfff, (%esp)
popfl
movl $TSS0_SEL, %eax
ltr %ax
movl $LDT0_SEL, %eax
lldt %ax
movl $0, current
sti
pushl $0x17
pushl $init_stack
pushfl
pushl $0x0f
pushl $task0
iret
/****************************************/
setup_gdt:
lgdt lgdt_opcode
ret
setup_idt:
lea ignore_int,%edx
movl $0x00080000,%eax
movw %dx,%ax /* selector = 0x0008 = cs */
movw $0x8E00,%dx /* interrupt gate - dpl=0, present */
lea idt,%edi
mov $256,%ecx
rp_sidt:
movl %eax,(%edi)
movl %edx,4(%edi)
addl $8,%edi
dec %ecx
jne rp_sidt
lidt lidt_opcode
ret
# -----------------------------------
write_char:
push %gs
pushl %ebx
# pushl %eax
mov $SCRN_SEL, %ebx
mov %bx, %gs
movl scr_loc, %bx
shl $1, %ebx
movb %al, %gs:(%ebx)
shr $1, %ebx
incl %ebx
cmpl $2000, %ebx
jb 1f
movl $0, %ebx
1: movl %ebx, scr_loc
# popl %eax
popl %ebx
pop %gs
ret
/***********************************************/
/* This is the default interrupt "handler" :-) */
.align 2
ignore_int:
push %ds
pushl %eax
movl $0x10, %eax
mov %ax, %ds
movl $67, %eax /* print 'C' */
call write_char
popl %eax
pop %ds
iret
/* Timer interrupt handler */
.align 2
timer_interrupt:
push %ds
pushl %eax
movl $0x10, %eax
mov %ax, %ds
movb $0x20, %al
outb %al, $0x20
movl $1, %eax
cmpl %eax, current
je 1f
movl %eax, current
ljmp $TSS1_SEL, $0
jmp 2f
1: movl $0, current
ljmp $TSS0_SEL, $0
2: popl %eax
pop %ds
iret
/* system call handler */
.align 2
system_interrupt:
push %ds
pushl %edx
pushl %ecx
pushl %ebx
pushl %eax
movl $0x10, %edx
mov %dx, %ds
call write_char
popl %eax
popl %ebx
popl %ecx
popl %edx
pop %ds
iret
/*********************************************/
current:.long 0
scr_loc:.long 0
.align 2
lidt_opcode:
.word 256*8-1 # idt contains 256 entries
.long idt # This will be rewrite by code.
lgdt_opcode:
.word (end_gdt-gdt)-1 # so does gdt
.long gdt # This will be rewrite by code.
.align 3
idt: .fill 256,8,0 # idt is uninitialized
gdt: .quad 0x0000000000000000 /* NULL descriptor */
.quad 0x00c09a00000007ff /* 8Mb 0x08, base = 0x00000 */
.quad 0x00c09200000007ff /* 8Mb 0x10 */
.quad 0x00c0920b80000002 /* screen 0x18 - for display */
.word 0x0068, tss0, 0xe900, 0x0 # TSS0 descr 0x20
.word 0x0040, ldt0, 0xe200, 0x0 # LDT0 descr 0x28
.word 0x0068, tss1, 0xe900, 0x0 # TSS1 descr 0x30
.word 0x0040, ldt1, 0xe200, 0x0 # LDT1 descr 0x38
end_gdt:
.fill 128,4,0
init_stack: # Will be used as user stack for task0.
.long init_stack
.word 0x10
/*************************************/
.align 3
ldt0: .quad 0x0000000000000000
.quad 0x00c0fa00000003ff # 0x0f, base = 0x00000
.quad 0x00c0f200000003ff # 0x17
tss0: .long 0 /* back link */
.long krn_stk0, 0x10 /* esp0, ss0 */
.long 0, 0, 0, 0, 0 /* esp1, ss1, esp2, ss2, cr3 */
.long 0, 0, 0, 0, 0 /* eip, eflags, eax, ecx, edx */
.long 0, 0, 0, 0, 0 /* ebx esp, ebp, esi, edi */
.long 0, 0, 0, 0, 0, 0 /* es, cs, ss, ds, fs, gs */
.long LDT0_SEL, 0x8000000 /* ldt, trace bitmap */
.fill 128,4,0
krn_stk0:
# .long 0
/************************************/
.align 3
ldt1: .quad 0x0000000000000000
.quad 0x00c0fa00000003ff # 0x0f, base = 0x00000
.quad 0x00c0f200000003ff # 0x17
tss1: .long 0 /* back link */
.long krn_stk1, 0x10 /* esp0, ss0 */
.long 0, 0, 0, 0, 0 /* esp1, ss1, esp2, ss2, cr3 */
.long task1, 0x200 /* eip, eflags */
.long 0, 0, 0, 0 /* eax, ecx, edx, ebx */
.long usr_stk1, 0, 0, 0 /* esp, ebp, esi, edi */
.long 0x17,0x0f,0x17,0x17,0x17,0x17 /* es, cs, ss, ds, fs, gs */
.long LDT1_SEL, 0x8000000 /* ldt, trace bitmap */
.fill 128,4,0
krn_stk1:
/************************************/
task0:
movl $0x17, %eax
movw %ax, %ds
movl $65, %al /* print 'A' */
int $0x80
movl $0xfff, %ecx
1: loop 1b
jmp task0
task1:
movl $0x17, %eax
movw %ax, %ds
movl $66, %al /* print 'B' */
int $0x80
movl $0xfff, %ecx
1: loop 1b
jmp task1
.fill 128,4,0
usr_stk1:
/////////////////////////////////////////// end of head.s |
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