0.00-050613_head.s
1 # head.s contains the 32-bit startup code. 2 # Two L3 task multitasking. The code of tasks are in kernel area, 3 # just like the Linux. The kernel code is located at 0x10000. 4 SCRN_SEL = 0x18 5 TSS0_SEL = 0x20 6 LDT0_SEL = 0x28 7 TSS1_SEL = 0X30 8 LDT1_SEL = 0x38 9 10 .text 11 startup_32: 12 movl $0x10,%eax 13 mov %ax,%ds 14 # mov %ax,%es 15 lss init_stack,%esp 16 17 # setup base fields of descriptors. 18 call setup_idt 19 call setup_gdt 20 movl $0x10,%eax # reload all the segment registers 21 mov %ax,%ds # after changing gdt. 22 mov %ax,%es 23 mov %ax,%fs 24 mov %ax,%gs 25 lss init_stack,%esp 26 27 # setup up timer 8253 chip. 28 movb $0x36, %al 29 movl $0x43, %edx 30 outb %al, %dx 31 movl $11930, %eax # timer frequency 100 HZ 32 movl $0x40, %edx 33 outb %al, %dx 34 movb %ah, %al 35 outb %al, %dx 36 37 # setup timer & system call interrupt descriptors. 38 movl $0x00080000, %eax 39 movw $timer_interrupt, %ax 40 movw $0x8E00, %dx 41 movl $0x08, %ecx # The PC default timer int. 42 lea idt(,%ecx,8), %esi 43 movl %eax,(%esi) 44 movl %edx,4(%esi) 45 movw $system_interrupt, %ax 46 movw $0xef00, %dx 47 movl $0x80, %ecx 48 lea idt(,%ecx,8), %esi 49 movl %eax,(%esi) 50 movl %edx,4(%esi) 51 52 # unmask the timer interrupt. 53 # movl $0x21, %edx 54 # inb %dx, %al 55 # andb $0xfe, %al 56 # outb %al, %dx 57 58 # Move to user mode (task 0) 59 pushfl 60 andl $0xffffbfff, (%esp) 61 popfl 62 movl $TSS0_SEL, %eax 63 ltr %ax 64 movl $LDT0_SEL, %eax 65 lldt %ax 66 movl $0, current 67 sti 68 pushl $0x17 69 pushl $init_stack 70 pushfl 71 pushl $0x0f 72 pushl $task0 73 iret 74 75 /****************************************/ 76 setup_gdt: 77 lgdt lgdt_opcode 78 ret 79 80 setup_idt: 81 lea ignore_int,%edx 82 movl $0x00080000,%eax 83 movw %dx,%ax /* selector = 0x0008 = cs */ 84 movw $0x8E00,%dx /* interrupt gate - dpl=0, present */ 85 lea idt,%edi 86 mov $256,%ecx 87 rp_sidt: 88 movl %eax,(%edi) 89 movl %edx,4(%edi) 90 addl $8,%edi 91 dec %ecx 92 jne rp_sidt 93 lidt lidt_opcode 94 ret 95 96 # ----------------------------------- 97 write_char: 98 push %gs 99 pushl %ebx 100 # pushl %eax 101 mov $SCRN_SEL, %ebx 102 mov %bx, %gs 103 movl scr_loc, %bx 104 shl $1, %ebx 105 movb %al, %gs:(%ebx) 106 shr $1, %ebx 107 incl %ebx 108 cmpl $2000, %ebx 109 jb 1f 110 movl $0, %ebx 111 1: movl %ebx, scr_loc 112 # popl %eax 113 popl %ebx 114 pop %gs 115 ret 116 117 /***********************************************/ 118 /* This is the default interrupt "handler" :-) */ 119 .align 2 120 ignore_int: 121 push %ds 122 pushl %eax 123 movl $0x10, %eax 124 mov %ax, %ds 125 movl $67, %eax /* print 'C' */ 126 call write_char 127 popl %eax 128 pop %ds 129 iret 130 131 /* Timer interrupt handler */ 132 .align 2 133 timer_interrupt: 134 push %ds 135 pushl %eax 136 movl $0x10, %eax 137 mov %ax, %ds 138 movb $0x20, %al 139 outb %al, $0x20 140 movl $1, %eax 141 cmpl %eax, current 142 je 1f 143 movl %eax, current 144 ljmp $TSS1_SEL, $0 145 jmp 2f 146 1: movl $0, current 147 ljmp $TSS0_SEL, $0 148 2: popl %eax 149 pop %ds 150 iret 151 152 /* system call handler */ 153 .align 2 154 system_interrupt: 155 push %ds 156 pushl %edx 157 pushl %ecx 158 pushl %ebx 159 pushl %eax 160 movl $0x10, %edx 161 mov %dx, %ds 162 call write_char 163 popl %eax 164 popl %ebx 165 popl %ecx 166 popl %edx 167 pop %ds 168 iret 169 170 /*********************************************/ 171 current:.long 0 172 scr_loc:.long 0 173 174 .align 2 175 lidt_opcode: 176 .word 256*8-1 # idt contains 256 entries 177 .long idt # This will be rewrite by code. 178 lgdt_opcode: 179 .word (end_gdt-gdt)-1 # so does gdt 180 .long gdt # This will be rewrite by code. 181 182 .align 3 183 idt: .fill 256,8,0 # idt is uninitialized 184 185 gdt: .quad 0x0000000000000000 /* NULL descriptor */ 186 .quad 0x00c09a00000007ff /* 8Mb 0x08, base = 0x00000 */ 187 .quad 0x00c09200000007ff /* 8Mb 0x10 */ 188 .quad 0x00c0920b80000002 /* screen 0x18 - for display */ 189 190 .word 0x0068, tss0, 0xe900, 0x0 # TSS0 descr 0x20 191 .word 0x0040, ldt0, 0xe200, 0x0 # LDT0 descr 0x28 192 .word 0x0068, tss1, 0xe900, 0x0 # TSS1 descr 0x30 193 .word 0x0040, ldt1, 0xe200, 0x0 # LDT1 descr 0x38 194 end_gdt: 195 .fill 128,4,0 196 init_stack: # Will be used as user stack for task0. 197 .long init_stack 198 .word 0x10 199 200 /*************************************/ 201 .align 3 202 ldt0: .quad 0x0000000000000000 203 .quad 0x00c0fa00000003ff # 0x0f, base = 0x00000 204 .quad 0x00c0f200000003ff # 0x17 205 206 tss0: .long 0 /* back link */ 207 .long krn_stk0, 0x10 /* esp0, ss0 */ 208 .long 0, 0, 0, 0, 0 /* esp1, ss1, esp2, ss2, cr3 */ 209 .long 0, 0, 0, 0, 0 /* eip, eflags, eax, ecx, edx */ 210 .long 0, 0, 0, 0, 0 /* ebx esp, ebp, esi, edi */ 211 .long 0, 0, 0, 0, 0, 0 /* es, cs, ss, ds, fs, gs */ 212 .long LDT0_SEL, 0x8000000 /* ldt, trace bitmap */ 213 214 .fill 128,4,0 215 krn_stk0: 216 # .long 0 217 218 /************************************/ 219 .align 3 220 ldt1: .quad 0x0000000000000000 221 .quad 0x00c0fa00000003ff # 0x0f, base = 0x00000 222 .quad 0x00c0f200000003ff # 0x17 223 224 tss1: .long 0 /* back link */ 225 .long krn_stk1, 0x10 /* esp0, ss0 */ 226 .long 0, 0, 0, 0, 0 /* esp1, ss1, esp2, ss2, cr3 */ 227 .long task1, 0x200 /* eip, eflags */ 228 .long 0, 0, 0, 0 /* eax, ecx, edx, ebx */ 229 .long usr_stk1, 0, 0, 0 /* esp, ebp, esi, edi */ 230 .long 0x17,0x0f,0x17,0x17,0x17,0x17 /* es, cs, ss, ds, fs, gs */ 231 .long LDT1_SEL, 0x8000000 /* ldt, trace bitmap */ 232 233 .fill 128,4,0 234 krn_stk1: 235 236 /************************************/ 237 task0: 238 movl $0x17, %eax 239 movw %ax, %ds 240 movl $65, %al /* print 'A' */ 241 int $0x80 242 movl $0xfff, %ecx 243 1: loop 1b 244 jmp task0 245 246 task1: 247 movl $0x17, %eax 248 movw %ax, %ds 249 movl $66, %al /* print 'B' */ 250 int $0x80 251 movl $0xfff, %ecx 252 1: loop 1b 253 jmp task1 254 255 .fill 128,4,0 256 usr_stk1:
C
