62 lines
1.5 KiB
ArmAsm
62 lines
1.5 KiB
ArmAsm
.code16 # tell the assembler that we're using 16 bit mode
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.include "gdt.s"
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.section .text
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.global init # makes our label "init" available to the outside
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.globl mainentry
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init: # this is the beginning of our binary later.
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#jmp init # jump to "init"
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#ljmpw $0xFFFF, $0 # jumps to the "reset vector", doing a reboot
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call printhelloworld
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jmp switchto32bit
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switchto32bit:
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# Load Global Descriptor Table
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lgdt gdt32ptr
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# Load Control Register CR0
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# Enable Protected Mode (Bit0 in CR0)
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# Store Control Register CR0
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movl %cr0, %eax
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orl $(1<<0), %eax
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movl %eax, %cr0
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# Setup all Segment Registers
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# and reload Code Segment, Instruction Pointer
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movw $0x0010, %ax
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movw %ax, %ds
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movw %ax, %es
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movw %ax, %fs
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movw %ax, %gs
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movw %ax, %ss
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ljmp $0x0008, $JumpToPM
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.code32
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JumpToPM:
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call mainentry
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ljmpw $0xFFFF, $0 # jumps to the "reset vector", doing a reboot
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printhelloworld:
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mov $0x0e, %ah # function mode -> display char
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mov $'S', %al
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int $0x10 # video bios interrupt
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mov $'T', %al
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int $0x10 # video bios interrupt
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mov $'A', %al
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int $0x10 # video bios interrupt
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mov $'R', %al
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int $0x10 # video bios interrupt
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mov $'T', %al
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int $0x10 # video bios interrupt
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.fill 510-(.-init), 1, 0 # add zeroes to make it 510 bytes long
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# . is current position - start position
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.word 0xaa55 # magic bytes that tell BIOS that this is bootable
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# x86 is little endian - so bytes are swapped in memory!
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