diff options
Diffstat (limited to 'bootasm.S')
| -rw-r--r-- | bootasm.S | 88 |
1 files changed, 0 insertions, 88 deletions
diff --git a/bootasm.S b/bootasm.S deleted file mode 100644 index 257867c..0000000 --- a/bootasm.S +++ /dev/null @@ -1,88 +0,0 @@ -#include "asm.h" -#include "memlayout.h" -#include "mmu.h" - -# Start the first CPU: switch to 32-bit protected mode, jump into C. -# The BIOS loads this code from the first sector of the hard disk into -# memory at physical address 0x7c00 and starts executing in real mode -# with %cs=0 %ip=7c00. - -.code16 # Assemble for 16-bit mode -.globl start -start: - cli # BIOS enabled interrupts; disable - - # Zero data segment registers DS, ES, and SS. - xorw %ax,%ax # Set %ax to zero - movw %ax,%ds # -> Data Segment - movw %ax,%es # -> Extra Segment - movw %ax,%ss # -> Stack Segment - - # Physical address line A20 is tied to zero so that the first PCs - # with 2 MB would run software that assumed 1 MB. Undo that. -seta20.1: - inb $0x64,%al # Wait for not busy - testb $0x2,%al - jnz seta20.1 - - movb $0xd1,%al # 0xd1 -> port 0x64 - outb %al,$0x64 - -seta20.2: - inb $0x64,%al # Wait for not busy - testb $0x2,%al - jnz seta20.2 - - movb $0xdf,%al # 0xdf -> port 0x60 - outb %al,$0x60 - - # Switch from real to protected mode. Use a bootstrap GDT that makes - # virtual addresses map directly to physical addresses so that the - # effective memory map doesn't change during the transition. - lgdt gdtdesc - movl %cr0, %eax - orl $CR0_PE, %eax - movl %eax, %cr0 - -//PAGEBREAK! - # Complete the transition to 32-bit protected mode by using a long jmp - # to reload %cs and %eip. The segment descriptors are set up with no - # translation, so that the mapping is still the identity mapping. - ljmp $(SEG_KCODE<<3), $start32 - -.code32 # Tell assembler to generate 32-bit code now. -start32: - # Set up the protected-mode data segment registers - movw $(SEG_KDATA<<3), %ax # Our data segment selector - movw %ax, %ds # -> DS: Data Segment - movw %ax, %es # -> ES: Extra Segment - movw %ax, %ss # -> SS: Stack Segment - movw $0, %ax # Zero segments not ready for use - movw %ax, %fs # -> FS - movw %ax, %gs # -> GS - - # Set up the stack pointer and call into C. - movl $start, %esp - call bootmain - - # If bootmain returns (it shouldn't), trigger a Bochs - # breakpoint if running under Bochs, then loop. - movw $0x8a00, %ax # 0x8a00 -> port 0x8a00 - movw %ax, %dx - outw %ax, %dx - movw $0x8ae0, %ax # 0x8ae0 -> port 0x8a00 - outw %ax, %dx -spin: - jmp spin - -# Bootstrap GDT -.p2align 2 # force 4 byte alignment -gdt: - SEG_NULLASM # null seg - SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff) # code seg - SEG_ASM(STA_W, 0x0, 0xffffffff) # data seg - -gdtdesc: - .word (gdtdesc - gdt - 1) # sizeof(gdt) - 1 - .long gdt # address gdt - |