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Diffstat (limited to 'boot1/boot1.asm')
| -rw-r--r-- | boot1/boot1.asm | 113 |
1 files changed, 113 insertions, 0 deletions
diff --git a/boot1/boot1.asm b/boot1/boot1.asm new file mode 100644 index 0000000..59c0dd0 --- /dev/null +++ b/boot1/boot1.asm @@ -0,0 +1,113 @@ +[BITS 16] +[ORG 0] + +START: + ;; initialize segments + mov ax, BOOT1SEG + mov ds, ax + mov es, ax + mov ss, ax + + ;; make sure we are running on a 386+ + + ;; while we're still in real mode, detect system hardware via BIOS + call PROBE_VIDEO + call GET_EQUIPMENT_LIST + call GET_MEMORY_SIZE + call GET_TIME + + ;; switch the processor into protected mode, keep ints disabled + cli + lidt [IDT_Pointer] + lgdt [GDT_Pointer] + call ENABLE_A20 + mov ax, 0x01 + lmsw ax + + ;; Jump to 32 bit code, this completes the transition to protected mode + db 0x66 ; operand size override prefix + db 0xea ; jmp opcode + dd (BOOT1SEG<<4) + setup_32 ; want to jump here + dw (1<<3) ; ...in the kernel code segment + +[BITS 32] +setup_32: + ;; set up data segment registers + mov ax, (2<<3) + mov ds, ax + mov es, ax + mov fs, ax + mov gs, ax + mov ss, ax + + ;; create an initial stack + mov esp, KERN_STACK + 4096 + mov ebp, esp + + ;; create a stack frame, pass ptr to hardware block as param + mov eax, (BOOT1SEG<<4)+BIOS_HARDWARE_BLOCK + push eax + push (BOOT1SEG<<4)+.HANG + jmp (1<<3):0x00010000 ; entry point of kernel + +.HANG: + nop + jmp .HANG + + +; Setup data +; ---------------------------------------------------------------------- + +BIOS_HARDWARE_BLOCK: +bDisplayType db 0x00 +bFontSize db 0x00 +wEquipmentBitvector dw 0x0000 +wMemorySize dw 0x0000 +wSystemClock dw 0x0000 + +NUM_GDT_ENTRIES equ 3 ; number of entries in GDT +GDT_ENTRY_SZ equ 8 ; size of a single GDT entry + +align 8, db 0 +GDT: + ; Descriptor 0 is not used + dw 0 + dw 0 + dw 0 + dw 0 + + ; Descriptor 1: kernel code segment + dw 0xFFFF ; bytes 0 and 1 of segment size + dw 0x0000 ; bytes 0 and 1 of segment base address + db 0x00 ; byte 2 of segment base address + db 0x9A ; present, DPL=0, non-system, code, non-conforming, + ; readable, not accessed + db 0xCF ; granularity=page, 32 bit code, upper nibble of size + db 0x00 ; byte 3 of segment base address + + ; Descriptor 2: kernel data and stack segment + ; NOTE: what Intel calls an "expand-up" segment + ; actually means that the stack will grow DOWN, + ; towards lower memory. So, we can use this descriptor + ; for both data and stack references. + dw 0xFFFF ; bytes 0 and 1 of segment size + dw 0x0000 ; bytes 0 and 1 of segment base address + db 0x00 ; byte 2 of segment base address + db 0x92 ; present, DPL=0, non-system, data, expand-up, + ; writable, not accessed + db 0xCF ; granularity=page, big, upper nibble of size + db 0x00 ; byte 3 of segment base address + +GDT_Pointer: + dw NUM_GDT_ENTRIES*GDT_ENTRY_SZ ; limit + dd (BOOT1SEG<<4) + GDT ; base address + +IDT_Pointer: + dw 0 + dd 00 + +%include "defs.asm" +%include "hardware.asm" +%include "video.asm" + +
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