Initial checkin of toy OS project.HEADmaster

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"
+        
+        
\ No newline at end of file