Initial commit: SUB-OS 64-Bit Production Monolithic Operating System with LazyBox userland suite

boot/boot.asm

@@ -0,0 +1,98 @@
+BITS 16
+ORG 0x7C00
+
+start:
+    ; Set up segments and stack
+    cli
+    xor ax, ax
+    mov ds, ax
+    mov es, ax
+    mov ss, ax
+    mov sp, 0x7C00
+    sti
+
+    ; Save boot drive number from BIOS (DL)
+    mov [BOOT_DRIVE], dl
+
+    ; Print greeting
+    mov si, MSG_BOOT
+    call print_string
+
+    ; Check for LBA extensions (INT 13h, AH=41h)
+    mov ah, 0x41
+    mov bx, 0x55AA
+    mov dl, [BOOT_DRIVE]
+    int 0x13
+    jc load_chs
+    cmp bx, 0xAA55
+    jne load_chs
+
+load_lba:
+    ; Load stage 2 using LBA (INT 13h, AH=42h)
+    ; Read 15 sectors starting from LBA 1 to 0x0000:0x7E00
+    mov ah, 0x42
+    mov dl, [BOOT_DRIVE]
+    mov si, dap
+    int 0x13
+    jc disk_error
+    jmp jump_stage2
+
+load_chs:
+    ; Fallback: Load stage 2 using CHS (INT 13h, AH=02h)
+    mov ah, 0x02
+    mov al, 15              ; 15 sectors (sectors 2-16)
+    mov ch, 0               ; Cylinder 0
+    mov dh, 0               ; Head 0
+    mov cl, 2               ; Sector 2
+    xor bx, bx
+    mov es, bx
+    mov bx, 0x7E00          ; ES:BX = 0x0000:0x7E00
+    mov dl, [BOOT_DRIVE]
+    int 0x13
+    jc disk_error
+
+jump_stage2:
+    ; Pass boot drive in DL to Stage 2
+    mov dl, [BOOT_DRIVE]
+    jmp 0x0000:0x7E00
+
+disk_error:
+    mov si, MSG_DISK_ERR
+    call print_string
+.halt:
+    cli
+    hlt
+    jmp .halt
+
+; BIOS Teletype string print (SI = null-terminated string)
+print_string:
+    pusha
+    mov ah, 0x0E
+.loop:
+    lodsb
+    test al, al
+    jz .done
+    int 0x10
+    jmp .loop
+.done:
+    popa
+    ret
+
+; Data
+BOOT_DRIVE   db 0
+MSG_BOOT     db "SUB-OS Bootloader...", 13, 10, 0
+MSG_DISK_ERR db "Boot Disk Error!", 13, 10, 0
+
+; Disk Address Packet for LBA
+align 4
+dap:
+    db 0x10         ; DAP size (16 bytes)
+    db 0            ; Reserved
+    dw 15           ; Read 15 sectors
+    dw 0x7E00       ; Offset
+    dw 0x0000       ; Segment
+    dq 1            ; Starting LBA (Sector 1)
+
+; Boot Sector Signature
+times 510 - ($ - $$) db 0
+dw 0xAA55