From 554ada6fc34d8b1f43c062ddce6f6f12c2cde1d7 Mon Sep 17 00:00:00 2001
From: heckeralt <hecker@kevinthe.horse>
Date: Sat, 5 Oct 2024 12:46:22 -0400
Subject: [PATCH] Add boot.asm

---
 boot.asm | 120 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 boot.asm

diff --git a/boot.asm b/boot.asm
new file mode 100644
index 0000000..d1f6c89
--- /dev/null
+++ b/boot.asm
@@ -0,0 +1,120 @@
+[bits 16]               ; Set to 16-bit mode
+[org 0x7C00]           ; BIOS loads the bootloader at this address
+
+; Define GDT
+gdt_start:
+    dw 0x0000          ; Limit (low)
+    dw 0x0000          ; Base (low)
+    db 0x00            ; Base (mid)
+    db 0x9A            ; Access byte: Present, ring 0, executable
+    db 0xCF            ; Flags: Granularity, 32-bit
+    db 0x00            ; Base (high)
+
+    dw 0x0000          ; Limit (low)
+    dw 0x0000          ; Base (low)
+    db 0x00            ; Base (mid)
+    db 0x92            ; Access byte: Present, ring 0, writable
+    db 0xCF            ; Flags: Granularity, 32-bit
+    db 0x00            ; Base (high)
+
+gdt_descriptor:
+    dw gdt_end - gdt_start - 1   ; Limit
+    dd gdt_start                   ; Base address
+
+gdt_end:
+
+start:
+    cli                     ; Disable interrupts
+    lgdt [gdt_descriptor]   ; Load GDT
+    mov eax, cr0           ; Read CR0 register
+    or eax, 1              ; Set PE bit (Protected Mode Enable)
+    mov cr0, eax           ; Write back to CR0
+
+    jmp 0x08:protected_mode_entry ; Far jump to flush the pipeline
+
+protected_mode_entry:
+    mov ax, 0              ; Set data segment to the new segment
+    mov ds, ax             ; Load data segment register
+    mov es, ax             ; Load extra segment register
+    mov fs, ax             ; Load fs segment register
+    mov gs, ax             ; Load gs segment register
+
+    call clear_screen      ; Clear the screen
+    mov si, welcome_message 
+    call print_string_protected
+    
+command_loop:
+    mov si, prompt_message
+    call print_string_protected
+
+    call read_input
+
+    cmp al, 'h'      ; Check for 'h' command (help)
+    je print_help
+    cmp al, 'q'      ; Check for 'q' command (quit)
+    je quit_terminal
+    cmp al, 'f'      ; Check for 'f' command (heckerfetch)
+    je heckerfetch
+    
+    mov si, unknown_command_message
+    call print_string_protected
+    jmp command_loop  ; Repeat the command loop
+
+print_help:
+    mov si, help_message
+    call print_string_protected
+    jmp command_loop  ; Return to command loop
+
+heckerfetch:
+    mov si, heckerfetch_message
+    call print_string_protected
+    jmp command_loop  ; Return to command loop
+
+quit_terminal:
+    mov si, goodbye_message
+    call print_string_protected
+    jmp hang          ; Hang the system
+
+; Function to read a character from keyboard input
+read_input:
+    xor eax, eax       ; Clear EAX for reading character input
+    int 0x16          ; Call BIOS interrupt to read a character into AL
+    ret                ; Return with character in AL
+
+; Function to print a string in protected mode using VGA text buffer
+print_string_protected:
+    mov edi, 0xb8000     ; VGA text buffer address
+.next_char:
+    lodsb                ; Load byte at DS:SI into AL and increment SI
+    cmp al, 0           ; Check for null terminator
+    je .done            ; If null, we are done
+    mov [edi], ax       ; Write character and attribute (white on black)
+    add edi, 2          ; Move to next character cell
+    jmp .next_char      ; Repeat for next character
+.done:
+    ret                  ; Return from function
+
+; Function to clear the screen in protected mode
+clear_screen:
+   xor di, di           ; Start from the beginning of the VGA buffer 
+   mov cx, 80 * 25      ; Number of characters in a standard text mode screen 
+   mov ax, 0x07        ; Attribute for white on black background 
+.fill_screen:
+   stosw                ; Store word in [ES:DI] and increment DI by 2 
+   loop .fill_screen     ; Repeat until CX is zero 
+   ret                  ; Return from function
+
+; Data section for messages 
+welcome_message db 'Welcome to the HeckerOS!', 0 
+prompt_message db 'Enter command (h for help, q to quit, f for heckerfetch): ', 0 
+help_message db 'Available commands: h (help), q (quit), f (heckerfetch)', 0 
+unknown_command_message db 'Unknown command! Try again.', 0 
+goodbye_message db 'Goodbye!', 0 
+heckerfetch_message db 'OS: HeckerOS Beta, CPU: HeckerSoft Generic CPU 0GHZ', 'Host: HeckerSoft Unknown Host', 0 
+
+; Bootloader signature (must be present) 
+times 510 - ($ - $$) db 0   ; Fill the rest of the sector with zeros 
+dw 0xAA55                   ; Boot signature 
+
+hang:
+   jmp hang           ; Jump to hang indefinitely 
\ No newline at end of file