Commented disk_mng.asm

Author: Retr0-code

boot.asm

@@ -36,10 +36,10 @@ section .text:
         pop ax                      ; Recover AX value from stack
         pop bx                      ; Recover BX value from stack
         
-        mov [disk_index], dl
-        mov bx, kernel_address
-        mov dh, 2
-        call _read_disk
+        mov [disk_index], dl        ; Save boot disk to variable
+        mov bx, kernel_address      ; Write to BX kernel origin
+        mov dh, 2                   ; Read two sectors
+        call _read_disk             ; Read 16 bits from disk
 
         jmp $                       ; Stops the processor
 
@@ -52,10 +52,10 @@ section .text:
     
         buffer: times 4 db 0        ; Defines input buffer
 
-        kernel_address: equ 0x1000
-        disk_index: db 0
+        kernel_address: equ 0x1000  ; Kernel origin
+        disk_index: db 0            ; Variable to store boot drive index
 
- Global Descriptor Table
+; Global Descriptor Table
 GDT_start:
     GDT_null:
         dd 0x0

functions/disk_mng.asm

@@ -2,23 +2,23 @@ global _read_disk
 
 section .text:
     _read_disk:
-        pusha
-        push dx
-
-        mov ah, 0x02
-        mov al, dh
-        mov cl, 0x02
-        mov ch, 0x00
-        mov dh, 0x00
-
-        int 0x13
-        jc disk_error
-
-        pop dx
-        cmp al, dh
-        jne sectors_error
-        popa
-        ret
+        pusha               ; Push registers
+        push dx             ; Save dx to the stack
+
+        mov ah, 0x02        ; Enable disk reading
+        mov al, dh          ; Amount sectors to read
+        mov cl, 0x02        ; Read from second sector
+        mov ch, 0x00        ; Cylinder to read from
+        mov dh, 0x00        ; Head that read
+
+        int 0x13            ; BIOS interupt to read data
+        jc disk_error       ; If carry is set raise an error
+
+        pop dx              ; Recover DX from stack
+        cmp al, dh          ; Check amount of readen sectors
+        jne sectors_error   ; If they are not equal raise an error
+        popa                ; Recover registers
+        ret                 ; Exit the function
 
 
     disk_error: