Add attempt for drive table to kernel

kernel/drive.asm

@@ -0,0 +1,50 @@
+%define drive_struct_len 0x0C
+
+drive_table:
+  dw 0
+.count:
+  dw 4
+
+; Drive table
+; 00  BYTE     DL number
+; 01  BYTE     file system type
+; 02  BYTE     CHS heads (ignored if LBA)
+; 03  BYTE     CHS sectors per track (ignored if LBA)
+; 04  DWORD    total number of sectors
+; 08  DWORD    partition offset
+
+; DI is incremented for the space taken
+; IN	ES:DI
+drive_setup:
+  xor cx, cx
+  mov [drive_table], di
+  mov al, drive_struct_len
+  mov ah, BYTE [drive_table.count]
+  mul ah
+  xchg cx, ax
+  ; this increments DI and also fills table with zeros
+  rep stosb
+  ret
+
+; Load a drive table entry
+; IN    DL      drive number
+; OUT   DS:SI   ptr to table item
+drive_load:
+  ; bail out if number too high
+  cmp dl, [cs:drive_table.count]
+  jnc .err
+
+  push cs
+  pop ds
+  mov si, [drive_table]
+
+  push ax
+  mov al, drive_struct_len
+  mul dl
+  add si, ax
+  pop ax
+
+  ret
+.err:
+  stc
+  ret

kernel/main.asm

@@ -31,28 +31,30 @@ isr_error:
 isr_return:
   iret
 
+%include "drive.asm"
+
 init:
   mov ax, cs
   mov ds, ax
   mov es, ax
 
+  mov di, kernel_end
+  call drive_setup
+
   mov dx, isr_dos_main
   mov ax, 0x2521
   pushf
   push cs
   call isr_dos_main
 
-  mov cx, WORD [0x80]
+  mov dl, 0x37
-  xor ch, ch
+  mov ah, 0x02
-  mov si, 0x81
+  int 0x21
-.loop:
-  lodsb
-  call putc
-  loop .loop
 
   cli
 .halt:
   hlt
   jmp .halt
 
+
 kernel_end: