Changeset 78 for trunk/bootcode/regular/other.asm

Timestamp:

Apr 8, 2017, 12:26:16 AM (8 years ago)

Author:

Ben Rietbroek

Message:

More hard-coded '80h' corrections [v1.1.1-testing]

Code in 'partmain.asm' around line 1350 needs some more attention.
Possibly the whole 'boot-flag' stuff is not needed with modern BIOSses.
Updating them is disabled for now, which should only affect very old
BIOSses that don't leave this checking to the MBR code.

CAUTION:
This is a testbuild !
AirBoot uses the BIOS to access disks and a small coding error can trash
partition tables or other vital disk structures. You are advised to make
backups of TRACK0 and EBRs before using this testbuild. More info at:
​https://rousseaux.github.io/netlabs.air-boot/pdf/AirBoot-v1.1.0-manual.pdf

File:

• trunk/bootcode/regular/other.asm (modified) (2 diffs)

trunk/bootcode/regular/other.asm

@@ -166 +166 @@
         call    MBR_TeletypeNL
 
+        ;
+        ; Write MBR back to disk to sync MBR variables.
+        ; Otherwise subsequent MBR loads will differ from the RAM stored one,
+        ; which is used by MBR protection to validate parts of the MBR.
+        ;
+        xor     bx, bx
+        mov     cx, 1
+        xor     dh, dh
+        mov     dl, [BIOS_BootDisk]
+        mov     al, 1
+        mov     ah, 03h
+        int     13h
+
+
+        ; Start with disk at index 0
         xor     cx,cx
+
     PRECRAP_Main_next_disk:
 
+        ; Get next disk and convert to BIOS disk-number
         mov     dl,cl
         or      dl,80h
@@ -431 +448 @@
         mov     ah, 41h
         mov     bx, 55AAh
-        mov     dl, 80h
+        mov     dl, [BIOS_BootDisk]     ; We check using the boot-disk
         int     13h
         cmp     bx, 0AA55h