Changeset 283 in xtideuniversalbios

Timestamp:

Feb 29, 2012, 11:42:52 AM (13 years ago)

Author:

gregli@…

google:author:

gregli@hotmail.com

Message:

Fixed bug where total sector count was not being properly calculated from ah08 values, as head value is zero based instead of one based. The calcaultion is more complicated than one would like because the head number is in a single byte and could be 255 and we need to avoid an overflow.

File:

• trunk/XTIDE_Universal_BIOS/Src/Handlers/Int13h/AH15h_HSize.asm (modified) (1 diff)

trunk/XTIDE_Universal_BIOS/Src/Handlers/Int13h/AH15h_HSize.asm

@@ -77 +77 @@
 ConvertAH08hReturnValuesToSectorCount:
     call    Address_ExtractLCHSparametersFromOldInt13hAddress
-    xchg    ax, cx
-    inc     ax              ; Max cylinder number to cylinder count
-.MultiplyChsInAXBLBHtoBXDXAX:
-    xchg    bx, ax
-    mul     ah          ; Multiply heads and sectors
-    mul     bx          ; Multiply with cylinders
-    xor     bx, bx
+
+    mov     al, bl      ; Get sector value
+    mul     bh          ; Multiply by heads-1 (since bh is zero based, and could be 255 and overflow)
+    xor     bh, bh      ; Clear upper byte for following addition...
+    add     ax, bx      ; Add in one more sector value, since heads was off by one
+    inc     cx          ; Max cylinder number to cylinder count (again, zero based)
+    mul     cx          ; Multiply in cylinders
+    xor     bx, bx      ; Zero upper 16-bits, sector count will not be that large
+        
     ret