Changeset 285 in xtideuniversalbios for trunk/XTIDE_Universal_BIOS/Src/Handlers/Int13h/AH15h_HSize.asm

Timestamp:

Feb 29, 2012, 7:20:36 PM (13 years ago)

Author:

aitotat@…

google:author:

aitotat@gmail.com

Message:

Changes to XTIDE Universal BIOS:

• Some minor optimizations.
• Boot menu now displays JR-IDE/ISA bus type (M8).
• Drive detection now displays ROM segment as JR-IDE/ISA Device address.

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
-
-    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
-        
+    mov     al, bh      ; AL = Max head number
+    inc     cx          ; Max cylinder number to cylinder count
+    inc     ax          ; Max head number to head count (AH=8h returns max 254 so no overflow to AH)
+    mul     bl          ; AX = Head count * Sectors per track
+    mul     cx          ; DX:AX = Total sector count for AH=0xh transfer functions
+    xor     bx, bx
     ret