Changeset 542 in xtideuniversalbios for trunk/XTIDE_Universal_BIOS/Src/Handlers/Int13h/EBIOS/AH48h_GetExtendedDriveParameters.asm

Timestamp:

Apr 15, 2013, 4:03:33 PM (11 years ago)

Author:

aitotat@…

google:author:

aitotat@gmail.com

Message:

Changes to XTIDE Universal BIOS:

• Fixed a bug that allowed EBIOS functions for user defined CHS.
• Simplified user defined CHS and LBA setup a little.

File:

• trunk/XTIDE_Universal_BIOS/Src/Handlers/Int13h/EBIOS/AH48h_GetExtendedDriveParameters.asm (modified) (2 diffs)

trunk/XTIDE_Universal_BIOS/Src/Handlers/Int13h/EBIOS/AH48h_GetExtendedDriveParameters.asm

@@ -52 +52 @@
 ;    AH=48h Total Sector Count: 11873* 16*63 = 11,967,984
 ;
-; Notice how AH=48h returns lesser total sector count than AH=8h! The only
+; Notice how AH=48h returns lesser total sector count than AH=08h! The only
 ; way I could think of to get 11873 cylinders is to divide AH=08h sector
 ; count with P-CHS heads and sectors: (745*255*63) / (16*63) = 11873
 ;
-; I have no idea what is the reasoning behind it but at least there is one
-; BIOS that does just that.
-;
-; I decided that we multiply P-CHS values and do not waste space like the
-; Award BIOS does.
+; The only reason I can think of is that the Award BIOS has a bug and
+; uses L-CHS when it should use P-CHS values in the calculation.
 ;
 ;
@@ -139 +136 @@
     ; Store P-CHS. Based on phoenix specification this is returned only if
     ; total sector count is 15,482,880 or less.
-    sub     ax, 4001h
-    sbb     dx, 0ECh
+    sub     ax, MAX_SECTOR_COUNT_TO_RETURN_PCHS & 0FFFFh
+    sbb     dx, MAX_SECTOR_COUNT_TO_RETURN_PCHS >> 16
     sbb     bx, cx      ; Zero
-    jnc     SHORT .ReturnWithSuccess    ; More than EC4000h
-    or      WORD [di+EDRIVE_INFO.wFlags], FLG_CHS_INFORMATION_IS_VALID
+    ja      SHORT .ReturnWithSuccess
+    or      BYTE [di+EDRIVE_INFO.wFlags], FLG_CHS_INFORMATION_IS_VALID
 
     eMOVZX  dx, BYTE [es:si+DPT.bPchsHeads]