Changeset 597 in xtideuniversalbios for trunk/XTIDE_Universal_BIOS/Src

Timestamp:

Jul 11, 2018, 9:44:43 AM (6 years ago)

Author:

Tomi Tilli

Message:

Windows 95 CMOS hack now works with Award BIOSes.
Some small optimizations to INT 19h and INT 19h reset handlers.
Added menuitem to configurator for clearing BDA drive count.

Location:

trunk/XTIDE_Universal_BIOS/Src

Files:

• Handlers/Int19h.asm (modified) (3 diffs)
• Handlers/Int19h/BootSector.asm (modified) (1 diff)
• Handlers/Int19h/Int19hReset.asm (modified) (1 diff)
• Initialization/DetectDrives.asm (modified) (1 diff)

trunk/XTIDE_Universal_BIOS/Src/Handlers/Int19h.asm

@@ -199 +199 @@
     call    DriveXlate_Reset                    ; Clean up any drive mappings before Rom Boot
 %endif
-    clc
-    ;; fall through to Int19h_JumpToBootSectorOrRomBoot
-
-;--------------------------------------------------------------------
-; Int19h_JumpToBootSectorOrRomBoot
+    stc
+    ;; fall through to Int19h_JumpToBootSectorInESBXOrRomBoot
+
+;--------------------------------------------------------------------
+; Int19h_JumpToBootSectorInESBXOrRomBoot
 ;
 ; Switches back to the POST stack, clears the DS and ES registers,
@@ -211 +211 @@
 ;   Parameters:
 ;       DL:     Drive to boot from (translated, 00h or 80h)
-;       CF:     Set for Boot Sector Boot
-;               Clear for ROM Boot
-;       ES:BX:  (if CF set) Ptr to boot sector (ES = zero)
+;       CF:     Clear for Boot Sector Boot
+;               Set for ROM Boot
+;       ES:BX:  (if CF clear) Ptr to boot sector (ES = zero)
 ;
 ;   Returns:
 ;       Never returns
 ;--------------------------------------------------------------------
-Int19h_JumpToBootSectorOrRomBoot:
-    mov     ax, es      ; Preserve MBR segment (can't push because of stack change)
-                        ; NOTE: can't use XOR (LOAD_BDA_SEGMENT_TO) as it impacts CF
+Int19h_JumpToBootSectorInESBXOrRomBoot:
+    mov     ax, es      ; Clear AX. NOTE: can't use XOR (LOAD_BDA_SEGMENT_TO) as it impacts CF
     SWITCH_BACK_TO_POST_STACK
 
 ; clear segment registers before boot sector or rom call
+Int19h_JumpToBootSectorInESBXOrRomBootWithoutStackChange:
+    mov     ax, es      ; Clear AX and preserve CF
     mov     ds, ax
 %ifdef USE_386
@@ -229 +230 @@
     mov     gs, ax
 %endif
-    jnc     SHORT .RomBoot
+    jc      SHORT .RomBoot
 
 ; jump to boot sector
-    push    ax          ; sgment address for MBR
+    push    es          ; sgment address for MBR
     push    bx          ; offset address for MBR
     retf                ; NOTE: DL is set to the drive number

trunk/XTIDE_Universal_BIOS/Src/Handlers/Int19h/BootSector.asm

@@ -59 +59 @@
     jne     SHORT .FirstHardDiskSectorNotBootable
 .AlwaysBootFromFloppyDriveForBooterGames:
-    stc     ; Boot Sector loaded successfully
-    jmp     SHORT Int19h_JumpToBootSectorOrRomBoot
+    clc     ; Boot Sector loaded successfully
+    jmp     SHORT Int19h_JumpToBootSectorInESBXOrRomBoot
 
 .FirstHardDiskSectorNotBootable:

trunk/XTIDE_Universal_BIOS/Src/Handlers/Int19h/Int19hReset.asm

@@ -38 +38 @@
     call    BootSector_LoadFirstSectorFromDriveDL
     jc      SHORT .Reboot
-
-    xor     ax, ax
-    mov     ds, ax
-%ifdef USE_386
-    mov     fs, ax
-    mov     gs, ax
-%endif
     cmp     WORD [bx+510], 0AA55h   ; Valid boot sector?
-    jne     SHORT .Reboot
-    push    es                      ; Zero
-    push    bx
-    retf
+    je      SHORT Int19h_JumpToBootSectorInESBXOrRomBootWithoutStackChange
 
     ; Do warm reset since boot from floppy drive failed

trunk/XTIDE_Universal_BIOS/Src/Initialization/DetectDrives.asm

@@ -118 +118 @@
         jnz     SHORT .ClearBdaDriveCount       ; Unsupported BIOS, use plan B
 
-        ; Now we can alter CMOS location 12h
+        ; Now we can alter CMOS location 12h. Important! We set type for drive 1
+        ; (primary slave) and not for drive 0! Award BIOS locks if we set drive 0 type to Fh.
+        ; We cannot set it to less either since that will fully set predefined hard drive type to the BIOS.
+        ; Windows 95 only cares that the CMOS location 12h is non-zero.
         mov     dl, HARD_DISK_TYPES
-        mov     al, 0F0h    ; Drive 0 type 16...47 but Windows doesn't care as long as this is not zero
+        mov     al, 0Fh ; Drive 1 type 16...47 (defined elsewhere in the CMOS)
         call    CMOS_WriteALtoIndexInDL
         call    CMOS_StoreNewChecksumFor10hto2Dh