kernel: Only start the BIOS timer if there is an actual access to selector 0x40.

dlls/krnl386.exe16/dosexe.h

@@ -393,6 +393,7 @@ extern DOSCONF *DOSCONF_GetConfig( void );
 
 /* dosmem.c */
 extern BIOSDATA *DOSVM_BiosData( void );
+extern void DOSVM_start_bios_timer(void);
 
 /* fpu.c */
 extern void WINAPI DOSVM_Int34Handler(CONTEXT86*);

dlls/krnl386.exe16/dosmem.c

@@ -264,6 +264,19 @@ static DWORD CALLBACK timer_thread( void *arg )
 }
 
 /***********************************************************************
+ *           DOSVM_start_bios_timer
+ *
+ * Start the BIOS ticks timer when the app accesses selector 0x40.
+ */
+void DOSVM_start_bios_timer(void)
+{
+    static LONG running;
+
+    if (!InterlockedExchange( &running, 1 ))
+        CloseHandle( CreateThread( NULL, 0, timer_thread, DOSVM_BiosData(), 0, NULL ));
+}
+
+/***********************************************************************
  *           DOSMEM_Collapse
  *
  * Helper function for internal use only.
@@ -335,7 +348,6 @@ BOOL DOSMEM_InitDosMemory(void)
                   DOSMEM_Available());
 
             DOSVM_InitSegments();
-            CloseHandle( CreateThread( NULL, 0, timer_thread, DOSVM_BiosData(), 0, NULL ));
 
             SetEvent( hRunOnce );
             done = 1;

dlls/krnl386.exe16/instr.c

@@ -104,6 +104,7 @@ static BOOL INSTR_ReplaceSelector( CONTEXT86 *context, WORD *sel )
 {
     if (*sel == 0x40)
     {
+        DOSVM_start_bios_timer();
         *sel = DOSMEM_BiosDataSeg;
         return TRUE;
     }