Subject: Space Quest IV SoundBlaster Fix                                        
                                                                                
Intro                                                                           
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On OS/2 2.0 304E, Space Quest IV experiences problems in a DOS session.         
On machines that have the SoundBlaster card, it runs for about 30               
seconds, and then stops.  The problem was found to be related to DMA            
transfers and simulated interrupts.                                             
                                                                                
Fix Description                                                                 
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After debugging for several days, a fix was found for the SNDBLAST.DRV          
file that comes with Space Quest IV.  This fix makes the interrupt handler      
for the SoundBlaster card work better under a Virtual 86 environment.           
Essentially, it guarantees that the SoundBlaster card is in the correct         
state before it sends an End of Interrupt (EOI) to the Programmable Interrupt   
Controller. We have patched the SNDBLAST.DRV file and it now works correctly.   
Essentially, the EOI is at the end of the interrupt handler instead             
of at the beginning.                                                            
                                                                                
Why Not Change OS/2?                                                            
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Changing OS/2 for this problem would mean a great deal of work.  Interrupt      
simulation would have to change so that it would be impossible to ever          
enable interrupts while running a DOS interrupt handler.  All associated        
code would have to be resident (present), and the DOS address space for         
interrupt handlers could never cross a page-boundry without the pages           
being present.  This is not a trivial fix. The fix was to move four             
bytes of code in the SNDBLAST.DRV instead of trying a major change to           
OS/2.                                                                           
                                                                                
Sierra Contact                                                                  
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Sierra was contacted to discuss the change.They agreed that it was a            
good change and that it might partially explain why Space Quest IV              
doesn't work under Windows Enhanced Mode Dos sessions. We expect that           
they will incorporate this idea into their products from this day on.           
                                                                                
Patch for Customers                                                             
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We have built a executable called SQ4FIX.COM that runs in a DOS session.        
We are putting this file into the product, and it will be installed             
into \OS2\MDOS when the user selects the DOS & Win-OS/2 section during          
install.  To use this patch program, the user only has to change to the         
drive which has Space Quest IV installed and execute the program.               
                                                                                
Example:                                                                        
                                                                                
D:\> sq4fix                                                                     
                                                                                
There are no parameters to worry about and SQ4FIX will do error checking.       
The README for GA is being updated to inform the user about this                
program and how to use it.