Byte Merging

["Robert Hormuth" <Robert.Hormuth@natinst.com>]

     We have recently found a few computers that turn BYTE MERGING on in 
     the chip set even when there are PCI cards in the system that indicate

     they are not prefetchable.  Has anyone else seen this problem or other

     problems from byte merging?  What have you done for work arounds?  We 
     are seeing bytes being merged on incrementing and decrementing 
     addresses(BYTES), this seems highly dangerous to IO and Memory Mapped 
     cards.  Thus if the CPU writes bytes to address 3,2,1,0 it comes out 
     at address 0 with all byte enables asserted, likewise when it writes 
     to 0,1,2,3 it does the same thing.  As a plug in card you don't know 
     which write to do first to your actual device, thus the instruction 
     order is broken.
     
     
     Thanks,
     
     Robert Hormuth
     Staff Design Engineer
     National Instruments
     6504 Bridge Point Parkway
     Austin, Texas 78730
     roberth@natinst.com
     (512) 433 - 8630 Phone
     (512) 433 - 8641 Fax

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