AST RESEARCH, INC.         TECHNICAL BULLETIN #1307               9-6-95


              PCICHK AND I/O OVERLAP CONFLICTS  WITH CMD CHIP

PROBLEM:    When a PCI board is installed in a system that incorporates 
            a CMD640 or a CMD646 EIDE (Enhanced IDE) chip, Adaptec's 
            PCICHK utility reports errors.  The error message will 
            indicate there is an I/O overlap error with the PCI add-in 
            card and the CMD chip.  A literal interpretation of the 
            error would indicate the CMD chip is grabbing more address 
            space than it is actually using.  Consider the following 
            example of the error reported:

                I/O:
                     OVERLAP conflict exists between
                     Device 0:6:0
                     which has a 3rd Base Address Register
                     with base = 00000000, limit = fff0007
                Device 0:a:0
                     which has a 1st Base Address Register
                     with base = 0000fc00, limit = 0000fcff

CAUSE:      The PCICHK utility is incorrectly reporting an overlap 
            conflict with the CMD chip due to the fact that the CMD chip 
            only implements the lower 16 bits of its BAR (Base Address 
            Register).  The algorithm used by the utility to determine 
            address space requested by a BAR does not know this and will 
            report that the third and fourth BARs are in conflict with 
            most PCI cards.

SYSTEMS AFFECTED:
            All AST systems using the CMD640 or CMD646 PCI IDE 
            controller chip.

SOLUTION:   Errors of this type that point to the CMD controller may be 
            ignored as the BARs in question are disabled therefore no 
            I/O overlap conflict can exist.

            This technical bulletin is provided for informational 
            purposes only.