    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.