I receive a "MAP fails" with the following error. Why?
"ERROR:Pack:1107 - Unable to combine the following symbols into a single DIFFS component:
PAD symbol "inst0_IOBUFDS_IOB" (Pad Signal = inst0_IOBUFDS_IOB)
SlaveBuffer symbol "inst0_IOBUFDS_IOB.DIFFIN" (Output Signal = inst0_IOBUFDS_IOB.DIFFIN)
SlaveBuffer symbol "inst0_IOBUFDS_IOB.DIFFOUT" (Output Signal = inst0_IOBUFDS_IOB)
More than one SLAVE buffer. The current IOSTANDARD does not support bidirectional usage."
This pack error occurs because an IOBUFDS is being used, but no I/O standard is assigned to it, and an unsupported I/O standard is being selected by default. (Virtex-II Pro does not support bidirectional usage for LVDS_25.)
This problem will be fixed in design tools version 8.2i. Meanwhile, you can avoid the problem by assigning valid I/O Standards to all IOBUFDS symbols in Virtex-II Pro designs.
In general, when I/O Standards are not properly defined for all I/O components, default values are chosen by MAP. Appropriate values are not always chosen which can lead to a variety of failure modes including pack errors and I/O banking rule errors.