Tandem PROM configurations do not allow the dual purpose configuration I/O to be
used for stage 1 or stage 2 configurations. This prevents access to the external
configuration flash for Tandem PROM designs. Because of this, the configuration flash
cannot be accessed by the user design after Tandem PROM configuration completes. Tandem
PCIe should be used if configuration flash update
from the FPGA user design is required. Configuration Persist is set automatically during
write_bitstream, and is set in such a way that the
ICAP (which must remain out of stage 1) is functional in the user design.
If the CONFIG_MODE option is set correctly for the needed configuration mode, but
necessary dual-mode I/O pins are still occupied by user I/O, the following error is
issued for each instance during write_bitstream:
ERROR: [Designutils 12-1767] Cannot add persist programming for site IOB_X0Y151.
ERROR: [Designutils 12-1767] Cannot add persist programming for site IOB_X0Y152.The user I/O occupying these sites must be relocated to use Tandem PROM.