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AR# 56453

Is PERSIST required for Tandem Configuration solutions?


Is PERSIST of the dual purpose configuration pins required for Tandem PROM or Tandem PCIe?


Configuration Persist is required in Tandem PROM configuration. Dual purpose I/O used for first and second stage configuration cannot be re-purposed as user I/O after second stage configuration is complete. 

If you attempt to reuse these dual purpose configuration I/Os or use the STARTUPE2/E3 primitive you will see an error similar to the following:

ERROR: [DRC 23-20] Rule violation (REQP-1881) Tandem_design_fails_with_flash_programming - The STARTUPE3 cell pcie_top_1/pcie_tandem_true_gen.pcie3_ultrascale_0_1/U0/startup_i has at least one ACTIVE input pin [ DO[3:0], DTS[3:0], FCSBO, FCSBTS, USRCCLKO, USRCCLKTS, USRDONEO, USRDONETS ] and/or output pin [ DI[3:0] ] which is not compatible with use of the Tandem PROM configuration mode. To resolve this issue tie all the listed input pins of the STARTUP primitive to constant values and leave the listed output pins unconnected.

Do not remove the BITSTREAM.CONFIG.PERSIST from the constraints set, but do ensure it is set to the appropriate configuration mode (for example, BPI16). 

If the programming flash device must be updated after initial programming, external connections (not via the FPGA) are required.

Configuration Persist is not required for Tandem PCIe, as the second stage bitstream is loaded over the PCIe link.

To use Tandem PCIe in UltraScale, enable the following two options to turn off PERSIST and write two separate stage1 and stage 2 bitstreams.

set_property HD.OVERRIDE_PERSIST FALSE [current_design] 
set_property HD.TANDEM_BITSTREAMS Separate [current_design] 

Note: The above properties are for UltraScale devices only.

More information can be found in PG054, PG023, and PG156.

AR# 56453
Date 11/19/2015
Status Active
Type General Article
  • Vivado Design Suite - 2013.2
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