AR# 60131
Vivado Placer - [Place 30-378] Input pin of input buffer has an illegal connection to a logic constant value
Description
I am adding old NGC files as sources to my Vivado project.
I am receiving the following errors when trying to place the design:
[Place 30-378] Input pin of input buffer hierarchy_path_to_cell/clk_BUFGP/IBUF has an illegal connection to a logic constant value.
[Place 30-378] Input pin of input buffer hierarchy_path_to_cell/clk_BUFGP/IBUF has an illegal connection to a logic constant value.
[Place 30-378] Input pin of input buffer hierarchy_path_to_cell/clk_BUFGP/IBUF has an illegal connection to a logic constant value.
[Place 30-378] Input pin of input buffer hierarchy_path_to_cell/CH0_CLK_BUFGP/IBUF has an illegal connection to a logic constant value.
[Place 30-99] Placer failed with error: 'Implementation Feasibility check failed, Please see the previously displayed individual error or warning messages for more details.
'Please review all ERROR, CRITICAL WARNING, and WARNING messages during placement to understand the cause for failure.
What is wrong here and how can I fix this?
Solution
These errors are pointing to BUFGP primitives in the NGC files being used.
BUFGP primitives must connect to a port.
When you view the Synthesized netlist in Vivado, it can be seen that the BUFGP primitive is transformed to an "IBUF -> BUFG", see schematic shot below.
The BUFG -> IBUF -> BUFG path causes the errors reported.
Recommended Solution:
Ensure that the NGC files are created with the "-iobuf" switch set to false for XST.
This will result in this construct not being produced and if the original projects exist it is a very straight forward way to avoid this error.