In some cases where the VHDL entity and architecture are defined in separate files, the following warning can be observed after running Vivado Synthesis:
WARNING: [Synth 8-1824] circular dependency found for file <name>.vhd while ordering
These warnings can be ignored.
However, after some of these warnings the following error can be seen:
ERROR: [Synth 8-1940] entity ... is not yet compiled
Here are few options to get around this problem:
1. Merge the VHDL entity and architecture into one VHDL file.
2. a) Select the No Update, Manual Compile Order in the Hierarchy Update Tab either in the Hierarchy field or Compile Order field.
b) Move the Architecture file before the Entity file for those files Vivado Synthesis generated the [Synth 8-1940] error message.
c) Run Vivado Synthesis, that should allow synthesis to run successfully.
3. If there is only a warning and the design finishes without an Error message, the user should be able to move on with the next step.
A fix is planned for Vivado 2012.4