I have imported my working ISE project from the revision control repository, on opening the PlanAhead project, all sources are present and can be viewed in the hierarchy of the design source pane within the PlanAhead GUI.
However, when I synthesize the design I get an error after the first IP core has been generated stating that the XCO source for the other IP cannot be found, and in the hierarchy of the design source pane in the GUI, these XCO files now show a question mark and are no longer correctly referenced in the design.
Why is this the case?
Upon further investigation, it was noticed that ISE Project Navigator will place all IP cores and their output files, including XCO files, into one "ip_cores" directory. This works well for ISE Project Navigator. However, when this project is imported into the PlanAhead tool, then this directory structure remains for the PlanAhead project; that is, all IP are placed in an "ip_cores" directory. The PlanAhead tool does not work this way normally and would usually create a directory for each IP added, for instance, "ip_cores/addsub" and "ip_cores/multiplier" etc.
This allows the PlanAhead tool on regeneration to purge the output location of all files. In this specific case where all IP XCO files are in this single "ip_cores" directory, all XCOs are deleted and as such only the first IP core in the list will be regenerated and the others will not be found.
To work around this issue, it is necessary to manually add each IP core to the PlanAhead project, thus creating individual source directories which will avoid the loss of IP sources on regeneration.
Please note that this will not be an issue with the Vivado 2013.1 or PlanAhead 14.5 tools, as the purge of this directory has been removed to avoid this situation and other issues where files not owned by the Xilinx software were getting removed incorrectly as well, for instance, revision control files and directories.