Common problems

This page contains a list of issues encountered using ISE 9.2 on the PCs in BE104 and how to work around them. Some of these are ISE quirks and some of these are common human failings.

General Problems

ISE 9.2 does not crash very often. Things that tend to make it and Windows more likely to crash are:

• running other large processes, e.g iTunes and multiple browser windows
• running a long time. After 4-5 hours it is worth your while to close ISE, logout from the PC and move to another PC.

Always make sure to wait for the logout to complete before logging in to another PC. After finding your current files intact on the new PC, you can reboot the first PC. If your files are not there, DO NOT LOGIN TO THE FIRST PC. Doing so will erase the only remaining copy of your most recent files. Find someone who has administrative rights on the BE104 PCs to help you. They can login to the first PC and copy your files to a safe place so that you can access them. But if you login before your files are copied to a safe location, then your current files will be overwritten with an older version!!!

If you discover that you are logged into two PCs, logout last from the PC with the files you want saved.

Known Quircks, Common Errors, and their Solutions

1. ISE Project Navigator can't open my project when I start it by double clicking on my project. This seems to be an issue related to the user permissions on the BE104 PCs.

Solution: Simply open the Project Navigator by double clicking on the icon on the desktop and then open your project by selecting "Open Project" in the File menu.

2. In the schematic there is a wire I can't find which DRC flags as an error so I can't compile my design. You have created a wire of zero length. It has a spiritual, but not physical presence and hence cannot be selected for deletion.

Solution: Write out your schematic file and close the schematic window. Then re-open this schematic and the spirit of the wire should be gone. Aparently this problem is detected and fixed when the file is either written or read. If that fails you can always use WordPad on the schematic file (save a copy first!) to try to fix the problem. Your schematic named "Foo" will be in the file "Foo.sch".

3. ISE crashed and now it can't read my schematic back in. This has been known to happen when ISE (or more appropriately Windows) crashes while writing your file. There is an excellent chance you can recover all or a large part of your schematic.

Solution: Look for the file "Foo.sch" in your project directory where "Foo" is the name of your schematic. Make a copy of this file and then use WordPad to take a look at "Foo.sch". This is an ASCII file with a list of the symbols and wires in your schematic. Look at the end of the file to see what's missing. Often it's just "END" statements matching the "BEGIN" statements near the start. You can recover what's in the file by merely adding the appropriate "END" statements. You may need to study the structure of the file.

4. My symbol is strange and ISE won't change it. Did you run DRC before trying to make the symbol?

Solution: Sometimes the only way to get ISE to remake a symbol is by forcing the issue. For the schematic and symbol named "Foo" remove the file "Foo.sym" from the project directory (not "Foo.sch"!!!). ISE will then have no choice but to make the symbol from scratch. But please run DRC on your schematic before making the symbol. Make sure you are in the correct project directory!!

5. My new symbols aren't showing up in the Symbol Library in the schematic window. This happens sometimes when you un-dock the schematic from the Project Navigator. It seems to be a window communication problem.

Solution: Re-dock your schematic window and then the symbols should appear. You can them undock it again.

6. The ISE simulator is acting strange. The previous simulator process was not shutdown and is still active.

Solution: Use the Windows Task Manager to find the process and terminate it.

7. The MAP process complains about multiple IBUFs/OBUFs at a location. LOC attributes should be attached only to IBUFs and OBUFs.

Solution: Check that you haven't added the LOC attributes to the I/O markers. They won't be visible in the schematic; you need to select them and look at their Object Properties to see their attributes. It's also possible that you have used the same location twice; this can easily happen when you copy and paste the IBUFs/OBUFs and forget to change their attributes.

8. The SYNTHESIS process (or DRC) reports that there are multiple sources for a wire. This means you have two or more outputs connected to the same wire. This happens when a wire becomes disconnected and its pieces are reused. The wire names are not visible and so you don't realize that the pieces still have the same name.

Solution: Look at the error report to find the offending symbols and then look at the wires connected to their outputs. If you slide the cursor over a symbol it should tell you the names of the wires connected to its pins. Just fix it!

9. Some of the LEDs I'm not using are turning on. You have I/O markers in your top level schematic which are not coming from IBUFs or OBUFs or you didn't set their LOC attributes correctly. Unplug the power to the board NOW; you may be driving an input.

Solution: Under the Place&Route process you should find the pad report which shows the FPGA pads/pins used by your design and the names of the signals connected to them. Check that these are correct. If you have added IO markers to signals in your top level that aren't inputs or outputs remove those markers. You should not have added them. See the ISE Simulation Tutorial to find out how to get these signals into your Waveform Viewer without adding IO markers to the schematic.

10. The Project Navigator is complaining it can find some of the Xilinx symbols in my schematic. The project properties are probably not correct.

Solution: Under the Source menu selected Project Properties. Make sure they are set correctly as shown in the tutorial on Creating a New Project.

The CMPE100 Web: Copyright 2011; Department of Computer Engineering, University of California, Santa Cruz.