• Ntdebugging Blog

    Critical Device Database TIP


    On a fairly regular basis, Bob Golding, our resident GES storage guru, sends out debugging tips to our group. We thought our blog readers would find value in these tips so we’re posting one here. Let us know what you think of the nugget.




    Hi everyone, Bob here.  Today I thought we’d have a little discussion about the Critical Device Database (CDDB) in the registry and an issue that can be caused when a device is not contained there.  This database stores configuration data for new devices that must be installed and started before the Windows components that normally install devices have been started.  The idea behind the critical device database is to allow the installation of devices without using user mode plug-and-play manager.   If a device is determined to be new, this database is queried to see if the information needed to install it are present. 

    What was the issue?

    A customer was getting a Stop 0x7B (Inaccessible_Boot_Device) after they installed a BIOS update.  Further investigation via the debugger using the !devnode command showed the following issue with a few devices:

             DevNode 0x8631f008 for PDO 0x8631f8e0

               InstancePath is "PCI\VEN_15B3&DEV_5A44&SUBSYS_5A4415B3&REV_A1\6&38f4f1f2&0&00080310"

               State = DeviceNodeInitialized (0x302)

               Previous State = DeviceNodeUninitialized (0x301)

               Problem = CM_PROB_NOT_CONFIGURED

    The above device is a bridge, and according to the definition of CM_PROB_NOT_CONFIGURED, it does not have a ConfigFlags registry entry.  I saw that this same problem occurred with a few bridges.  If the bridge cannot be enumerated, devices on the bridge will not be discovered either.  The Instance ID is used to look up the particulars such as driver name and class in the HKLM\System\CurrentControlSet\ENUM key in the registry.  What happened here is the lookup failed and the system thought it was a new device.  Since based on the device class this device was needed for boot, a Stop 0x7B occurred.

    What caused the issue?

    When the BIOS was updated the Instance ID included the version number of the bridge.  The update increased the version number, so the Instance ID was changed.

           DevNode 0x8635ca40 for PDO 0x8634c4a8

              InstancePath is "PCI\VEN_8086&DEV_1A38&SUBSYS_02DD1014&REV_B1\3&11583659&0&40"

              State = DeviceNodeInitialized (0x302)

              Previous State = DeviceNodeUninitialized (0x301)

              Problem = CM_PROB_NOT_CONFIGURED

    Looking at the registry data we could see:


    So a revision change caused the issue.

    What stops this from happening?

    Certain devices in the system are required for boot.  The device class determines if the device is in the boot device family.  If so, the hardware ID is written to the CDDB in the registry, so that if the device is determined to be new, it can be found there during boot.

    Below is an example of a bridge entry.  The contents of the pci#ven_8086&dev_244e contain the driver and the class.  This is enough to get the device started for boot.  The user mode PNP manager will complete the installation.


    How come this bridge was not there?

    When the INF was run, the device class was set to “unknown” class, so the OS did not know to write the information in the CDDB.  

    What was done to correct the problem?

    The BIOS update was temporarily reverted, and then the correct install package was found with the correct INF that has the bridges defined as a system device.  The device was re-installed (pre-update) so the device could be written properly in the CDDB, then the BIOS update was reapplied without a problem.



  • Ntdebugging Blog

    Video: Using XPERF to root cause CPU consumption


    Hi Debuggers,


    Here is a short video showing how to root cause CPU consumption issues on Vista/Server 2008 and higher operating systems with Xperf.


    For this scenario, Xperf is an easy to implement and powerful replacement for previous actions like gathering a series of dumps during the CPU, kernrate data, perfmon, other profilers, etc.


    Xperf allows one to quickly turn on profiling and see where the CPU time is being spent by using tracing already in the box!






    Note - Feel free to post questions here, or jump into a discussion about the video on our Twitter page ( @ntdebugging ).



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  • Ntdebugging Blog

    We Need Your XPERF Feedback




    This is Tate asking for your direct and valuable feedback on XPerf (The Windows Performance Toolkit).  We are knee deep in working with the creators of the tool (The Windows Fundamentals Team) to provide end user feedback which will drive features for the next version. Now that you as our readers have seen several blog posts on the utility and hopefully have used it for a few of your own debugs, what would you like to see in terms of new features, fixes, data collection steps, etc?


    Particular areas of interest to the team are:


    -        Data Collection – easy or difficult, what would you change?

    -        Usage Scenarios – stack walking is powerful, what would you like the tool to expose that it does not?

    -        Any blocking factors keeping you from using the toolkit, what are they, how could we remedy that for you?

    -        Data Analysis – what would make your life as a debugger using the toolkit better?


    Please send us your feedback below and thanks in advance.



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