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fwkpfv(1)                 BSD General Commands Manual                fwkpfv(1)


     fwkpfv -- FireWire kprintf viewer


     fwkpfv [--appendlog] [--openlog] [--newlog] [--prefix] [--publish]
            [--single] [--buffer=boot-args] [--setargs[=boot-args]] [--setpm]
            [--disable] [--erase] [--ioff] [--restart] [--help]


     Use fwkpfv to receive FireWire kprintf logging. FireWireKPrintf redirects
     "kprintf()" logging to FireWire. Kernel printfs or "kprintfs" are used by
     many kernel services as a low level logging mechanism. They can also be
     used in third party kernel extensions. FireWire kprintfs are available
     very early in the kernel's startup and right until the cpu is powered
     down at sleep, restarted, or shutdown. Similarly, they are available
     almost as soon as the cpu is powered when waking. They can be useful for
     debugging kernel code (including KEXTs), particularly sleep/wake issues
     where the display and/or ethernet is unavailable.


     The available options are as follows:

     --appendlog, -a
            Append output logging to /tmp/fwkpf.log.

     --openlog, -o
            Open log file with Only valid with -a.

     --newlog, -n
            Create a new log file, rather than append. Only valid with -a.

     --prefix, -p
            Prefix logger machine's ID to each log.

     --publish, -k
            Do not publish FireWire unit directory keys.

     --single, -s
            Use a single window even if multiple loggers are present.

     --buffer=size, -bsize
            Sets the host's psuedo address space queue buffer to sizein bytes.
            Increasing this value may help avoid potential packet loss. The
            default buffer size is 204,800 bytes.

     --file=path, -b-path
            Sets the log file path, if in use, to pathgiven as a path to a
            file. The tilde character is not allowed.

     --setargs[=boot-args], -r[boot-args]
            Sets the nvram boot-args on the current machine to boot-args. This
            flag should only be used on the target machine (which is contrary
            to typical usage cases, when this tool is used on the host). If
            boot-args is not passed, the tool will prompt the user as to which
            boot-args are to be set.

     --setpm, -m
            Sets the nvram boot-args on the current machine to "debug=0x14e
            io=0x880". This flag should only be used on the target machine
            (which is contrary to typical usage cases, when this tool is used
            on the host).

     --disable, -x
            Sets the nvram boot-args on the current machine to "debug=0x146"
            which disables kprintf logging. This flag should only be used on
            the target machine (which is contrary to typical usage cases, when
            this tool is used on the host).

     --erase, -e
            Deletes the boot-args variable from nvram. This flag should only
            be used on the target machine (which is contrary to typical usage
            cases, when this tool is used on the host).

            Turns off interactive mode.

            Automatically restarts the machine only after the nvram has been
            modified by this tool.

     --help, -h
            Displays usage info for fwkpfv.


     Unlike in the past, Mac OS X 10.5 has integrated FireWireKPrintf func-
     tionality, so it is not necessary to install a separate kext to enable
     kprintf logging over FireWire.

     While the symbol for kprintf() is available at all times, the calls are
     essentially ignored unless activated with a boot argument (see below).

     While the new FireWireKPrintf is integrated with the normal FireWire
     stack, once the machine begins logging kprintfs via FireWire, normal
     FireWire services will stop until the machine is restarted. Once in log-
     ging mode, all typical FireWire services (like FireWire hard disk access)
     will be unavailable. It is expected that any devices connected before
     logging will be forcefully removed.  If you need to log while also using
     the FireWire stack, please use FireLog (see the FireWireSDK).

     The new integrated FireWireKPrintf cannot be used while the old Apple-
     FireWireKPrintf.kext is installed. Remove it to use the integrated ver-

     The new viewer will be able to capture kprintf logs from the old-style
     AppleFireWireKPrintf.kext, however, the old-style viewer will not work
     with the integrated FireWireKPrintf services.


     To use the FireWireKPrintf, two machines must be setup as such:

          -   On the Target machine (to be debugged):
                    1.   Boot the Mac from the partition you wish to use.
                    2.   Set kernel boot arguments to enable kernel printfs:
                               % sudo nvram boot-args="debug=0x8"
                         While only the debug bit equivalent to '0x8' is
                         required for kprintf logging, you may want to set the
                         debug variable to '0x14e' to enable other debugging
                         services. For more information on the debug flags,
                         please see Technical Note TN2118. For more logging
                         options, please see <Kernel/IOKit/IOKitDebug.h>.
                    3.   Restart the target Mac.
                    4.   Disconnect any FireWire device.

          -   On the debugger machine with Mac OS X and Developer Tools
              installed, run from
                    % fwkpfv
                    (If the machine is running Tiger: Run the FireWireKPrintf
                    viewer tool included in the FireWireSDK available at

          -   Connect the two machines together using a FireWire cable.

          -   After 5 seconds, you should see output in the viewer and kprintf
              logging is flowing. Note: At this point, normal FireWire ser-
              vices will cease to exist on the target until the machine is


     FireWireKPrintf implements a few options that can be set as a "boot-arg,"
     much like the "debug" variable. The "fwkpf" variable specifies the time-
     stamp format (calculated on the target, before transmission), timestamp
     padding, verbose kprintf printing, and synchronous mode. To set the
     "fwkpf" variable, choose a timestamp unit and add any of the "additive"
     options. The default timestamp is 0x4 (microseconds).

     Timestamp Formats (not additive):

     0x0      Converted FW Cycle Time Units (c) - Classic time format shown as
              "Seconds.Microseconds". The Second unit rolls over every 128
              seconds. Driven by the FireWire clock.

     0x1      Absolute Time Units (a) - "Absolute" time units derived directly
              from the kernel's uptime clock.

     0x2      FireWire Time Units (w) - Shown as "Seconds:Cycles:Offset".
              Driven by the FireWire clock. Seconds rollover every 128 sec-
              onds. 8000 cycles per second. 3072 offset counts per cycle.
              Equivalent to FireBug's time format.

     0x3      Nanoseconds Time Units (n) - The kernel's uptime clock converted
              to nanoseconds.

     0x4      Microseconds Time Units (u) - The kernel's uptime clock con-
              verted to microseconds.

     0x5      Milliseconds Time Units (m) - The kernel's uptime clock con-
              verted to milliseconds.

     0x6      Seconds Time Units (s) - Shown as "Seconds:Millisec-
              onds:Microseconds". Converted from kernel's uptime clock.

     0x7      Day Time Units (d) - "Days:Hours:Minutes:Seconds:Millisec-
              onds:Microseconds". Converted from kernel's uptime clock.

     0xF      No Time Units (-) - No time units, displayed as "-".

     Additive Options:

     0x10     Append output logging to /Library/Logs/FireWireKPrintf.log.

     0x100    Open log file with Only valid with "-o".

     0x800    Create a new log file, rather than append. Only valid with "-o".

     0x8000   Prefix logger machine's ID to each log.
     For example, if you wish to display microsecond time units with padding,
     synchronous mode enabled, and verbose printing disabled, the target's
     boot-args would be as follows: "debug=0x14e fwkpf=0x114". On the target,
     run the following in % sudo nvram boot-args="debug=0x14e

     If not defined, the "fwkpf" variable defaults to "0x004."


     Once the viewer is running, he target machine is logging, and both
     machines are connected with a FireWire cable, you will see output similar
     to the following:

           % fwkpfv
           Welcome to FireWireKPrintf (viewer x.x.x).
           c>50.097255 AppleFWOHCI_KPF version x.x.x
           c>55.110783 AppleFWOHCI_KPF (re)initialized
           c>55.110793 Log saver
           c>55.129614 in.c: warning can't plumb proto if=fw0 type 144

     'Welcome to FireWireKPrintf (viewer x.x.x)'
          signifies viewer tool start correctly. If multiple interfaces are
          present on the debugger machine, it will give an interface count.

     'AppleFWOHCI_KPF version x.x.x'
          signifies the AppleFireWireKPrintf kext has (re)initialized the
          FireWire hardware for use in a FireWIreKPrintf manner.

     'FWKPF: Time Format->...'
          displays the time format declared in the target's boot-args. See the
          "Options" section of this document to select a different time for-

          displays the time at which the kprintf call was logged. Prefixed
          with the letter that corresponds to the time formats listed above.
          The format of this time log is displayed upon start and can be
          changed in the target's boot-args. See above.

     '... in.c: warning can't...'
          the const char * string from the kprintf() call; the log. (This is a
          normal log.)


     If you are seeing the following symptoms:

     There is no output from the fwkpfv tool on the second machine:
           -   Make sure the two machines are connected with a good FireWire
           -   Run "nvram boot-args" and verify that the boot-args are set
           -   Be sure you're using the new fwkpfv utility, version 2.1 or

     The machine hangs at boot:
           -   Sometimes the console will hang at boot when there is a high
               volume of logging to screen. Try booting in non-verbose mode or
               limiting the volume of logging. Remove the "-v" from your
               machine's boot-args. Or remove "io=0x80".


     To disable the FireWireKPrintf, delete the target machine's boot-args.
     Within run the following:
           -   % sudo nvram -d boot-args
           -        OR set the boot-args variable to your previous setting.
           -   Restart to target Mac.


   Other debug/boot-arg options:
     For more information on the debug flags, please see Technical Note
     TN2118. Setting the boot-arg variable "io" to "0x80" will turn on a sig-
     nificant volume of power management logging, which may be useful while
     debugging sleep/wake issues. Similarly, adding the "-v" argument to the
     boot-args will enable Mac OS X's verbose mode. This may be useful for
     watching local logging during boot or shutdown. For example, to add power
     management logging and verbose mode:
           % sudo nvram boot-args="debug=0x8 io=0x80 -v"

   The timestamps for very early boot logs are inconsistent:
     FireWireKPrintf tries to catch kprintf calls as soon as its start() rou-
     tine is called. All kprintf calls after this point will be saved until
     the FireWire hardware has been initialized completely (which is also
     early in the boot process), however, the timestamps for these very early
     logs will reference the time they were sent via FireWire, not when
     kprintf() was called. All timestamps can be assumed accurate after the
     log from FireWireKPrintf that reads something similar to:
           FWKPF: Time Format->...

   The timestamps for very early wake logs are inconsistent:
     Similar to very early boot logs, kprintf() calls by the kernel very early
     upon wake will be saved and sent after the FireWire hardware has had time
     to initialize. Likewise, the timestamps for these early logs may reflect
     a yet-to-be-initialized cpu time. These timestamps will be extremely
     large and clearly recognizable.

   Synchronous or Non-Synchronous?:
     With exception to the two cases above (very early boot and very early
     sleep) when the FireWire hardware cannot be initialized without stopping
     kernel progression, all FireWireKPrintf logs are sent synchronously. This
     means that if the log is sent successfully, it is guaranteed to be on the
     wire before the call returns. If the log cannot be sent, an error will be
     written to system.log.

   How do I know if I have enabled FireWireKPrintf and have 'normal' FireWire
     The "FireWire" tab of "/Applications/Utilities/System" will
     allow you to see if FireWireKPrintf has disabled normal FireWire ser-
     vices. To this end, if FireWire is disabled, unplug any FireWire cables
     and restart the Mac to restore normal FireWire services. Additionally, be
     mindful to restart machines that have dropped into logging mode as soon
     as you have finished using FireWireKPrintf logging.

   My boot-args disappeared unexpectedly:
     Some applications, such as the Startup Disk preference pane, set the
     boot-args themselves. Therefore, it is always best to boot to the parti-
     tion you wish to debug, set the boot-args, and then restart.

   My FireWire drive mounts on a second machine and then disappears off the
     When a viewer Mac is connected to a logging (target) Mac, all normal
     FireWire services stop, including FireWire disk access. It may take a few
     moments for the disk to disappear on the logging Mac, but once you have
     connected a viewer Mac, it will be impossible to use a FireWire hard disk
     without restarting.

   I see an error when I first connect:
     The following log is often shown when you first connect:
           in.c: warning can't plumb proto if=fw0 type 144 error=17
     It is a normal log from a different part of the system and should not be
     of any concern.

   Compatibility with Intel and PPC:
     FireWireKPrintf works on both Intel and PowerPC based Macs. The inte-
     grated FireWireKPrintf and fwkpfv is new for Leopard and is not included
     in any previous OS release.

   Other FireWire Devices:
     To avoid conflicts it is best not to have other FireWire devices plugged
     into the host or target machines while using FireWireKPrintf. Having more
     than 2 nodes total (i.e. the two CPUs) may cause unexpected results.

   Logging from multiple machines:
     The fwkpfv utility is able to receive logging from multiple machines.
     Connecting more than one logging target machine to a viewer will result
     in individual Terminal windows showing machine specific logs. A full,
     unparsed log is saved to "/Library/Logs/fwkpf.log". You may also force
     machine ID prefixation to each log by specifying the "-i" flags to

   Using FireWireKPrintf with FireWireKDP:
     FireWireKPrintf is compatible with FireWireKDP. To use both, it is recom-
     mended to set the boot-args using the following command: % sudo nvram
     boot-args="debug=0x14e kdp_match_name=firewire" Of course, you may modify
     or add boot-args to suit your needs (see note above).

   How do I clear the viewer?:
     Remember, you can clear the scrollback buffer of by select-
     ing "Clear Scrollback" (or Cmd-K) from the "Scrollback" menu.

   Why do I see different logging with different machines?:
     The "built-in" kprintf output is target machine specific. This is due to
     special casing of hardware and other states. It may also vary with oper-
     ating system version and even kext versions. Remember, a developer can
     change their kprintf() calls at any time.

   Can I see more logging?:
     Most Macs have the ability to output a significant volume of power man-
     agement logging, which may be useful while debugging sleep/wake issues.
     Many options are defined in <Kernel/IOKit/IOKitDebug.h>.

   What about FireLog?:
     FireLog and FireWireKPrintf are different, both in theory and practice.
     FireLog is a high speed logging system which requires a framework. Most
     importantly, FireLog uses a buffering system (in a pull manner) to pre-
     vent the loss of logs during high logging volume or low processing time.
     Conversely, FireWireKPrintf employs a push method of sending each log
     onto the wire as soon as it is available. Furthermore, FireWireKPrintf is
     available sooner in the kernel's startup. FireLog is an excellent solu-
     tion if you need high speed logging.


             is installed as part of the Mac OS X Developer Tools.



Mac OS X                      September 15, 2008                      Mac OS X

Mac OS X 10.9 - Generated Sat Oct 12 11:18:01 CDT 2013
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