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Posts tagged with 'tools'

Colin Ian King

Dumping UEFI variables

UEFI variables in Linux can be found in /sys/firmware/efi/vars on UEFI firmware based machine, however, the raw variable data is in a binary format and hence not in a human readable form.   The Ubuntu Natty firmware test suite contains the uefidump tool to extract and decode the binary data into a more human readable form.

To run, use:

sudo fwts uefidump -

and you will see something similar to the following:

Name: AuthVarKeyDatabase.
  GUID: aaf32c78-947b-439a-a180-2e144ec37792
  Attr: 0x17 (NonVolatile,BootServ,RunTime).
  Size: 1 bytes of data.
  Data: 0000: 00                                               .

Name: Boot0000.
  GUID: 8be4df61-93ca-11d2-aa0d-00e098032b8c
  Attr: 0x7 (NonVolatile,BootServ,RunTime).
  Active: Yes
  Info: Primary Master Harddisk
  Path: \BIOS(2,0,Primary Master Harddisk).

Name: Boot0001.
  GUID: 8be4df61-93ca-11d2-aa0d-00e098032b8c
  Attr: 0x7 (NonVolatile,BootServ,RunTime).
  Active: Yes
  Info: EFI Internal Shell
  Path: \Unknown-MEDIA-DEV-PATH(0x7)\Unknown-MEDIA-DEV-PATH(0x6).

Name: Boot0003.
  GUID: 8be4df61-93ca-11d2-aa0d-00e098032b8c
  Attr: 0x7 (NonVolatile,BootServ,RunTime).
  Active: Yes
  Info: ubuntu
  Path: \HARDDRIVE(1,22,9897,0f52a6e132775546,ab,f6)\FILE('\EFI\ubuntu\grubx64.efi').

Name: Boot0004.
  GUID: 8be4df61-93ca-11d2-aa0d-00e098032b8c
  Attr: 0x7 (NonVolatile,BootServ,RunTime).
  Active: Yes
  Path: \ACPI(0xa0341d0,0x0)\PCI(0x2,0x1f)\ATAPI(0x0,0x1,0x0).

Name: BootOptionSupport.
  GUID: 8be4df61-93ca-11d2-aa0d-00e098032b8c
  Attr: 0x6 (BootServ,RunTime).
  BootOptionSupport: 0x0303.

Name: BootOrder.
  GUID: 8be4df61-93ca-11d2-aa0d-00e098032b8c
  Attr: 0x7 (NonVolatile,BootServ,RunTime).
  Boot Order: 0x0003,0x0000,0x0001,0x0004,0x0005,0x0006.

Name: ConIn.
  GUID: 8be4df61-93ca-11d2-aa0d-00e098032b8c
  Attr: 0x7 (NonVolatile,BootServ,RunTime).
  Device Path: \ACPI(0xa0341d0,0x0)\PCI(0x0,0x1f)\ACPI(0x50141d0,0x0)\UART(115200 baud,8,1,1)\VENDOR(11d2f9be-0c9a-9000-273f-c14d7f010400)\USBCLASS(0xffff,0xffff,0x3,0x1,0x1).

Name: ConInDev.
  GUID: 8be4df61-93ca-11d2-aa0d-00e098032b8c
  Attr: 0x6 (BootServ,RunTime).
  Device Path: \ACPI(0xa0341d0,0x0)\PCI(0x0,0x1f)\ACPI(0x50141d0,0x0)\UART(115200 baud,8,1,1)\VENDOR(11d2f9be-0c9a-9000-273f-c14d7fff0400).

Name: Setup.
  GUID: 038bcef0-21e2-49d1-a47c-b7257296b980
  Attr: 0x7 (NonVolatile,BootServ,RunTime).
  Size: 114 bytes of data.
  Data: 0000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  Data: 0010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  Data: 0020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  Data: 0030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  Data: 0040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  Data: 0050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  Data: 0060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  Data: 0070: 01 00   

The tool will try to decode the binary data, however, if it cannot identify the variable type it will resort to doing a hex dump of the data instead.

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Colin Ian King

The Firmware Test Suite (fwts) is still a relatively new tool and hence this cycle I've still been adding some features and fixing bugs.  I've been running fwts against large data sets to soak test the tool to catch a lot of stupid corner cases (e.g. broken ACPI tables). Also, I am focused on getting some better documentation written (this is still "work in progress").

New tests for the Oneiric 11.10 release are as follows:

    Sanity check tables against the MultiProcessor Specification (MPS). For more information about MPS, see the wikipedia MPS page.

    Dump annotated MPS tables.

    Sanity check Model Specific Registers across all CPUs. Does some form of MSR default field sanity checking.

    Very simple suspend (S3) power checks.  This puts the machine into suspend and attempts to measure the power consumed while suspended. Generally this test gives more accurate results the longer one suspends the machine.  Your mileage may vary on this test.

     Hex dump of the Extended BIOS Data Area.

In addition to the above, the fwts "method" test is now expanded to evaluate and exercise over 90 ACPI objects and methods.

One can also join the fwts mailing list by going to the project page and subscribing.

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Colin Ian King

The dwarves package contains a set of useful tools that use the DWARF information placed in the ELF binaries by the compiler. Utilities in the dwarves package include:

pahole: This will find alignment holes in structs and classes in languages such as C/C++.  With careful repacking one can achieve better cache hits.  I could have done with this when optimising some code a few years back...

codiff:  This is a diff like tool use to compare the effect a change in source code can create on the compiled code.

pfunct:  This displays information about functions, inlines, goto labels, function size, number of variables and much more.

pdwtags: A DWARF information pretty-printer.

pglobal:  Dump out global symbols.

prefcnt:  A DWARF tags usage count.

dtagnames: Will lists tag names.

So, using pglobal, I was able to quickly check which variables I had made global (or accidentally not made them static!) on some code that I was developing as follows:

pglobal -v progname

and the same for functions:

pglobal -f progname

Easy!  Obviously these tools only work if the DWARF information is not stripped out.

All in all, these are really useful tools to know about and will help me in producing better code in the future.

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Colin Ian King

Fragmentation on ext2/ext3/ext4 filesystems

If you want know how fragmented a file is on an ext2/ext3/ext4 filesystem there are a couple of methods of finding out.  One method is to use hdparm, but one needs CAP_SYS_RAWIO capability to do so, hence run with sudo:

sudo hdparm --fibmap /boot/initrd.img-2.6.38-9-generic

 filesystem blocksize 4096, begins at LBA 24000512; assuming 512 byte sectors.
 byte_offset  begin_LBA    end_LBA    sectors
           0   35747840   35764223      16384
     8388608   39942144   39958527      16384
    16777216   40954664   40957423       2760

Alternatively, one can use the filefrag utility (part of the e2fsprogs package) for reporting the number of extents:

filefrag /boot/initrd.img-2.6.38-9-generic
/boot/initrd.img-2.6.38-9-generic: 3 extents found

..or more verbosely:

filefrag -v /boot/initrd.img-2.6.38-9-generic
Filesystem type is: ef53
File size of /boot/initrd.img-2.6.38-9-generic is 18189027 (4441 blocks, blocksize 4096)
 ext logical physical expected length flags
   0       0  1468416            2048
   1    2048  1992704  1470463   2048
   2    4096  2119269  1994751    345 eof
/boot/initrd.img-2.6.38-9-generic: 3 extents found

Well, that's useful. So, going one step further, how many free extents are available on the filesystem? Well, e2freefrag is the tool for this:

sudo e2freefrag /dev/sda1
Device: /dev/sda1
Blocksize: 4096 bytes
Total blocks: 2999808
Free blocks: 1669815 (55.7%)

Min. free extent: 4 KB
Max. free extent: 1370924 KB
Avg. free extent: 6160 KB
Num. free extent: 1084

Extent Size Range :  Free extents   Free Blocks  Percent
    4K...    8K-  :           450           450    0.03%
    8K...   16K-  :            97           227    0.01%
   16K...   32K-  :            99           527    0.03%
   32K...   64K-  :           134          1475    0.09%
   64K...  128K-  :            96          2193    0.13%
  128K...  256K-  :            50          2235    0.13%
  256K...  512K-  :            30          2643    0.16%
  512K... 1024K-  :            36          6523    0.39%
    1M...    2M-  :            36         13125    0.79%
    2M...    4M-  :            14          9197    0.55%
    4M...    8M-  :            15         18841    1.13%
    8M...   16M-  :             8         17515    1.05%
   16M...   32M-  :             7         38276    2.29%
   32M...   64M-  :             3         39409    2.36%
   64M...  128M-  :             3         67865    4.06%
  512M... 1024M-  :             4        802922   48.08%
    1G...    2G-  :             2        646392   38.71%

..thus reminding me to do some housekeeping and remove some junk from my file system... :-)

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Colin Ian King

The Linux PCI core driver provides a useful (and probably overlooked) sysfs interface to read PCI ROM resources.  A PCI device that has a ROM resource will have a "rom" sysfs file associated with it, writing anything other than 0 to it will enable one to then read the ROM image from this file.

For example, on my laptop, to find PCI devices that have ROM images associated with them I used:

find /sys/devices -name "rom"

and this corresponds to my Integrated  Graphics Controller:

lspci | grep 02.0
00:02.0 VGA compatible controller: Intel Corporation Mobile GM965/GL960 Integrated Graphics Controller (primary) (rev 0c)

To dump the ROM I used:

echo 1 | sudo tee /sys/devices/pci0000\:00/0000\:00\:02.0/rom
sudo cat /sys/devices/pci0000\:00/0000\:00\:02.0/rom > vbios.rom

To disassemble this I used ndisasm:

sudo apt-get install nasm
ndisasm -k 0,3 vbios.rom | less

..and just use strings on the ROM image to dump out interesting text, e.g.

strings vbios.rom
00IBM VGA Compatible BIOS.

..and then used a tool like bvi to edit the ROM.

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Colin Ian King

Editing binaries using bvi

I don't want to start a vi vs emacs holy war, but I have found a wonderful binary editor based on the vi command set.  The bvi editor is great for tweaking binary files - one can tab between the hex and ASCII representations of the binary data to re-edit the data.

To install use:

sudo apt-get install bvi

As well as basic vi commands, bvi contains bit-level operations to and/or/xor/not/shift bits too.   One has to use ':set memmove' to insert/delete data as this is not enabled by default.

Anyhow, install, consult the man page and get editing binary files!

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Colin Ian King

SystemTap is a very useful and powerful tool that enables one to insert kernel debug into a running kernel.  Today I wanted to inspect the I/O read/write operations occurring when running some ACPI AML, so it was a case of hacking up a few lines of system tap to dump out the relevant state (e.g. which port being accessed, width of the I/O operation in bits and value being written or read).

So instead of spinning a bespoke kernel with a few lines of debug in, I use SystemTap to quickly write a re-usable script.  Simple and easy!

I've put the SystemTap script in my git repository for any who are interested.

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Colin Ian King

Normally when I see a problem to do with CPU, I/O, network or memory resource hogging I turn to my trusty tools such as vmstat, iostate or ifstat to check system behaviour.

I stumbled upon dstat today, which boasts to be "a versatile replacement for vmstat, iostat and ifstat.".  So let's see what it can do. First, install with:

sudo apt-get install dstat

Running dstat with no arguments displays CPU stats (user,system,idle,wait,hardware interrupts, software interrupts), Disk I/O stats (read/write), Network stats (receive,send), Paging stats (in/out) and System stats (interrupts, context switches).   Not bad at all. 

Dstat even highlights in colour the active values, so you don't miss relevant deltas in the statistics being churned out by the tool.  Colours can be disabled with the --nocolor option.

But there is more. There are a plethora of options to show various system activities, such as:

-l       load average
-m       memory stats (used, buffers, cache, free)
-p       process stats (runnable, uninterruptible, new)
--aio    aio stats (asynchronous I/O)
--fs     filesystem stats (open files, inodes)
--ipc    ipc stats (message queue, semaphores, shared memory)
--socket socket stats (total, tcp, udp, raw, ip-fragments)
--tcp    TCP stats (listen, established, syn, time_wait, close)
--udp    UDP stats (listen, active)
--vm          virtual memory stats (hard pagefaults, soft pagefaults, allocated, free) name but a few.  As it is, this already is more functional that vmstat, iostat and ifstat.   But that's not all - dstat is extensible by the use of dstat plugins and the packaged version of dstat comes shipped with a few already, for example:

--battery          battery capacity
--cpufreq          CPU frequency
--top-bio-adv  top block I/O activity by process
--top-cpu-adv  most expensive CPU process
--top-io      most expensive I/O process
--top-latency  process with highest latency

..and many more besides - consult the manual page for dstat to see more.

So, dstat really is a Swiss army knife - a useful tool to get to know and use whenever you need to quickly spot misbehaving processes or devices.

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Colin Ian King

The hwloc (hardware locality) package contains the useful tool lstopo. To install use:

sudo apt-get install hwloc

By default, lstopo will display a logical view of the system caches and CPU cores, for example:

To get a non-graphical output use:

lstopo -

Machine (1820MB) + Socket #0 + L3 #0 (3072KB)
  L2 #0 (256KB) + L1 #0 (32KB) + Core #0
    PU #0 (phys=0)
    PU #1 (phys=2)
  L2 #1 (256KB) + L1 #1 (32KB) + Core #1
    PU #2 (phys=1)
    PU #3 (phys=3)

lstopo is also able to output the toplogy image in a variety of formats (Xfig, PDF, Postscript, PNG, SVG and XML) by specifying the output filename and extension, e.g.

lstopo topology.pdf

For more information, consult the manual for hwloc and lstopo.

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Colin Ian King

hardinfo - look at hardware information in a GUI

Leandro Pereira has created hardinfo, a useful user-friendly GTK+ utility to browse the hardware information on one's machine. It also includes a bunch of benchmarking tools too.

To install, simply use:

apt-get install hardinfo

and run with Applications->System Tools->System Profiler and Benchmark or run from the command line using:


The tool presents information from /proc and /sys in a very easy to user and clean GUI. The view is broken into four categories:

Computer: OS, kernel modules, filesystem, display, environment variables, users.
Devices: CPU, memory, PCI, USB, printers, battery, sensors, input, storage, DMI, resources.
Network: Interfaces, IP connections, routing tables, ARP table, DNS servers, statistics, shares.
Benchmarks: Blowfish, CryptoHash, Fibonacci, CPU N-Queens, CPU FFT, FPU Raytracing.

Below are some sample views of my machine using hardinfo:

Quite a handy tool.

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Colin Ian King

Perf tool now in Ubuntu Lucid.

A few months ago I blogged about the perf tool and how useful it is to drill down into kernel and user space applications to analyse performance bottle necks. Well, thanks to Andy Whitcroft, the perf tool is now available in Ubuntu Lucid. Perf needs to be in lock-step with the kernel, which complicated the packaging of this tool.

To install, use:

sudo apt-get install linux-tools

and this installs the perf, perf-stat, perf-top, perf-record, perf-report and perf-list tools.

The author of perf, Ingo Molnar has written some basic instructions on driving perf in the tools/perf/Documentation/example.txt file. They should give one a feel of how to drive these tools.

For example, to examine google-chrome:

perf record google-chrome

... run a test and then exit, and then generate a summary of activity:

perf report

One can examine specific events in the system too. To get a list of available events use:

perf list

For example, to measure CPU cycles, number of instructions, context switches and kmallocs on google-chrome one uses:

perf stat -e cpu-cycles -e instructions -e context-switches -e kmem:kmalloc google-chrome

Performance counter stats for 'google-chrome':

15576472832 cycles # 0.000 M/sec
13466330277 instructions # 0.865 IPC
40791 context-switches # 0.000 M/sec
38602 kmem:kmalloc # 0.000 M/sec

18.062301718 seconds time elapsed

One more quick example, this time we record a call-graph (stack chain/backtrace) of the dd command:

perf record -g dd if=/dev/zero of=/dev/null bs=1M count=4096
and get the call graph using:

# Samples: 12584 # # Overhead Command Shared Object Symbol # ........ ............... ............................... ...... # 95.96% dd [kernel] [k] __clear_user | |--99.69%-- read_zero | vfs_read | sys_read | system_call_fastpath | __read --0.31%-- [...]
1.37% dd [kernel] [k] read_zero 0.87% dd [kernel] [k] _cond_resched | |--50.91%-- read_zero | vfs_read | sys_read | system_call_fastpath | __read

I recommend reading Ingo's example.txt and playing around with this tool. It is very powerful and allows one to drill down and examine system performance right down to the instruction level.

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Colin Ian King

Saving power on my HPMini (revisited on Lucid)

A while ago I blogged about power saving on my HPMini. Well, today I'm revisiting this using today's Lucid daily and I'm pleased to see that I can save a small amount of power with Lucid compared to Karmic. However, the difference is small - the inaccuracies of estimating power consumption using ACPI may be more significant.

My steps were as follows:

0. Run powertop for about 15 minutes on battery power and note down the recommended power saving tricks.

1. Blacklist Bluetooth, since I don't use this and it really sucks a load of power. To do so, add the following to /etc/modprobe.d/blacklist.conf

blacklist btusb

2. Enable HDA audio powersaving:

echo 1 > /sys/module/snd_hda_intel/parameters/power_save

3. Increase dirty page writeback time:

echo 1500 > /proc/sys/vm/dirty_writeback_centisecs

4. Disable the webcam driver (not sure exactly if this saves much power), add the following to /etc/modprobe.d/blacklist.conf

blacklist uvcvideo

5. Turn down the screen brightness (this saves 0.3 Watts)

6. Disable desktop effects to save some power used by compositing.

7. Disable cursor blinking on the gnome terminal to save 2 wakeups a second, using:

gconftool-2 --type string --set /apps/gnome-terminal/profiles/Default/cursor_blink_mode off

I managed to push the power consumption down to ~6.5 Watts which is an improvement of nearly 1 Watt from my tests on Karmic. Not bad, but I don't fully trust the data from the battery/ACPI and I really need to see how much extra battery life these tweaks give me when I'm using the machine on my travels.

On an idle machine I'm seeing > ~99.0% C4 residency, which is quite acceptable. Running powertop is always leads to insights to saving power, so kudos to Intel for this wonderful utility.

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Colin Ian King

HDA Analyzer

The HDA Analyzer tool that allows one to look at the raw HD-audio control data in an easy to user GUI. The instructions on how to download and use this tool are described at the HDA Analyzer page - they are as follows:

1. Fetch:

2. Run:


And browse...

This certainly takes the pain out of looking at the control information.

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Colin Ian King

The FirmWare Test Suite (fwts) is a tool I've been working on to do automatic testing of a PC's firmware. There can be a lot of subtle or vexing Linux Kernel/firmware issues caused when firmware is buggy, so it's useful to have a tool that can automatically check for common BIOS and ACPI errors. Where possible the tool will give some form of advice on how to fix issues or workaround firmware issues.

It's packaged up and in Maverick universe, you can install it using:

sudo apt-get install fwts

To see the tests available in the tool use:

fwts --show-tests

There are over 30 tests and I hope to expand this every time I find new firmware issues which can be diagnosed automatically in a tool.

To run a test use, for example the ACPI AML syntax checking test use:

sudo fwts syntaxcheck

There are categories of tests, for example, by default fwts will run batch mode tests which run without the need of user intervention. Some tests, such as checking the laptop lid works or hotkeys requires user intervention - these are interactive tests and can be invoked using:

sudo fwts --interactive

By default the tool will append the test results into a log file called results.log. This logs the date/time the test was run, the name of the test and the test results and hopefully some useful advice if a test fails.

I suggest checking out the manual page to see some examples how to fully drive this tool.

Quite a lot of the tests have been picked up from the core of, but I've added a bunch more tests, and expanded the types of errors it checks for and the feedback advice it reports. I've targeted fwts to run with the Maverick 2.6.35 kernel but it should work fine on Lucid kernels too. I've written fwts with command line driven test framework to run the tests mainly to allow fwts to easily plug into more powerful test frameworks.

If you want to run the tool from a bootable USB flash key, then one can download a i386 or amd64 image and dd it to a USB flash key.

For example:

sudo dd if=maverick-desktop-i386-fwts.img of=/dev/sdX

where /dev/sdX is the block device of your USB flash key

then boot off this USB flash key and let it run the tests. At the end it will automatically shutdown the PC and you can then remove the key. The key has a FAT formatted partition containing the results of the test in a directory named: fwts/ddmmyyyy/hhmm/results.log, where ddmmyyyy are the digits in the date and hhmm for the time the test was started.

The fwts PPA can be found in the Firmware Testing Team project and the source code is available in a git repository here.

I've also written a short OpenOffice presentation on the tool which also may prove instructive.

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Colin Ian King

Looking at a PC's option ROMs

An Option ROM is firmware called by the BIOS, for example the Video BIOS or a SCSI controller card. The BIOS Boot Specification requires that option ROMs are aligned to 2K boundaries and must begin with bytes 0x55 0xaa. After Power On Self Test (POST) the BIOS scans for option ROMs and if it finds a correct header executes the initialisation code at byte offset 0x3.

The Option ROM header is as follows:

Byte 0: 0x55
Byte 1: 0xaa
Byte 2: size of ROM in 512 byte pages
Byte 3: Option ROM entry point

To dump out the option ROMs, use the ree utility:

sudo apt-get install ree

..and run as follows:

sudo ree

..this will dump out all the option ROMs in the form: hexaddress.rom where hexaddress is the memory segment where the ROM is located. e.g. for my Video BIOS ROM, I get the file c0000.rom.

To disassemble this use ndisasm:

sudo apt-get install nasm

ndisasm -k 0,3 c0000.rom | less

..or just use strings on the ROM image to get an idea what the Option ROM is, e.g.

strings c0000.rom
00IBM VGA Compatible BIOS.
.. this case it is a VGA BIOS, and this makes sense as VGA BIOS ROMs normally start from segment c0000. On my Lenovo laptop I observe that the ROM contains the string "DECOMPILATION OR DISASSEMBLY PROHIBITED" which spoils our fun in finding out what the ROM is doing...

Anyhow, ree + ndisasm are useful tools for poking around your PCs option ROMs on Linux.

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Colin Ian King

Debugging ACPI using acpiexec

The acpiexec tool is an AML emulator that allows one to execute and interactively ACPI AML code from your BIOS.  The tarball can be downloaded from the ACPICA website  and built as follows:

1. Unzip and untar the acica-unix-20100304.tar.gz tarball.
2. cd into tools/acpiexec
3. run make

This should build acpiexec. Now for the fun part - executing your ACPI inside the emulator. To do this grab your ACPI tables and extract them using:

sudo acpidump > && acpixtract -a

Now load these tables into the emulator and run with verbose mode:

./acpiexec -v *.dat

Inside the emulator you can type help to navigate around the help system.  It may take a little bit of work to get familiar with all the commands available.

As a quick introduction, here is how to execute the battery information _BIF method.

1. Get a list of all the available methods, type:


on my Lenovo laptop the battery information method is labelled \_SB_.PCI0.LPCB.BAT1._BIF, so to execute this method I use:

execute \_SB_.PCI0.LPCB.BAT1._BIF
Executing \_SB_.PCI0.LPCB.BAT1._BIF
Execution of \_SB_.PCI0.LPCB.BAT1._BIF returned object 0x19669d0 Buflen 178
  [Package] Contains 13 Elements:
    [Integer] = 0000000000000001
    [Integer] = 0000000000000FA0
    [Integer] = 0000000000000FA0
    [Integer] = 0000000000000001
    [Integer] = 0000000000002B5C
    [Integer] = 00000000000001A4
    [Integer] = 000000000000009C
    [Integer] = 0000000000000108
    [Integer] = 0000000000000EC4
    [String] Length 08 = PA3465U
    [String] Length 05 = 3658Q
    [String] Length 06 = Li-Ion
    [String] Length 07 = COMPAL

So far so good. I single stepped through the code using the debug command on the method as follows:

debug \_SB_.PCI0.LPCB.BAT1._BIF

at each % prompt, one can press enter to step the next instruction. If the method requires arguments, these can be passed into the method by specifying them after the method name from the debug command.

To see any local variables used during execution, use the locals command. The list command lists the current AML instructions. The set commands allows one to set method data and interact with the debugging processes.

Hopefully this gives one a taste of what the emulator can do. The internal help is enough to get one up and running, and one does generally require the current ACPI specification to figure out what's happening in your ACPI tables.

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Colin Ian King

inotail - tail clone using inotify

I regularly use the tail command to look at the end of log files - generally I use the -f flag to follow (monitor and display) new entries that are appended to the log.

Tail will poll every second to see if the file size is changed and will act if data has been appended or the file has been truncated, and the poll interval is adjustable.  However, polling a file is plain ugly, it causes extra wakeup events and if one wants very fast updates then polling is not a good solution.

Hence, a better tool to use is inotail when following a file. Inotail uses inotify to only wake up inotail when a file has been modified, deleted or moved - hence no polling is required.  This also means inotail will output the changes to a file almost immediately - unlike tail which by default may wait almost a second before detecting a change.

To install inotail use:

sudo apt-get install inotail

..and use it the same was as tail.

UPDATE:  Pete Graner has also informed me that the tailf command is also an inotify based tail -f like replacement too. Just goes to show there are many ways of doing the same thing...

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Colin Ian King

A little used tool from the coreboot project is inteltool. This tool is useful for dumping the configuration space of Intel CPUs and for examining the Northbridge and Southbridge settings.

The debian package can be found in universe, and can be installed using:

sudo apt-get install inteltool

..and has to be run using sudo.

At the simplest level, it can be run to get CPU and Northbridge/Southbridge version information:

$ sudo inteltool
Intel CPU: Family 6, Model f
Intel Northbridge: 8086:2a00 (PM965)
Intel Southbridge: 8086:2815 (ICH8-M)

However, one can drill down a bit, for example to get a dump of the GPIO settings, use the -g flag, e.g.:

$ sudo inteltool -g
Intel CPU: Family 6, Model f
Intel Northbridge: 8086:2a00 (PM965)
Intel Southbridge: 8086:2815 (ICH8-M)

============= GPIOS =============

GPIOBASE = 0x1180 (IO)

gpiobase+0x0000: 0x99541d02 (GPIO_USE_SEL)
gpiobase+0x0004: 0xe0fa7fc2 (GP_IO_SEL)
gpiobase+0x0008: 0x00000000 (RESERVED)
gpiobase+0x000c: 0xe1aa5fc7 (GP_LVL)
gpiobase+0x0010: 0x00000000 (GPIO_USE_SEL Override (LOW))
gpiobase+0x0014: 0x00000000 (RESERVED)
gpiobase+0x0018: 0x00000000 (GPO_BLINK)
gpiobase+0x001c: 0x00000000 (GP_SER_BLINK)
gpiobase+0x0020: 0x00080000 (GP_SB_CMDSTS)
gpiobase+0x0024: 0x00000000 (GP_SB_DATA)
gpiobase+0x0028: 0x00000000 (RESERVED)
gpiobase+0x002c: 0x00001900 (GPI_INV)
gpiobase+0x0030: 0x00000146 (GPIO_USE_SEL2)
gpiobase+0x0034: 0x00540f70 (GP_IO_SEL2)
gpiobase+0x0038: 0x00540f74 (GP_LVL2)
gpiobase+0x003c: 0x00000000 (GPIO_USE_SEL Override (HIGH))

There are other options to dump out the RCBA, Power Management, Memory Controller, EPBAR, DMIBAR and PCIEXBAR registers as well as the CPU MSRs.

It's an excellent utility for digging into the configuration of any Intel PC.

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Colin Ian King

itop - look at top interrupt activity

When I want to see interrupt activity on a Linux box I normally use the following rune:

watch -n 1 cat /proc/interrupts

..which simply dumps out the interrupt information every second.  Another way is to use itop, which has the benefit that it outputs the interrupt rate which is lacking from my rune above.

To install, use:

sudo apt-get install itop

and to run, use:


The output is refreshed every second, and outputs something like the following:

INT                NAME          RATE             MAX
  0 [PIC-edge      time]   154 Ints/s     (max:   154)
 14 [PIC-edge      ata_]    16 Ints/s     (max:    16)
 18 [PIC-fasteoi   ehci]     4 Ints/s     (max:     4)
 22 [PIC-fasteoi   ohci]     2 Ints/s     (max:     2)
 29 [MSI-edge      i915]    38 Ints/s     (max:    38)
 30 [MSI-edge      iwl3]     6 Ints/s     (max:     6)

Unfortunately itop does truncate the interrupt names, but I'm not so worried about this - I generally want to see very quickly if a machine is suffering from interrupt saturation or is missing interrupts, which I can get from itop easily.

To see all interrupts, run itop with:

itop -a

And to run for a number of iterations, run with the -n flag, e.g.

itop -n 10

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Colin Ian King

blktrace graphs revisited

I blogged about seekwatcher a couple of days ago - it's great for producing charts from blktrace - however, I wasn't totally happy with the graph output. I wanted to be able to graph the data based on a tunable sample rate. So I've hacked up a script using awk and gnuplot to do this.

To run, suppose I've generated blktrace files readtest.blktrace.0 and readtest.blktrace.1 and I want a graph generated with 0.25 seconds per point, then do:

./generate-read-graph blktrace readtest.blktrace. 0.25

This generates a gnuplot file graph-reads.png, for example:

Now I'm happier with these results.

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