manpagez: man pages & more
man reg(1)
Home | html | info | man
reg(1)                    BSD General Commands Manual                   reg(1)


     reg -- hardware register and address space access


     reg [--verbose[=BOOL]] list [THING]
     reg [--verbose[=BOOL]] info [THING]
     reg [--verbose[=BOOL]] [--format FORMAT] read THING
     reg [--verbose[=BOOL]] [--format FORMAT] [--verify-writes[=BOOL]] write
     reg --help
     reg --version


     reg provides access to the registers and memory within the machine, rang-
     ing from CPU registers to those in chipsets and PCI devices, to physical
     memory and I/O space.  It is strictly a developer and engineering tool,
     and is not for the feint of heart - misuse can very easily panic your
     machine, or potentially even do permanent, physical damage.

     You can run reg as any user, but results may be suboptimal, and you will
     not be able to read or write anything.  In general you will always needs
     to run reg as root, typically via sudo(1).


     There are a handful of optional flags you may use, documented below.  All
     flags may be specified, regardless of which commands you subsequently
     use, excepting the special flags --help and --version which exit immedi-
     ately after being processed.

     Note that command line arguments are processed strictly in order.  That
     is, any flags you specify affect only subsequent commands, and only until
     overridden by a second use of those flags.  Since you may in fact use
     multiple commands in a single invocation, this can be very useful as you
     may specify different formats or options for differant commands.

     -f FORMATS
     --format FORMATS
              Specifies the format(s) to display values in.  This is a comma-
              separated list, where each entry is a format type, one of:

              default  Use the default format for the item.

              raw      Print the raw bytes straight to stdout.

                       Print the mnemonic of the value.  May be used at any
                       time, but only the values of register fields may have
                       mnemonics associated with them.  Prints an empty line
                       if no mnemonic is known.

              name     Print the name of the value.  May be used at any time,
                       but only the values of register fields may have names
                       associated with them.  Prints an empty line if no name
                       is known.

              data     Prints the value as 'data', that is each byte's value,
                       in order, in hex.  A `@' suffix is included before the
                       value to denote this particular format.  You may
                       optionally append a number after the word `data',
                       indicating how many bits of data to display between
                       spaces. e.g. `data32' will print the data in four byte
                       chunks such as `@0020ffee dd6590a1 0030dde0d'.

              ASCII    Prints the value as an ASCII string.  Characters which
                       are not valid ASCII will be printed as periods.

              UTF8     Prints the value as a UTF-8 string.  Characters which
                       are not valid UTF-8 will be printed as periods.

              UTF16    Prints the value as a UTF-16 string.  Characters which
                       are not valid UTF-8 will be printed as periods.

              string   Prints the value as a string, using whatever encoding
                       reg determines is most appropriate.  Characters which
                       are not valid in the encoding chosen will be printed as

              float    Prints the value as a number (or numbers, if the value
                       is longer than the word size) in the specified type.
                       You may abbreviated the types to just `u', `s' or `f',
                       respectively.  You may also use `-' or `+' to indicate

                       You may use an `e' prefix before `float' (or, abbrevi-
                       ated, just `e' by itself) to specify use of scientific

                       As unsigned is the default mode you may leave it out

                       Following the number type you may specify the base,
                       using any of `hexadecimal'/`hex'/`h',
                       `decimal'/`dec'/`d', `octal'/`oct'/`o' or
                       `binary'/`bin'/`b'`unsigned' and simply specify the

                       Lastly, after the base you may specify the word width
                       in bits, as a number. This can be used to divide up
                       large values (e.g. a whole section of memory) into
                       individual words, each one presented individually with
                       appropriate markup (e.g. `0x' prefixes) and with space
                       between them.

                       Note that characters in the output, such as in prefixes
                       or the letters A through F used in hexadecimal numbers,
                       are by default lowercase unless the first character of
                       either the number type or the number's base is
                       uppercase. e.g. `uhex32' implies lowercase, `Uhex32' or
                       `uHex32' implies uppercase.

              Note that each separate use of the --format option completely
              overrides any previous specifications.  Since argument ordering
              is strictly obeyed, this is useful as it lets you specify dif-
              ferent formats for different commands.

     --help   Prints brief usage information and exits.

              If used with no argument, enables verbose mode.  Otherwise
              enables or disables verbose mode based on BOOL, which may be any
              typical boolean specifier, e.g. `off', `true', `0', `yes', etc.

              In verbose mode additional information may be provided, or
              existing information provided in a more verbose fashion (e.g.
              with additional whitespace and other formatting niceties).  The
              most obvious example is the descriptions of things - by default
              only summaries are provided, if any, while in verbose mode the
              full description is shown if available.

              If used with no argument, turns on write verification.  Other-
              wise enables or disables write verification based on BOOL, which
              may be any typical boolean specifier, e.g. `off', `true', `0',
              `yes', etc.

              Write verification means that any values written are then imme-
              diately read back and compared, the write operation considered
              failed if the values differ in any way.  This can be useful in
              certain scenarios, though in general it's not something you want
              to use unequivocally - some registers simply don't read back the
              same as written, or intentionally change shortly after a write,
              or just generally over time, etc.  Also be aware that reads may
              have side-effects and so enabling verification may have unin-
              tended consequences for some registers.

              Prints version information and exits.


     There are four commands you can use to perform actions with reg:

     list     Lists all things matching THING (or, if THING is not specified,
              all devices and address spaces in the current system).  Listing
              is intended for perusing the contents of things and discovering
              what is available, not for providing specific information about
              items.  For that, use the `info' command.

     info     Provides detailed information about all things matching THING.
              This information may include things like defined settings (if
              THING specifies register fields), names and mnemonics, descrip-
              tions or summaries (depending on verbosity settings), etc.

              Like the `list' command, `info' may be used without a THING
              parameter.  However, in that case it provides information about
              the system itself, not all the devices and address spaces within

     read     Prints the value(s) of all things matching THING, whether regis-
              ters, register fields or sections of address spaces.  The
              value(s) are printed according to the format(s) specified by the
              most recent preceeding --format flag, or using the default for-
              mat if not explicitly defined.  The default format may vary
              based on many factors.  As such, if you are using reg program-
              matically you should always specify the desired format explic-
              itly, regardless of whether the default happens to be what you
              want at the current time.

     write    Sets the value of all things matching THING to VALUE . The
              values set will be printed to stdout in a similar way to reading
              values using the `read' command.  If write verification has been
              enabled using --verify-writes, any verification failures will
              result in the actual value being printed immediately after the
              value that was (supposedly) written.

     You may specify multiple commands, optionally interspersed with option
     flags, that will be executed in left to right order.  Note however that
     reg will stop and exit upon the first failure - including failures
     related to printing of results or interpretation of input, not just the
     raw hardware access itself - so be wary of sequences which might leave
     hardware in a bad state if aborted midway.

     The THING argument specifies what hardware to perform the operation on.
     It is a potentially complex pattern that can match multiple entities, but
     always homogenously - that is, you can select some number of devices, or
     some number of registers, but not both devices and registers at once.  As
     such, there are actually only several key modes:

     System   This is a special case that applies only to the `info' command
              when you do not in fact provide a THING argument - in that case
              the target is assumed as the system as a whole, and information
              such as its manufacturer, model name and number, etc provided.

     Devices  You may select devices in any of three ways:

              1.   Select all devices using an asterisk, i.e.  `*', or - for
                   the `list' command only - by not providing a THING argu-
              2.   Select a particular category of devices, listed below.
              3.   Select devices with names matching the provided argument,
                   in which you may use asterisks, `*', as wildcards.

              When requesting a specific category of devices you can option-
              ally specify particular devices within those categories by pro-
              viding further matching information in square brackets.  The
              form of this information varies by category, as detailed in the
              category list below.

              Known categories are:

              cpus     Logical processor cores.  You may use brackets to spec-
                       ify the logical core index of the particular processor
                       core of interest.

                             e.g. cpu[0]

              pci      PCI devices.  You may use the brackets to specify the
                       vendor ID, device ID, segment number, bus number,
                       device number and function number, in that order.  Each
                       number should be separated by a delimiter such as a
                       comma, a slash, a hyphen, a vertical bar or a colon.
                       You may intermingle delimiter styles however you wish.
                       You are also not required to provide all six values -
                       any not specified will simply be treated as if you'd
                       specified `*', meaning of course to match any value for
                       that attribute.

                             e.g. pci[0x1048:0xa13, */*/3/5]
                                  pci[0x1048, 0xa13]

              os       Operating systems.  Today there will naturally be just
                       one operating system, so the use of brackets is not
                       supported with this category.

              memory   Physical memory.  Today there is just one physical mem-
                       ory space, so the use of brackets is not supported with
                       this category.

              io       I/O space.  Today there is just one I/O space, so the
                       use of brackets is not supported with this category.

              models   Models of arbitrary devices.  This allows you to look
                       at any known type of device - that is, use the `list'
                       and `info' commands.  Models are abstract - even if
                       there are instances of that device in the current
                       machine - and so cannot be used with the `read' or
                       `write' commands.  You may specify the model of inter-
                       est within square brackets.

                             e.g. model[Core 2]
                                  model[Mac OS X 10.6]

                       Note that you can only model devices, not address spa-
                       ces - address spaces are a very low level abstraction
                       and as such do not have any meaningful information in
                       the abstract.

              You may select one or more registers within one or more devices
              by providing a device specifier as above, and then appending to
              that, separated by a period, the name of the register(s) of
              interest.  The name is in fact a glob pattern - that is, you may
              use an asterisk, `*', as a wildcard that matches any zero or
              more characters.

              You may also optionally select a specific bit range in square
              brackets.  Eventually this will mean the read or write operation
              applies only to that bit range, though today this does not work
              correctly.  It does however filter the fields that will match -
              only those fields that intersect the selected range will be con-
              sidered for further matching against the mnemonic/name pattern
              provided, if applicable.

              You may also enclose the pattern in double (or single) quotes in
              order to use spaces or prevent misinterpretation by your shell,
              as shown in the examples below.

                    e.g. model[Core 2 (Penryn)].*
                         pci[0x10de/0xa89].``Vendor Identifier''

     Fields   In the same way as selected registers within a device, you may
              select fields within a register.  The same glob pattern seman-
              tics apply for matching names or mnemonics, and again you may
              wish to quote the pattern to prevent misinterpretation by your

              Note also that, as documented in the Registers section above,
              you may restrict to set of fields matched to only those inter-
              sect a given bit range within the register.

                    e.g. cpu[1].IA32_FIXED_CTR_CTRL.*

     Address ranges
              You may access the raw address spaces of a device or address
              space by using a colon, `': followed by the address range of
              interest.  There are two types of address space - flat ones,
              like physical memory, and indexed ones, like register address
              spaces underlying processors.  You can think of flat address
              spaces as one-dimensional: the range 0 to 10 selects 11 bytes.
              Indexed address spaces are in this sense two-dimensional: the
              range 0 to 10 selects 11 entries in the address space, where
              each entry is one or more bytes deep, such that the total is at
              least 11 bytes and likely much more.

              As such you need to be aware which you are using, as they behave
              slightly differently.  A flat address space will read (or write)
              as one big stream of bytes.  An indexed address space will read
              as multiple individual values, and when written to will use the
              same VALUE for each index independently.

              You may specify the range of interest in a variety of formats,
              the most common two being via boundaries or via a location and
              length pair. The former style sees the two end points separated
              by a delimiter such as a colon or a hyphen, while the later
              separates the location and the length via a comma. i.e.
              `0x1000-0x10ff', `0x1000:0x10ff' and `0x1000,0x100' are all
              equivalent.  You may also select just a single index by provid-
              ing just one number.  You may also use formal range notation
              using square brackets and parenthesis.

                    e.g. memory:0x0-0x100
                         memory:[0x100, 0x1ff]
                         memory:{0x200, 0x100}
                         memory:(0x300, 256)
                         memory:[0x400, 0x500)


     While some address spaces can be accessed explicitly (memory, io) others
     can only be accessed implicitly via their corresponding devices (e.g.
     pci, cpu).  If those devices are missing, or not all such address spaces
     are covered by a device, there is no way to access those orphaned address

     Input does not pay any attention to the current format options (though in
     any case you should use appropriate prefixes like `0x' or `@' to remove

     You can provide raw input in an analagous way to raw output.  In a more
     general sense, you cannot provide input via stdin rather than a command
     line argument.

Darwin                         October 13, 2009                         Darwin

Mac OS X 10.7 - Generated Sun Aug 14 13:18:57 CDT 2011
© 2000-2021
Individual documents may contain additional copyright information.