* detect which Super I/O chip is soldered onto your mainboard,
* at which configuration port it's located (usually 0x2e or 0x4e), and
* dump all register contents of the Super I/O chip, together with the
default values as per datasheet (to make comparing the values easy).
It is mainly used for coreboot development purposes (see coreboot.org for details on coreboot), but it may also be useful for other things.
The list of supported Super I/O chips is available at http://coreboot.org/Superiotool#Supported_devices, but it can also be viewed by running superiotool -l.
$ superiotool -d
Found SMSC FDC37N769 (id=0x28, rev=0x01) at 0x3f0
idx 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11...
val 20 90 80 f4 00 00 ff 00 00 00 40 00 0e 28 01 00 00 00...
def 28 9c 88 70 00 00 ff 00 00 00 00 00 02 28 NA 00 00 80...
The idx fields contain the register numbers/indexes of the Super I/O, the val fields contain the contents of the respective register as read from the Super I/O, and the def fields contain the default values for the respective register, as specified in the datasheet.
The numbers in the output are all in hex format, and some special values may also occur: NA stands for not available (i.e., the datasheet doesn't specify a default value for the respective register), RR means reserved (the datasheet explicitly marks this register as reserved), and MM means misc, which can mean several things. It's recommended to consult the datasheet for detailed information about the MM fields.
The verbose output will not only list for which type of Super I/O the tool is scanning, but also at which configuration port it's probing, and which Super I/O initialization sequence is used. If no Super I/O was detected in a probing run, the returned output will be shown, as it may be useful for figuring out which (currently unrecognized) Super I/O chip this may be.