So here is how it works:

First compile...

gcc ath_info.c -o ath_info

then find card's physical address

lspci -v

02:02.0 Ethernet controller: Atheros Communications, Inc. AR5212 802.11abg NIC (rev 01)
        Subsystem: Fujitsu Limited. Unknown device 1234
        Flags: bus master, medium devsel, latency 168, IRQ 23
        Memory at c2000000 (32-bit, non-prefetchable) [size=64K]
        Capabilities: [44] Power Management version 2

address here is 0xc2000000

load madwifi-ng or madwifi-old if not already loaded (be sure the
interface is down!)

modprobe ath_pci

OR

call:
setpci -s 02:02.0 command=0x41f cache_line_size=0x10

to enable access to the PCI device.

and we run the thing...

./ath_info 0xc2000000

In order to change the regdomain to 0, call:

./ath_info -w 0xc2000000 regdomain 0

to change any PCI ID value, say:

./ath_info -w 0xc2000000 <name> X

with <name> ::= pci_dev_id | pci_vendor_id | pci_class |
                pci_subsys_dev_id | pci_subsys_vendor_id

With newer chipsets (>= AR5004x, i.e. MAC >= AR5213), Atheros introduced
write protection on the EEPROM.  On a GIGABYTE GN-WI01HT you can set
GPIO 4 to low to be able to write the EEPROM.  This depends highly on
the PCB layout, so there may be different GPIO used.  This program
currently sets GPIO 4 to low for a MAC >= AR5213, but you can override
this with the -g option:

./ath_info -g 5:0 -w 0xc2000000 regdomain X

would set GPIO 5 to low (and wouldn't touch GPIO 4).  "-g" can be given
several times.

The write function is currently not tested with 5210 devices.

Use at your own risk, entering a false device address will have really
nasty results!  Writing wrong values to the PCI ID fields may prevent
the driver from detecting the card!

Transmitting on illegal frequencies may violate state laws.  Stick to
the local regulations!

DISCLAIMER:
The authors are in no case responsible for damaged hardware or violation
of local laws by operating modified hardware.