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Go back –> Atheros Linux wireless drivers


ath the shared module between Atheros wireless drivers. It contains any shared common code. It currently only contains the common shared regulatory code and one common harware helper but can be extended to contain anything seen shared between all drivers, both 802.11n or legacy 802.11abg devices. The ath modules is currently shared and used between ath5k, ath9k*, ath6kl_* and carl9170.


Here is the TODO list for the common shared code for Atheros modules.


Atheros devices share the same regulatory implementation. All devices have a regulatory domain code programmed into their EEPROM. The programmed regulatory domain code can be of three kinds:

To better understand the nomenclatures used it helps to understand the conventions followed by the old Atheros regulatory group naming convention. Tendencies to follow “US” similar regulatory domains were given “FCC” prepend labels after the FCC, European regulatory domains used the “ETSI” prepend name after the ETSI, Asian countries tended to fit under “MKK” under the Japanese regulatory agency (I forget what this stands for), “APL” which I believe stands for “Asia, Pacific and Latin America”. Numbers were appended at the end of each group label for 5 GHz groups, and letters for 2 GHz band group names.

Examples of 5 GHz regulatory band group names:

Each regulatory band group had an attached set of frequency ranges along with regulatory flags for the channels. Band groups could be put together to form a regulatory domain, containing one 5 GHz regulatory domain group, and a 2 GHz regulatory domain group.

Examples of regulatory domain groups:

Each regulatory domain group would also have an equivalent Conformance Test Limit (CTL) group. There are 3 CTL groups:

Customizing Atheros hardware

Vendors or manufacturers who may customize Atheros hardware may likely choose to enable their customers to use a wider range of frequencies or to use a higher max EIRP output. Certification would be done by these manufacturers and as such it is up to them to supply you with a custom regulatory database for its use. Typically a proprietary Linux driver would be provided with a customized “HAL” which allows more frequencies or higher EIRP. Since the upstream Linux drivers do not rely on a “HAL” anymore for regulatory purpose and instead rely on CRDA, manufacturers who customize hardware could simply just provide custom signed regulatory databases and a custom CRDA instead of providing a completely separate driver.

For details as to how to achieve a custom regulatory wireless-regdb and public key see the Custom_regulatory_information guidelines.

The 0x0 regulatory domain

The 0x0 value of a regulatory domain is to be used by Atheros devices to map to the “US”, always. This is as per Atheros documentation to manufacturers. Manufacturers wanting to enable users to use cards as “region free” should supply their own builds of CRDA and a signed regulatory database.

For more details you can refer to this thread:

EEPROM world regulatory domain

Atheros EEPROM can use 12 custom world regulatory domains:

5 GHz with world regulatory domain and beacon hints

All Atheros custom world regulatory domains have all 5 GHz channels marked with a passive scan flags. The non-DFS channels can have their passive scan flags lifted through a feature implemented in cfg80211 called “beacon hints”. For details on that please read the beacon hints documentation.

EEPROM ISO-3166-1-numeric code

The Atheros EEPROM regulatory domain can contain an ISO-3166-1-numeric country code. This may or not match the exact ISO3166-1-numeric country code, but usually does. Because it may not always match for the new regulatory infrastructure used in Linux we map the country to the ISO-3166-alpha2 country code.

Examples of possible country code numbers a card EEPROM can be programmed with:

EEPROM regulatory pairs

The Atheros EEPROM can use a regulatory pair group. Examples of regulatory pair groups:

The old way

The old way was to define all band groups (5 GHz and 2 GHz) in the driver code. Each band group would have a set of defined frequency ranges. 1)

The new way

We have extracted the regulatory domain definitions per ISO3166-alpha2 and converted them to human legible ASCII text file, used by the new Linux regulatory infrastructure. Each country therefore has a db.txt entry such as:

country EC:
        (2402 - 2482 @ 40), (N/A, 20)
        (5170 - 5250 @ 20), (6, 17)
        (5250 - 5330 @ 20), (6, 23), DFS
        (5735 - 5835 @ 20), (6, 30)

The custom regulatory domains are kept statically as part of the driver. The custom regulatory domains are the 12 custom world regulatory domains.

Regulatory pair regulatory domains are mapped to the first ISO-3166-alpha2 country.

Driver initialization

The device programmed EEPROM is read. We then determine if the regulatory domain code is a country regulatory domain COUNTRY_ERD_FLAG (0x8000) or a regulatory pair. Based on that, we determine whether we use an ISO3166-alpha2 country code for a regulatory_hint() or we use a static world regulatory domain.

In case of the absence of CRDA and because the kernel still has CONFIG_WIRELESS_OLD_REGULATORY (although deprecated) the ath module pre-initializes the wiphy channels to apply the default world regulatory domain (0x64). This is done done in ath_regd_init_wiphy() by using the cfg80211 provided wiphy_apply_custom_regulatory(). This is done because CONFIG_WIRELESS_OLD_REGULATORY is still present upstream and if not done would allow even “JP” channels to be used on cards designed for the “US”. Also, although the static world regulatory domain in cfg80211 is sufficient for complete world compliance Atheros has always supported a 5 GHz band which is a little more extended. The world regulatory domain is computed dynamically on a regular basis by using the intersection of all regulatory domains. Code for computing this can be found on intersection.c. This currently produces a 5 GHz band supporting the frequency ranges:

5170-5250 Channels [36-48]
5735-5835 Channels [149-165]

While Atheros' default world regulatory domain covers:

5140-5360 Channels [36-64]
5715-5860 Channels [149-165]

An Atheros world roaming card would then support channels 52, 56, 60, and 64 when world roaming, but by also enabling passive scan, no beaconing and requiring radar detection on them as well. The number of allowed HT40 channels would also increase to:

5180 HT40  +
5200 HT40 -+
5220 HT40 -+
5240 HT40 -+
5260 HT40 -+
5280 HT40 -+
5300 HT40 -+
5320 HT40 - 

This happens when your card has a world roaming regulatory domain. It should be also noted that if your card is world roaming your card will also remove passive-scan flag and no-beaconing flag restrictions if an AP is found locally on a channel and DFS is not required on that channel on the 5 GHz band.

Hidden SSIDs

Please read the regulatory documentation on hidden SSIDs. Hidden SSIDs can become a problem for cards that are world roaming. For QCA cards you can determine means your EEPROM regulatory matches one of the listed world regulatory domains. To verify you can issue a command as follows:

system@user:~$ dmesg | grep ath | egrep "regdomain|Country"
ath: EEPROM regdomain: 0x6a
ath: Country alpha2 being used: 00

You will see the 00 country code being used if your regulatory domain on your EEPROM is determined to be a world regulatory domain. For further reading on understanding any possible issues with hidden SSIDs be sure to read the regulatory documentation on hidden SSIDs.

1) this documentation section could be extended further