NOTE: this page is for archival only, see the note at the end of the page.

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carl9170 is the 802.11n USB driver with GPLv2 firmware for Atheros USB AR9170 devices.


The Otus driver

Atheros merged support for their USB AR9170 2-stream 802.11n chipsets into the Linux kernel on the v2.6.29 release through a staging driver called Otus. The shortcomings for this driver was it required its own custom supplicant and obviously the code quality was sub-par.

ar9170usb driver

Shortly after Otus was submitted into staging Johannes Berg put a lot of effort into rewriting the driver for proper upstream inclusion. Christian Lamparter simply took what was already there, added a few finishing touches to addressed upstream considerations and we got it merged on the 2.6.30 release under the ar9170usb name.

During this time a lot of good work went into stabilizing the driver to replace the staging Otus driver from Atheros. The project had ambitious hopes to completely supersede the original Atheros staging driver: Otus.

To achieve this all functionality, performance, stability and quality must have been equally matched. In the end this proved quite challenging even though Atheros was kind enough to provide detailed documentations, hardware specifications and most importantly, they actually released the firmware source code under GPLv2!

It took months to dig through all the code and during this time the ar9170usb driver project lost most of its momentum and changes to the driver where limited to simple USB IDs updates, API fix-ups and serious crash fixes.


Towards the beginning of 2010 a new shiny driver: carl9170usb started brewing with the main goal of replacing the existing driver and making use of only open firmware.

It took 1 year, 5 months, 9 days since this merge of ar9170usb upstream to release carl9170 with upstream inclusion intentions.

The carl9170 driver actually ends up not only replacing but superseding the staging Otus driver.


  • Supports High Throughput/802.11n up to PHY speeds
    • of 300Mbits (~ RL performance of max. 100Mbit/s tcp, udp goes to 130 and beyond)
  • Access-Point mode for legacy stations and a
    • few improvements for IBSS.
  • multi-rate retry support. In order to improve throughput
    • and better link stability.
  • fully-automatic recovery from a number of
    • previously fatal events.
  • an input-device for the WPS push button, which
    • is present on some devices on the market.
  • pseudo virtual interfaces
    • (useful for universal repeater mode, or multiple APs)
  • facilities for debugging, testing and data dumping
    • within the driver (DebugFS), or in an isolated userspace environment (carlu).
  • AES Offload in single AP and single Station mode.
  • and a few small bits:
    • firmware images are protected against:
      • - the use with the wrong driver and vice versa - random/non-malicious corruptions
    • configurable firmware build, thanks to Kconfig
      • and cmake.


Upstream wireless-testing.git patch:

GPLv2 Firmware binary

You can download the GPLv2 Firmware binary:

Firmware source code

You can get the firmware source code from:


The firmware source code comes with support for building the toolchain. Requirements for building everything:

  • make 2.8+
  • bison
  • flex
  • gperf
  • libUSB 1.0+
  • libSDL 1.2+

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