Intersil's station firmware for Prism2 chipset supports a so called HostApMode in which the firmware takes care of time critical tasks like beacon sending and frame acknowledging, but leaves other management tasks to host computer driver. 

This driver implements basic functionality needed to initialize and configure Prism2-based cards, to send and receive frames, and to gather statistics. %%% 
In addition, it includes an implementation of following IEEE 802.11 functions: 
* authentication (and deauthentication),
* association (reassociation, and disassociation),
* data transmission between two wireless stations,
* power saving (PS) mode signaling 
* and frame buffering for PS stations. 

The driver has also various features for development debugging and for researching IEEE 802.11 environments like access to hardware configuration records, I/O registers, and frames with 802.11 headers.

Source: (http://hostap.epitest.fi/ http://hostap.epitest.fi/)

See also HostAP