5.1 MAC

The ATWILC3000A is designed to operate at low power, while providing high data throughput. The IEEE 802.11 MAC functions are implemented with a combination of dedicated datapath engines, hardwired control logic and a low-power, high-efficiency microprocessor. The combination of dedicated logic with a programmable processor provides optimal power efficiency and real-time response, while providing the flexibility to accommodate evolving standards and future feature enhancements.

The dedicated datapath engines are used to implement datapath functions with heavy computational requirements. For example, a Frame Check Sequence (FCS) engine checks the Cyclic Redundancy Check (CRC) of the transmitting and receiving packets, and a cipher engine performs all the required encryption and decryption operations for the WEP, WPA-TKIP, WPA2 CCMP-AES and WPA2 Enterprise security requirements.

Control functions, which have real-time requirements, are implemented using hardwired control logic modules. These logic modules offer real-time response while maintaining configurability through the processor. Examples of hardwired control logic modules are the channel access control module (implements EDCA/HCCA, Beacon TX control, interframe spacing and so on), protocol timer module (responsible for the Network Access vector, backoff timing, timing synchronization function and slot management), MAC Protocol Data Unit (MPDU) handling module, aggregation/deaggregation module, block ACK controller (implements the protocol requirements for burst block communication) and TX/RX control Finite State Machine (FSM) (coordinates data movement between PHY and MAC interface, cipher engine and the Direct Memory Access (DMA) interface to the TX/RX FIFOs).

The following are the characteristics of MAC functions implemented solely in software on the microprocessor:

  • Functions with high memory requirements or complex data structures. Examples include association table management and power save queuing.
  • Functions with low computational load or without critical real-time requirements. Examples include authentication and association.
  • Functions that require flexibility and upgradeability. Examples include Beacon frame processing and QoS scheduling.

Features

The ATWILC3000A MAC supports the following functions:

  • IEEE 802.11b/g/n
  • IEEE 802.11e WMM QoS EDCA/PCF multiple access categories traffic scheduling
  • Advanced IEEE 802.11n features:
    • Transmission and reception of aggregated MPDUs (A-MPDU)
    • Transmission and reception of aggregated MSDUs (A-MSDU)
    • Immediate block Acknowledgment
    • Reduced Interframe Spacing (RIFS)
  • IEEE 802.11i and WFA security with key management:
    • WEP 64/128
    • WPA-TKIP
    • 128-bit WPA2 CCMP (AES)
  • WPA2 Enterprise
  • Advanced power management:
    • Standard IEEE 802.11 Power Save mode
    • Wi-Fi alliance WMM-PS (U-APSD)
  • RTS-CTS and CTS-to-Self support
  • Either STA or AP mode in the infrastructure basic Service Set mode
  • Concurrent mode of operation
  • Independent Basic Service Set (IBSS)