BCM4390DKWBGT Datasheet, PDF (33/78 Pages) Cypress Semiconductor – WICED™ Wi-Fi IEEE 802.11 b/g/n SoC with Embedded Application Processor

BCM4390 Advance Data Sheet
IEEE 802.11n MAC
Wired Equivalent Privacy
The wired equivalent privacy (WEP) engine encapsulates all the hardware accelerators to perform the
encryption and decryption, and MIC computation and verification. The accelerators implement the following
cipher algorithms: legacy WEP, WPA TKIP, and WPA2 AES-CCMP.
The PSM determines, based on the frame type and association information, the appropriate cipher algorithm
to be used. It supplies the keys to the hardware engines from an on-chip key table. The WEP interfaces with
the TXE to encrypt and compute the MIC on transmit frames, and the RXE to decrypt and verify the MIC on
receive frames.
Transmit Engine
The transmit engine (TXE) constitutes the transmit data path of the MAC. It coordinates the DMA engines to
store the transmit frames in the TXFIFO. It interfaces with WEP module to encrypt frames, and transfers the
frames across the MAC-PHY interface at the appropriate time determined by the channel access mechanisms.
The data received from the DMA engines are stored in transmit FIFOs. The MAC supports multiple logical
queues to support traffic streams that have different QoS priority requirements. The PSM uses the channel
access information from the IFS module to schedule a queue from which the next frame is transmitted. Once
the frame is scheduled, the TXE hardware transmits the frame based on a precise timing trigger received from
the IFS module.
The TXE module also contains the hardware that allows the rapid assembly of MPDUs into an A-MPDU for
transmission. The hardware module aggregates the encrypted MPDUs by adding appropriate headers and pad
delimiters as needed.
Receive Engine
The receive engine (RXE) constitutes the receive data path of the MAC. It interfaces with the DMA engine to
drain the received frames from the RXFIFO. It transfers bytes across the MAC-PHY interface and interfaces with
the WEP module to decrypt frames. The decrypted data is stored in the RXFIFO.
The RXE module contains programmable filters that are programmed by the PSM to accept or filter frames
based on several criteria such as receiver address, BSSID, and certain frame types.
The RXE module also contains the hardware required to detect A-MPDUs, parse the headers of the containers,
and disaggregate them into component MPDUS.
Interframe Space
The interframe space (IFS) module contains the timers required to determine interframe space timing including
RIFS timing. It also contains multiple backoff engines required to support prioritized access to the medium as
specified by WMM.
The interframe spacing timers are triggered by the cessation of channel activity on the medium, as indicated
by the PHY. These timers provide precise timing to the TXE to begin frame transmission. The TXE uses this
information to send response frames or perform transmit frame-bursting (RIFS or SIFS separated, as within a
TXOP).
BROADCOM ®
February 5, 2014 • 4390-DS103-R
WICED Wi-Fi IEEE 802.11 SoC w/Embedded App Processor
Page 32
BROADCOM CONFIDENTIAL