BCM4354 datasheet(78/192 Pages) CYPRESS

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IEEE 802.11ac Draft MAC

BCM4354 Data Sheet

BROADCOM CONFIDENTIAL

Broadcom®

October 15, 2014 • 4354-DS109-R

Page 77

WEP

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, 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.

TXE

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.

RXE

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.

IFS

The 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).

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