BCM4354 datasheet(79/192 Pages) CYPRESS

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IEEE 802.11ac Draft MAC

BCM4354 Data Sheet

BROADCOM CONFIDENTIAL

Broadcom®

October 15, 2014 • 4354-DS109-R

Page 78

The backoff engines (for each access category) monitor channel activity, in each slot duration, to determine

whether to continue or pause the backoff counters. When the backoff counters reach 0, the TXE gets notified,

so that it may commence frame transmission. In the event of multiple backoff counters decrementing to 0 at the

same time, the hardware resolves the conflict based on policies provided by the PSM.

The IFS module also incorporates hardware that allows the MAC to enter a low-power state when operating

under the IEEE power save mode. In this mode, the MAC is in a suspended state with its clock turned off. A

sleep timer, whose count value is initialized by the PSM, runs on a slow clock and determines the duration over

which the MAC remains in this suspended state. Once the timer expires the MAC is restored to its functional

state. The PSM updates the TSF timer based on the sleep duration ensuring that the TSF is synchronized to

the network.

The IFS module also contains the PTA hardware that assists the PSM in Bluetooth coexistence functions.

TSF

The timing synchronization function (TSF) module maintains the TSF timer of the MAC. It also maintains the

target beacon transmission time (TBTT). The TSF timer hardware, under the control of the PSM, is capable of

adopting timestamps received from beacon and probe response frames in order to maintain synchronization

with the network.

The TSF module also generates trigger signals for events that are specified as offsets from the TSF timer, such

as uplink and downlink transmission times used in PSMP.

NAV

The network allocation vector (NAV) timer module is responsible for maintaining the NAV information conveyed

through the duration field of MAC frames. This ensures that the MAC complies with the protection mechanisms

specified in the standard.

The hardware, under the control of the PSM, maintains the NAV timer and updates the timer appropriately based

on received frames. This timing information is provided to the IFS module, which uses it as a virtual carrier-

sense indication.

MAC-PHY Interface

The MAC-PHY interface consists of a data path interface to exchange RX/TX data from/to the PHY. In addition,

there is an programming interface, which can be controlled either by the host or the PSM to configure and control

the PHY.

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