BCM4330 Preliminary Data Sheet
MAC Features
PSM
The programmable state machine (PSM) is a micro-coded engine, which provides most of the low-level control
to the hardware, to implement the 802.11 specification. It is a microcontroller that is highly optimized for flow
control operations, which are predominant in implementations of communication protocols. The instruction
set and fundamental operations are simple and general, which allows algorithms to be optimized until very late
in the design process. It also allows for changes to the algorithms to track evolving 802.11 specifications.
The PSM fetches instructions from the microcode memory. It uses the shared memory to obtain operands for
instructions, as a data store, and to exchange data between both the host and the MAC data pipeline (via the
SHM bus). The PSM also uses a scratchpad memory (similar to a register bank) to store frequently accessed and
temporary variables.
The PSM exercises fine-grained control over the hardware engines, by programming internal hardware
registers (IHR). These IHRs are co-located with the hardware functions they control, and are accessed by the
PSM via the IHR bus.
The PSM fetches instructions from the microcode memory using an address determined by the program
counter, instruction literal, or a program stack. For ALU operations the operands are obtained from shared
memory, scratchpad, IHRs, or instruction literals, and the results are written into the shared memory,
scratchpad, or IHRs.
There are two basic branch instructions: conditional branches and ALU based branches. To better support the
many decision points in the 802.11 algorithms, branches can depend on either a readily available signals from
the hardware modules (branch condition signals are available to the PSM without polling the IHRs), or on the
results of ALU operations.
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.
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BROADCOM
BCM4330 Preliminary Data Sheet
April 28, 2011 • 4330-DS304-RI
Page 87
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