3

Functional Overview

The WLAN Access Point is designed to operate in the

2.4GHz ISM frequency band, channels 1 to 11, as specified

by the FCC in the USA. The AP will also operate on

channels 12 through 14, where permitted by local regulatory

authorities. Radio equipment must be certified in a country

prior to use. Refer to Table 4 for a list of countries and

agencies that have approved the ISL36356A-APDK for

operation.

The Intersil PRISM II Chip Set allows for high level

integration; providing reduced size, increased throughput,

improved radio performance and faster time to market. The

WLAN Access Point implements Direct Sequence Spread

Spectrum DSSS technology that provides superior noise and

signal jamming immunity; including less severe impact from

unintentional radiators such as microwave ovens. By using

an Access Point, the wireless LAN can be set up to allow an

even greater number of users to interconnect, and to

increase the coverage area. The wireless LAN can be easily

connected into an existing wired LAN, allowing for easy

expansion of the service.

The ISL3856 Media Access Controller

(MAC) Protocol Handler

The ISL3856 ARM940 based MAC Processor and the MAC

Virtual Coprocessor (MVC) firmware are responsible for

running the IEEE802.11 protocol in the WLAN AP. The MVC

acts as a software emulated coprocessor to the ARM940

and runs completely separated from the operating system. It

provides an abstraction layer of the underlying hardware to

the operating system via a well-defined interface.

The MVC supports the following 802.11 functions:

• CSMA/CA (Carrier Sense Multiple Access with Collision

Avoidance) with Random Backoff

• WEP Security

• Short/Long Preamble with multirate

• RTS/CTS Handshake (Ready To Send/Clear To Send)

• MAC Level Acknowledgments (Media Access Control)

• Re-Transmission of Unacknowledged Frames

• Duplicate Detection and Rejection

• Broadcast and Multicast Frames

• Fragmentation and Re-Assembly

• Supports clients Power save mode

• Timestamp Synchronization

• DCF (Distributed Coordination Function)

The Linux Operating System

The ARM940 based MAC processor hosts a complete Open

Source Linux operating system, offering a flexible and

extensible platform for feature development. Due to the large

availability of different Linux based applications in the Open

Source community, it is easy to add new features to the AP,

reducing time to market.

A special embedded version of the Linux operating system,

uClinux, is running on the ISL3856. It is tailored to run on the

ARM940 processor and optimized for size. The uClinux

Application Programmers Interface (API) is the same as the

standard Linux API. The ISL36356A platform offers the

following basic functions:

• DHCP client/server

• Configuration via Web Interface and SNMP

• Simple and Failsafe Firmware Upgrade via Web Interface

• Wi-Fi Protected Access (WPA)

•802.1x Security

• Wireless Distribution System

• Routing, NAPT and firewall support

• PPPoE

• VPN Passthrough (PPTP)

• 802.1d Spanning Tree Protocol (STP)

Adding features to the development platform can be done by

taking applications that are available in the Open Source

community and port them to the platform. Porting

documentation is available to assist in this task. Applications

can also be made from scratch, so they can be kept closed

source.

The table below lists the resources that are available for

adding new applications to the basic design. In normal

operation, approximately 50% of the processor cycles of the

ARM940 are consumed by the MVC. The remaining capacity

is available for Linux and the applications. Because all

applications are stored in Flash in a compressed format, the

available Flash is calculated for both compressed and

uncompressed files.

For starting development on the Linux based platform, a

complete development environment is shipped with the

product, including documentation describing the setup of a

development system.

The complete hardware and software of the system are

pretested which ensures a stable development platform.

TABLE 2. AVAILABLE RESOURCES

MEMORY

CONFIGURATION

AVAILABLE

RAM

AVAILABLE FLASH

(COMPRESSED /

UNCOMPRESSED)

2Mbyte Flash

8Mbyte RAM

~1.2Mbyte

~16kbyte / 32kbyte

4Mbyte Flash

16Mbyte RAM

~9.2Mbyte

~2.0Mbyte / 4.0Mbyte

ISL36356A-APDK