Wireless Lan for AVR microcontrollers

Posted on Mar 11, 2013

The page is about equipping an Atmel AVR microcontroller based system with a Prism WLAN interface. This document is intended for people that already have experiences with the AVR microcontrollers and teaches them how to add a cheap but flexible WLAN interface to your AVR projects. At least two other approaches exist to accomplish this. Both of them are using the similar Prism chip based WLAN cards. But none of these projects is fully documented nor fully working. The approach being part of the Procyon AVRlib is a pure software solution. This means that the AVR does the entire compact flash communication timing in software.

Wireless Lan for AVR microcontrollers
Click here to download the full size of the above Circuit.

This is unfortunately slow, unreliable (due to an inexact timing) and consumes plenty of those precious IO ports on the AVR. Furthermore it lacks a description of the hardware needed. The second approach is a WLAN hardware add-on to the ethernut board. It uses PCMCIA WLAN card and an FPGA to achieve hardware supported reliable transfers, but the hardware is only partially documented and the entire project has been discontinued due to unsatisfying performance. Thus i decided to build my own system. I wanted it to be as small, simple and cheap as possible while leaving much of the AVR functionality for other use and allowing fast and reliable WLAN data transfers. The final design was based on a prism chipset based compact flash WLAN card which is connected to the AVR CPU using a programmable logic chip (CPLD) made by Xilinx. Since the CF card is attached to the AVR using the SPI interface the entire system is named the SPI2CF project. You can get the complete compact flash specification from the Compact Flash Association. The pros and cons of this solution presented here are: Pros: Reliable CF data transfers Simple and easy SPI AVR interfacing Fast transfers with low cpu impact Homebrew friendly hard and software (all required tools are free of charge) Can be used for other compact flash cards as well Support for uip TCP/IP stack Cons: Requires the ability to flash a CPLD Uses outdated WLAN hardware Why not use...

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