The entire system consists of three main function blocks: The AVR as the central CPU running the high level network routines including the TCP/IP stack. The second main block is the compact flash WLAN card running all the low level network functions including encryption. The third block is a XC9572XL CPLD, a programmable logic device that forms the spi2cf interface between the AVRs SPI and the CF card. It is mainly doing the translation between the SPI interface used to connect to the AVR and the parallel interface used on the compact flash slot.
Wlan for AVR: [Link]