There are several options to integrate custom logic with EDK system.
1. Use the dual port xps_bram to exchange the data, with port A connect to processor and port B connect to custom logic directly.
2. Use the xps_mch_emc, xps_epc or xps_gpio cores to interface and control the custom logic directly, this provides the I/O like access and even some burst features with emc core.
3. Use the "Create and Import Peripheral Wizard" to create a custom IP core directly, this wizard provides more advanced custom features to implement a custom IP. For details, refer to the "Creating Your Own Intellectual Property" part of "EDK Concepts, Tools, and Techniques " :
http://www.xilinx.com/support/documentation/sw_manuals/xilinx12_1/edk_ctt.pdf