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AR# 16916

3.1 EDK OPB_DDR/PLB_DDR - Can I alias the memory space?

Description

General Description: 

I am trying to determine the C_BASEADDR and C_HIGHADDR parameter values and I have a related question: 

Is it possible (using this OPB_DDR/PLB_DDR) to map 256 MB (0x0000_0000 to 0x0FFF_FFFF) of memory space for DDR SDRAM while only having 64 MB of physical DDR SDRAM present?

Solution

For a 256 MB memory space to alias 64 MB physical memory, you can set C_BASEADDR = 0x0000_0000 and C_HIGHADDR = 0x0FFF_FFFF. Also, there is a section in the DDR design specification that describes how the DDR address is sliced from the PLB/OPB address bus. Refer to the section "Connecting to Memory" -> "Memory to FPGA Connections" -> "DDR Address Mapping".

AR# 16916
Date Created 09/03/2007
Last Updated 05/15/2014
Status Archive
Type General Article