Extended double word accesses

摘要

A switching router memory map is organized as 64-bit wide double words. The bi-directional data bus is only 32-bits wide, so the Least Significant Words (LSW) are mapped to the even addresses and the Most Significant Words (MSW) are mapped to the odd address. When the host writes to the even address the 32-bit data is stored in the bidirectional data bus buffer. When the host writes to the odd address the entire 64-bit double word access is posted to the appropriate global access bus. When a read operation is performed from an even address the entire 64-bit double word access is performed by the appropriate global access bus. The LSW is available on the bi-directional data bus address data pins and the 32-bit MSW is buffered within the bi-directional data bus. The host can access the MSW by performing a read from the odd address.