A single device accesses the entire memory linearly. Access within a page (row) is very efficient, but switching pages can cause loss of efficiency. To minimize the loss, choose a mapping that will switch banks at page boundaries and, furthermore, alternate between different bank groups after each 64-byte DRAM command.
The chosen mapping is therefore: 16R-2B-1BG-7C-1BG-3C.
This mapping places a bank group bit after three column bits. This ensures that back-to-back DRAM commands target different bank groups and avoid same-group penalty. For comparison, the following table shows performance with other possible mappings.
Mapping | Efficiency | Mapping Type |
---|---|---|
16R-2B-1BG-7C-1BG-3C | 95% | Row-bank-column with bank group optimization |
16R-2B-2BG-10C | 54% | Simple row-bank-column |