Visible to Intel only — GUID: hco1416492105379
Ixiasoft
Visible to Intel only — GUID: hco1416492105379
Ixiasoft
11.2.5. Command Queue Look-Ahead Depth
For example, if you set the command queue look-ahead depth value to 4, the controller can track 4 open pages. In a 4-bank interleaving case, the controller will receive repeated commands with addresses of bank A, bank B, bank C, and bank D. To receive the next set of commands, the controller issues a precharge command to exit the current page and then issues an activate command to track the new incoming page, leading to a drop in efficiency.
With the command queue look-ahead depth set to 8, the controller can track 8 open pages and overall efficiency is much improved relative to a command queue look-ahead value of 4.
There is a trade-off between efficiency and resource usage. Higher command queue look-ahead values are likely to increase bank management efficiency, but at the cost of higher resource usage. Smaller command queue look-ahead values may be less efficient, but also consume fewer resources. Also, a command queue look-ahead value greater than 4 may cause timing violations for interfaces approaching their maximum frequency.
To achieve an optimized balance of controller efficiency versus resource usage and frequency, you must understand your traffic patterns. You should simulate your design with a variety of controller settings to observe the results of different settings.