External Memory Interface Handbook Volume 3: Reference Material

ID 683841
Date 7/24/2019
Public
Document Table of Contents

3.9.5.3. Efficiency Impact

The Periodic OCT recalibration engine must interrupt user traffic for a short period of time in order to update I/O buffer termination settings.

The exact flow of operations executed by the recalibration engine that affects memory traffic is described below:

  1. Enter Self-Refresh Mode. The EMIF calibration CPU triggers self-refresh entry on the hard memory controller. The controller flushes all pending operations, precharges all banks and issues the self-refresh command. This operation introduces a delay of approximately 25 Memory clock cycles (precharge all and self-refresh entry commands).
  2. Confirm Self-Refresh Mode. The EMIF calibration CPU polls the hard memory controller to confirm that the clocks have stopped. This operation introduces no delay.
  3. Issue codeword update. The EMIF calibration CPU triggers user-mode OCT logic to update code words. This operation introduces a delay of 50-100ns, depending on the device speed grade.
  4. Allow Exit Self-Refresh Mode. The EMIF calibration CPU enables automatic self-refresh exit logic. This operation introduces a delay of 50-100ns, depending on the device speed grade.
  5. Wait for Memory Traffic. The hard memory controller waits for an incoming read or write command on the Avalon bus. The delay introduced by this operation varies, depending on the user application.
  6. Exit Self Refresh Mode. The hard memory controller issues the Self-Refresh Exit command and a simultaneous memory-side RZQ calibration (ZQCS) command. The delay introduced by this operation varies according to the device speed bin (up to ~1000 memory clock cycles for fastest memory devices).

The efficiency impact on throughput-sensitive work loads is less than one percent, even under worst-case scenarios with all banks active. However, be aware that the first command issued after the hard memory controller exits self-refresh mode will incur the latency overhead of waiting for the memory DLL to re-lock when the Self-Refresh Exit command is issued by the hard memory controller. Contact Intel® FPGA Technical Services for information on how to manually trigger or inhibit periodic OCT updates for applications that are sensitive to latency.

Did you find the information on this page useful?

Characters remaining:

Feedback Message