Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 4/01/2024
Public

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5.5.6.4. DLL Functionality

The DLL integrated in the combo PHY module is used to address the asynchronous nature of the flash devices during data transfer. The delay compensation circuitry supports the following features:

  • Programmable read clock delay specified as a percentage of a clock cycle
  • Programmable write data delays specified as percentages of a clock cycle
  • Delay compensation circuit re-sync circuitry activated during refresh cycles to compensate for temperature and voltage drift
  • Separate delay chains for each DQS read signal from the Flash devices

The delay compensation circuitry relies on a primary/secondary approach. There is a primary (master) delay line which is used to determine how many delay elements constitute a complete cycle. This count is used, along with the programmable fractional delay settings, to determine the actual number of delay elements to program into the secondary (slave) delay lines. The primary and secondary delay lines are identical. This approach allows the memory controller to observe a clock and then delay other signals by a fixed percentage of that clock.

The delay compensation process is described in the steps below:

  1. Determine the number of delay elements needed to capture an entire clock cycle.
  2. Determine the number of delay elements needed to delay the read DQS and write data from the programmable read and write delay parameters.
  3. Configure and design the delay chains.

The block diagram of the DLL in the PHY is shown in the following figure. The DLL generates the reference clocks for the DQ and DQS signals during write operations. This also generates the delayed signals for DQS and DQS commands in the read data path. The DLL locking mechanism and some supported debug features are described in the following sections.

Figure 155. DLL Block Diagram