Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 7/19/2024
Public

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5.4.6.7.1. Tuning

SD Host Controller/Physical Layer Standard Specifications define UHS-I SDR104 speed mode, and the eMMC 5.1 Standard Specification defines HS200 and HS400 speed modes. These modes do not define the valid data window's position in respect to the clock. Instead, they define the valid window width and mandate that it must be sent from the device within 0 to 2 clock cycles.

These modes are expected to be operational after the procedure adjusts sampling point to the center of the floating valid data window. The procedure is similar for both standards. It has 40 iterations where the host sends the read tuning pattern command. In each iteration the data sampling point is tuned (increased incrementally). The goal is to cover fully at least one SDCLK clock period changing the sampling clock phase from 0 to at least 360 degrees with fixed step.

Each step begins with setting the sampling point, then the host controller sends command, then receives response and read data pattern.

When a step ends, the controller knows if it is successful (host controller could receive valid response and data pattern) or unsuccessful iteration (host detected a protocol error).

Based on post-tuning statistics of successful iterations, the hardware/software can set the sampling point close to the middle of the valid data window.

The tuning sequences looks slightly different with SD (Tuning Sequence for SD) and eMMC (Tuning Sequence for eMMC).

The figure below shows the moments when the host/PHY settings update is required during transition between speed modes and tuning.

Figure 147. Updating Settings When Tuning