SPRACT9A September 2020 – May 2024 AM6526 , AM6528 , AM6546 , AM6548 , AM68 , AM68A , AM69 , AM69A , DRA821U , DRA821U-Q1 , DRA829J , DRA829J-Q1 , DRA829V , DRA829V-Q1 , TDA4AH-Q1 , TDA4AP-Q1 , TDA4APE-Q1 , TDA4VH-Q1 , TDA4VM , TDA4VM-Q1 , TDA4VP-Q1 , TDA4VPE-Q1
This application report describes how to perform software tuning with Multi-Media Cards (MMCs) at speed modes at or above 50 MHz (DDR50, SDR50, SDR104, HS200, HS400) on the AM65x, DRA80x, DRA82x, TDA4VM family of devices. This document describes why the tuning algorithm is needed and how it works to achieve a functional system.
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The read tuning algorithm is recommended by the SD Group and JEDEC Solid State Technology Association to compensate for timing variations due to a collection of system factors above 50 MHz high speed of operation. These factors include changes in silicon processes, operating temperature and voltage, PCB loading, as well as SD and eMMC slave device output timing.
During the read tuning process, the CLK-DAT latching position is adjusted through the delay module in single steps increments across a full range of 32 ratio elements. This adjustment can be done via automatic hardware tuning or manual software tuning. Limitations exist with the hardware tuning mechanism so the software tuning mechanism is the preferred method of implementation. This application report briefly describes the hardware tuning mechanism limitation and then goes over the software tuning algorithm in detail.
Hardware tuning is executed by setting MMCSDx_HOST_CONTROL2[6] EXECUTE_TUNING bit to ‘1’ and issuing CMD19/CMD21 repeatedly. The hardware then automatically sequences through all 32 delay ratios and selects the optimal one for functionality runs.
When the hadware tuning mechanism is used, you do not have visibility into the pass and fail result of each delay ratio elements, nor the final delay ratio element chosen to be utilized during functionality runs. This means a lack of visibility into the inner working of the hardware tuning module for debug needs. As a result, the software tuning algorithm is the recommended method of implementation on all systems.