SPRUIU1C July 2020 – February 2024 DRA821U , DRA821U-Q1
The sequence for changing SD Clock frequency is shown in Figure 12-2214.
(1) Execute the SD Clock Stop Sequence (see Figure 12-2213). If SD Clock supply to card is already stopped, skip this step.
(2) Clear MMCSD0_CLOCK_CONTROL[3] PLL_ENA bit to 0. If MMCSD0_CLOCK_CONTROL[3] PLL_ENA bit is not supported, this step has no effect and may be skipped.
(3) When MMCSD0_HOST_CONTROL2[15] PRESET_VALUE_ENA bit is set to 0, change clock parameters in the MMCSD0_CLOCK_CONTROL register. When MMCSD0_HOST_CONTROL2[15] PRESET_VALUE_ENA bit is set to 1, select Bus Speed Mode as described.
(4) Set MMCSD0_CLOCK_CONTROL[3] PLL_ENA bit to 1. If MMCSD0_CLOCK_CONTROL[3] PLL_ENA bit is not supported, this step this step has no effect and may be skipped.
(5) Wait until MMCSD0_CLOCK_CONTROL[1] INT_CLK_STABLE bit is set to 1. Clock will be stable in shorter time but timeout of this loop is defined as 150 ms. SD Clock Supply Sequence is required to provide clock to device (see Figure 12-2213).