SD Change Bus Speed

For SD card

Set block size to desired value.

reg_blocksize

xfer_blocksize

0x04

11:0

Block size value

Set up ADMA descriptor table (see Table: Setup ADMA2 Descriptor Table).

Set transfer mode with data direction and DMA enable.

reg_transfermode

xfermode_dmaenable | xfermode_dataxferdir

0x0C

4 and 1

0x11

Data cache (dcache) invalidate range.

Send CMD6.

Check for transfer completed.

reg_normalintrsts

All

0x30

15

Read operation

Clear the error interrupts (if any).

reg_errorintrsts

All

0x30

15:0

0xF3FF

Check transfer complete and clear if transfer is completed.

reg_normalintrsts

normalintrsts_xfercomplete

0x30

1

1b'1

Change clock frequency to 50 MHz (see Table: SD Clock Frequency Change).

Enable high speed.

reg_hostcontrol1

hostctrl1_highspeedena

0x28

2

1b'1

Read response 0.

reg_response0

command_response

0x10

15:0

Read

For eMMC card

Send CMD6 with eMMC high-speed argument and wait 2 ms.

Change clock frequency to 52 MHz.

Enable high speed.

reg_hostcontrol1

hostctrl1_highspeedena

0x28

2

1b'1

Program sequence to execute the tuning for high-speed cards

Set block size value.

reg_blocksize

xfer_blocksize

0x04

11:0

Block size value

Set the mode to data transfer.

reg_transfermode

xfermode_dataxferdir

0x0C

4

0x10

Set the execute tuning mode.

reg_hostcontrol2

hostctrl2_executetuning

0x3E

6

0x40

SD card: send CMD19 or eMMC card: send CMD 21.

Check if the reg_hostcontrol2 for tuning mask bit is not set.

Repeat the process until the tuning mask bit is not set.

Check the sampling clock select is set.

reg_hostcontrol2

hostctrl2_ samplingclkselect

0x3E

8

0x80

Set the desired clock frequency using Table: SD Clock Frequency Change, if sampling clock selection is set.

Program sequence for DLL tap delay for SD0 and SD1 controllers for high-speed cards.

Set the DLL reset value.

SD_DLL_CTRL

SD{0,1}_DLL_RST

0x0

2 and 18

0x4

Set the ITAPCHGWIN to gate the glitches in the line.

SD_ITAPDLY

SD{0,1}_ITAPCHGWIN

0x0

9 and 25

0x200

Set the ITAPDLYENA.

SD_ITAPDLY

SD{0,1}_ITAPDLYENA

0x0

8 and 24

0x100

Unset the ITAPCHGWIN.

SD_ITAPDLY

SD{0,1}_ITAPCHGWIN

0x0

9 and 25

Clear bit 9

Set the taps for the desired clock value.

SD_OTAPDLYSEL

SD{0,1}_OTAPDLYSEL

0x0

5:0 and 21:16

Desired value based on the clock.

Release DLL reset.

SD_DLL_CTRL

SD{0,1}_DLL_RST

0x0

2 and 18

Clear bit 2.

Set the taps for the desired clock value.

SD_OTAPDLYSEL

SD1_OTAPDLYSEL

0x0

21:16

Desired value based on the clock.

Unset the DLL reset value.

SD_DLL_CTRL

SD1_DLL_RST

0x0

18

Unset the bit 2.