AM6548: Power supply for SD card

Daisuke-san,

The RESETSTATZ is the warm reset signal; adding this gives you an option to reset the SD card without cold reset during functionality run.  If this functionality is not desired, you can use only MMC1_SD_EN for the reset control.

The dynamic voltage switching to reach UHS modes is only associated with the I/O lanes (VDDSHV_SD_IO).  On that note, there are errata associated with this sequence on SR1.0 (more info can be found here https://www.ti.com/lit/er/sprz452e/sprz452e.pdf), these are fixed on SR2.0 but wanted to highlight them in case you are using SR1.0 for development.

Best Regards,

Shiou Mei

Hi Daisuke-san,

That patch also removes "no-1-8-v; " DT property which is required to enable UHS mode (operates at 1.8 IO voltage).

The card sends S18A for CMD41 to indicate it supports voltage switching (for UHS mode). If the card already switched to UHS mode, sending CMD41 will not result in S18A set without a power cycle.

For example if the bootloader switched the card to UHS mode, the kernel during enumeration will see that the card does not support voltage switching, therefore no UHS mode without powercycle. However with power cycle, the card will set S18A indicating it supports voltage switching.

Thanks,

Kishon 

Daisuke-san,

Following up to what Kishon mentioned, even though you can skip routing RESETSTATZ, you will still need to route the MMC1_SD_EN signal to a power switch on your board; the power switch output can then be connected to the VDD pin of the SD card.  This adds capability to reset the SD card in case you need to go back to 3.3 V operation mode after 1.8 V voltage switching.

Thanks & Regards,

Shiou Mei