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Connecting microSD and eMMC at same time?


I have an STM32MP157 discovery kit and we are considering using STM32MP157 at my work for a future PCBA we are creating.

We would like to connect an external UHS1 microSD slot to the STM32MP157, but for data collection writing at 100 MB/s. We would also like to connect a separate eMMC to SDMMC .

I see this text in Section 58.1 of the STM32157 reference manual which causes me to wonder if the current system would support this?

0693W000008woaWQAQ.pngDoes this mean the hardware can't every support the configuration we are desiring? Or the software somewhere like OpenSTLinux needs to be modified? Or is the information stale?

In other ST documentation, I see that we are able to configure booting from SDMMC1 or SDMMC2 which seems strange if the system can only support 1 "MMC" connected thing at a time.

Thank you,


ST Employee

Hi, the sentence you highlight in the reference manual is somewhat an old disclaimer related to some SDMMC IP supporting more than one card with one single instance of the IP (i.e. a kind of IO muxing under control of the SDMMC IP). This is not supported in STM32MP15 SDMMC IP.

But as we have 3 instance of SDMMC (SDMMC1, SDMMC2 and SDMMC3), there is no issue to support SD-Card and eMMC and SDIO (e.g. WLAN) at the same time. You could even have 3 x SD-Card (only one bootable) or 3 x eMMC (only one bootable).

Please look at STM32MP157F-EV1 for instance which embed SD-Card + eMMC.


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