Shared/multiplexed storage media with i.MX8M Mini

[craigeasdale]

Hello,

I have a situation where I must access storage media from another system, which is also being written to constantly. I was thinking about using SDIO for this, but there is only one of these peripherals on each system. For this reason it makes sense to multiplex two identical SD/eMMC devices and switch them out quickly to allow the the i.MX8M system to copy a chunk of data from one device, while the other writes the next chunk of data to the other.

However, I need to understand what the limitations of the i.MX8M Mini to determine if this will work.

1. What determines the SD card powering/mounting process?
2. Can how SD cards are powered up/mounted be changed?
3. Can the speed of SDIO be changed?
4. Can I use SPI to access SD card data?

If anyone has another suggested approach for this problem I'd also be interested to hear it.

[igorpadykov]

Hi Craig

>1.What determines the SD card powering/mounting process?
>2.Can how SD cards are powered up/mounted be changed?

seems only limitation on such configuration is power-up sequence described in

sect.3.2.1 Power-up sequence  i.MX 8M Mini Applications Processor Datasheet for Consumer Products

>3.Can the speed of SDIO be changed?

I am afraid not, as speed is defined automatically in SD driver when it reads SD capability register.

>4.Can I use SPI to access SD card data?

no.

Best regards
igor

[craigeasdale]

Hi Igor, thanks for your reply.

In table 30 of this document it talks about low speed/full speed/high speed mode (400KHz/25MHz/50MHz). What determines which clock frequency is used? And what is the default/max SDIO clock frequency?

Thanks,
Craig

[igorpadykov]

>What determines which clock frequency is used? 

driver reads CSD register of SD card and sets frequency accordingly.

Details can be found in SD specification on

https://www.sdcard.org/downloads/pls/

Best regards
igor