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Is multiple SD-Cards on one Omega2 possible?

  • Is it possible to connect two SD-Cards to the same SDIO interface?

    From the official OM-O2S / OM-O2SP datasheet version 1.7 it says:
    "There is a single SDIO interface. Only one of eMMC, SD/Micro-SD, or other SDIO device can be
    used. The SDIO interface supports the SDXC specification for SD cards, with a maximum capacity of
    2 TB and a maximum transfer speed of 300 MB/s, and the eMMC5.1 interface for eMMC storage."

    And from the reference scematic https://github.com/OnionIoT/Omega2/blob/master/Schematics/Omega2S-Reference-Schematic.pdf it says:
    "The Omega2S can only support one SDIO Device. If you are connecting to a Micro-SD card, then do not connect to EMMC memory."

    I get that when using an EMMC standard device, I wont be able to use a SDXC device, since they use two different specifications. But I am wondering if I connect two devices both using SDXC in parallel, will the Onion Omega2 be able to correctly talk to both of them?
    From an old post https://www.embeddedrelated.com/showthread/comp.arch.embedded/69909-1.php, a person explains that it could work on MMC.

    If it turns out, to not be possible, will I be able to connect the SD-Cards over SPI?

  • If anyone is reading this, after further research it seems like I have 3 ways of connecting SD cards directly.

    1. Connecting the SD-card directly using the SDIO interface on pins 22-29
    2. Connecting the SD-card directly over the unused SPI-bus CS1 (not SPI CS0) on pins 6-8
    3. Installing software https://openwrt.org/docs/guide-user/hardware/mmc_over_gpio and using unused GPIOs to connect additional SD-cards.

    It doesn't seem to be practical to connect two SD-cards to the same SDIO interface as it would require multiplexing the bus (at least the select signal), but if anyone knows how it could be done, I would still be interested. My main concern is, that the operating system wouldn't be able to automatically detect the SD-cards and differentiate them correctly, but I may be wrong and they might have unique ID's.

  • @Jens-Modvig I'm watching with interest.

  • @crispyoz at the moment I am planning on testing option 1 with multiple SD-cards on the SDIO interface and option 2 with one SD-card. I will update the post, once I have gotten some results.

  • @Jens-Modvig I wonder if the driver can differentiate between the two devices as the spec requires, but I believe SDIO will allow 3 on the same CS line.

    I'm very interested see your results.

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