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Question About Selecting Microprocessor

Martin Risso
Intellectual 470 points
Other Parts Discussed in Thread: CSD, CC3200, MSP430FR5994

Hi,

I'm trying to find a low power Cortex that has an MMC / eMMC / SD port that supports the SD 3.0 specification. I have found many that support the SD 2.0 specification. The difference is that the SD 2.0 specification works with SD and SDHC memory cards. The SD 3.0 specification works with SD, SDHC and SDXC memory cards.

Although I don't need the capacity of SDXC, my marketing people do not want users confused because they used an SDXC card and it doesn't work.

  • 0
    TI__Mastermind 49692 points

    Hi Martin,

    The MSP430FR5994 LaunchPad has a microSD card port, although this device is not ARM-based. See Section 2.2.5.1 in the User's Guide for more details.

    Also, I've seen where the ARM-based MSP432 has been used with an SD card. While the link below is not supported by TI, this software was allegedly tested on a 32MB card and should be a good reference.

    After reading a little about the differences between SD 2.0 and SD 3.0, there seems to be two key changes (ignoring larger capacity and higher speed):

    • "The format of the Card-Specific Data (CSD) register changed between version 1 (SDSC) and version 2.0 (which defines SDHC and SDXC)", found on Wikipedia here
    • "The file system used on the MMC/SDC is FAT. The MMC/SDC specifications define the FAT type as: FAT12 for 64MB and smaller, FAT16 for 128MB to 2GB, FAT32 for 4GB to 32GB and exFAT for 64GB to 2TB", found here

    Assuming these changes are implemented in software correctly, this may work. However, I'd recommend spending more time researching these differences. Here are some additional resources on the MSP430 side that should be helpful.

    Regards,

    James

    MSP Customer Applications

  • 0 in reply to James Evans
    Intellectual 470 points
    Hi James,

    Some of the never SDHC and SDXC cards specifically state that they do not support SPI interface. This is why I'm looking for a microprocessor that will work with the newer cards.
  • 0 in reply to Martin Risso
    Genius 5505 points

    Hi Martin,

    Look at CC3200. It has specific SD card v.2 host controller with 1-bit data transfer and 1024 byte data buffer. The CC3200 has 240 MHz speculated bus clock, but its card interface support clocks up to 24 MHz. So, you will not get data transfers more than 3 MB/s. If you plan implementation of ex-FAT file system (to handle big files) on SDXC, you should know that this protocol is Microsoft proprietary with obligatory licensing fees. Otherwise you'll have to deal with no more than 4GB file sizes and 32GB of flash card memory capacity.

    Rising clock speed means rising power consumption of the device. MSP devices developed with a specific constrain - to limit power consumption to lowest levels possible. That's why they do not use high-speed clocks. There are other practical reasons about clock limitation.

    MSP430FR5994 is a good device. You will get maximum speed transfer on SD card by SPI communication up to 16Mbit/s (in both directions simultaneously), another words, up to 2MB/s data transfer (including protocol data).

    It's up to you to choose what is more important to you: power consumption, other constrains or high performance. You can even choose something based on ARM-Cortex-A platform with 1GHz or higher clock rates.

    Alexey

  • 0 in reply to Alexey Bagaev
    Genius 5505 points

    I forgot to add: if you want to implement saving a file to FAT32 with naming more than 8.3 symbols on a custom device, you have to deal with Microsoft patents and pay them fees or penalties for such inadmissible actions. :)

  • 0 in reply to Alexey Bagaev
    Intellectual 470 points

    Hi Alexey,

    From my reading of the SD card specifications, I think I need a host interface with a 3.0, not 2.0 SD card specification to work with SDXC cards, even if I implement exFAT. I don't need super fast transfer speeds. I simply need it to work if the end user uses an SDXC card instead of an SDHC card. I think the off the shelf SDXC cards will already be exFAT formatted. My marketing people do not want end users disappointed because they bought the wrong SD card.

    But it seems that there are reasons that the physical aspects of SD 3.0 are not implemented in low power microprocessors. This is actually what I am trying to verify.

    Marty

  • 0 in reply to Martin Risso
    Genius 5505 points

    Martin,

    What specific 'physical aspects of SD 3.0' are you talking about? - Voltage levels are in the range. Connectors are the same.
    Yes, SDXC cards definitely preformatted with exFAT. For such type of support contact representatives from Microsoft or TI directly. It needs special business agreement, probably even under NDA. I cannot help you with that.

    Alexey

  • 0 in reply to Martin Risso
    Genius 5505 points
    I can confirm that SPI mode (3.3 V by default) is marked as a mandatory support for all types of SD card devices, including latest HDXC. As even such type of information is marked as "confidential", any additional info you should better find yourself.
  • 0 in reply to Alexey Bagaev
    Intellectual 470 points

    Hi Alexey,

    The following is from page 113 , section 7.1 of  "Physical Layer Simplified Specification Version 3.01" from the SD Group and SD Card Association:

    "The commands and functions in SD mode defined after the Version 2.00 are not supported in SPI
    mode. The card may respond to the commands and functions even if the card is in SPI mode but host
    should not use them in SPI mode."

    I interpret this as some SDXC cards might work in SPI mode but there is no guarantee that all SDXC cards will work in SPI mode. 

    I  don't get a "warm and fuzzy" feeling that I can guarantee that there won't be angry customers because they bought the "latest and greatest" SDXC card and it doesn't work in the product. I have looked at some of the newest eMMC giant flash chips and they specifically say they do not support SPI mode. (I'll attach a data sheet if you want). My guess is that the latest "huge" eMMC flash chips are designed to go into an SD card and the SD card simply brings the chip pins out to connector pins, single chip SD card.

    Marty

    www.linkedin.com/pub/martin-risso/71/599/a09

  • 0 in reply to Martin Risso
    Genius 5505 points

    Basic commands are supported by spec V3.x. This means that all commands from spec V2.0 are supported in SDXC SPI mode, but commands from spec V3.01 are not. So SPI mode is backward compatible.
    Look at the Table 3-10 from the document you've mentioned.

    Alexey

  • 0 in reply to Martin Risso
    Genius 5505 points

    If MSP design does not fit your requirements, you can switch to TMS320C5545. It has 4-pin SD mode at 50 MHz.

  • 0 in reply to Alexey Bagaev
    Genius 5505 points

    Implementing complex peripherals for MSP needs additional ticks to function. MSP430 devices do all these as low as 1 tick. Rising peripheral bus clocks to fit such demands means rising overall power consumption of MCU with needs of more powerful supply chain, which has higher quiescent current. MSP team will not go to this direction. There are plenty of other products in other functional range.

  • 0 in reply to Martin Risso
    Genius 5505 points

    Martin Risso said:
    I have looked at some of the newest eMMC giant flash chips and they specifically say they do not support SPI mode.

    Marty,

    If you are talking about support in your devices of such type of non-SD-certified flash cards like this one:

    ...I would say, you will not get access to it even through 1.8V 4-pin SD-mode. So, even the C5545 is not a choice for such type of 'flash memory' cards.

    Alexey

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