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Linux/AM3352: eMMC JEDEC questions

Mihir Gupta65
Intellectual 2155 points
Part Number: AM3352


Tool/software: Linux

Hi Team,

I have a customer who has a few questions about the MMC interface of the AM3352. Question is below:

We use your Sitara CPU (AM3352BZCZD80, AM3352BZCZD30). The eMMC Flash parts that we used at that time are slowly being discontinued. 

Can you tell me:
1. Which JEDEC standard is supported by the HW of the CPU (4.41, 4.5, 5.0?)
2. Which JEDEC standard is supported by the Linux driver? Was there any change in the past? The question is that some of our customers are using an old Linux kernel (3.x), would new eMMC building blocks also work?
3. Did you internally do a compatibility test with the CPU and eMMC devices from different manufacturers? Do we have any results that we could share?
4. Any suggestions from TI how to deal with the discontinuations of eMMC flash?

Regards
Mihir
  • 0
    TI__Guru**** 393215 points
    Hi,

    1. eMMC v4.41 specification.
    2. JEDEC specification has no relation to the Linux driver.
    3. This is not available publicly.
    4. v5.0 parts are backward compatible to v4.41.
  • 0
    Prodigy 70 points
    Hi,

    thanks for the quick reply.
    We have no somehow contradicting answers with regards to compatibility. One of our eMMC supplier said, 5.0 is only backward compatible to 4.5 not 4.41. In addition 5.0 has also a different pinout (additional VSS pins and an addtional DS pin). We also tried a 5.0 eMMC flash in our existing platform and it was not recognised by the CPU. Any hints?

    The linux question came from the fact that in early version of the linux emmc_driver the 5.0 mode is not supported, therefore I thought compatibilty issues could have been caused by this...

    Regards
    Stefan
  • 0 in reply to Stefan Baumann
    TI__Guru 63245 points

    eMMC devices which are compliant to newer versions of the standard should be backwards compatible to the original standard.

     

    Version 4.1 was the first version of the eMMC standard. It was derived from the MMCA System Specification version 4.1. Pin number references and form factor references were removed. Therefore, the pin assignment and PCB footprint of an eMMC device is not defined by the standard. You may be forced to redesign your PCB if you cannot find a pin-compatible replacement.

     

    Outside of potential pin-assignment and form factor differences, I’m not aware of backwards compatibility issues when replacing 4.1 devices with 5.0 devices. Are you being told this from a memory manufacturer or from a distributor? If you have more details, please share this information.

     

    I’m not sure how you connected a 5.0 device that is not pin-compatible to your PCB, but signal integrity is very important.

     

    Our Linux driver is always evolving to support new devices/capabilities. Each updated is tested with the various TI hardware platforms before being released. In some cases it may be necessary to limit capabilities based on hardware components in the system. This is done by defining the limitation in the device tree file which represents capabilities of the hardware platform. I’m not a software expert so not able to help with software specific questions. However, I will ask our eMMC driver expert if he is aware of any backward compatibility issues going from 4.1 to 5.0.

     

    Regards,

    Paul

  • 0 in reply to peaves
    Prodigy 70 points
    Hi Paul,

    thanks for the detailed answers. We dug into this in the meantime and have now also information from another emmc supplier that 5.0 is backward compatible to 4.41. Even that footprint change (additional VSS pins and the DS pin) should not cause any issues. However we already tested a 5.0 device in our existing platform and it was not recognised by the CPU/SW. So it would be helpful if you could ask your driver expert:
    1. Is an old linux version (3.x) with no awareness of emmc 5.0 able to handle new 5.0 emmc devices? Have you tested this?
    2. If no, which linux driver version adds support those 5.0 devices?

    Best regards,
    Stefan
  • 0 in reply to Stefan Baumann
    TI__Guru 63245 points

    I sent your questions to our eMMC driver expert and received the following reply.

    Its the other way around. If MMC was supported in 3.x kernel then newer devices will be compatible with the old standard. We have never tested this though.

    Regards,
    Paul