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TMS320C6424 and spansion flash larger than 32 mb with EMIF

Johan Westlund
Prodigy 110 points
Other Parts Discussed in Thread: TMS320C6424

I seem to be finding conflicting information on if its possible to use the EMIF of TMS320C6424 with S29GL512 ( a 64 mb spansion flash). Doing so requires more than the standard 24 adress lines. Im assuming that this means using one of the chip select pins (i.e. EM_CS2) but it seems to me that the correct way of doing this is largely undocumented. 

We use an old code example for the evaluation module from spectrum digital as the driver for the 32 mb version we have today. That file seems to have definitions for the 64 mb version as well so it seems like its possible to use a 64 mb flash seamlessly. Is that true? Are there any downsides or cave ats? 

  • 0
    TI__Mastermind 35645 points

    Hi,

    Thanks for your post.

    Typically yes, the device should support up to 128 Mb (mega bit)  but please ensure it on the hardware side too.

    We will investiage more on this and will get back to you shortly.

    Thanks & regards,

    Sivaraj K

  • 0 in reply to Sivaraj Kuppuraj
    Prodigy 110 points

    Support up to 128 megabyte you mean? 128 Mbit is only 16 megabyte which is lower than what we use today...

    Thanks for your support on this.

  • 0 in reply to Johan Westlund
    Prodigy 60 points

    Hi, 

    From reading the TMS320C6424 spec, it seems the EMIF supports up to 128MB with 4 chip selects, i.e. 32MB per chip select. 

    If you use a x16 bit Flash, 32MB will use 24 address lines. That matches what EMIF has. 

    So I think you were right at your original post. You have to use 2 chip selects to fully access the Spansion 512Mb device. 

    Best regards,

    Zhi Feng
    Senior Member of Technical Staff
    Customer Engineering

    EcoSystem Marketing
    Spansion Inc.

    office:     +1 512 934 5735

    email:      zhi.feng@spansion.com

  • 0 in reply to Zhi Feng
    Prodigy 110 points

    Yes, that is what I assumed. The trouble is that I can not redesign a complete circuit board based on assumptions. I need to know if the EMIF interface supports this natively or if there might be any issues with this approach.  

    From the drivers we use for flash memory access today I can not see any reference to any special treatment for S29GL512, it simple treats it just like S29GL256 with a larger adress space. That means that the EMIF seems to support this natively. But since theres no documentation that specifically says what pin to use it would be a guess  from my part that it is possible to use EM_CS2. Its probably true but theres no guarantee since it is undocumented (from what I can tell).

  • 0 in reply to Johan Westlund
    Prodigy 110 points

    The problem is that the memory needs a chip select in addition to the extra adress line. This chip select shall be active regardless of what part of memory is being accessed. That is a different behaviour from when you have several memory chips with their own unique chip selects. So if this is possible it means either that you need external logic or there needs to a way to configure EMIF for this.

  • 0 in reply to Johan Westlund
    TI__Mastermind 43660 points

    Hello Johan,

    The C6424 device supports 32MB EMIF asynchronous address space per CS and maximum of 128MB with all 4 CS.

    If you want to access single 64MB NOR flash, you need to have 2 CS and one additional address line. The GPIO can be used for additional address line. Further you need to do OR logic of 2 CS from the EMIF controller and connect it to the NOR flash CS.

    To implement this you need to modify the driver accordingly to support this design. Also you need to take care of the timing constraints as well.

    Since this application requirement exceeds the device limitation (32MB per CS), I am not  sure TI does have any documentation or application note. The above suggested design shall be implemented with designer's own risk.

    Regards,

    Senthil

  • 0 in reply to Johan Westlund
    Prodigy 110 points

    Is there any reason not to use the most significant chip select as adress line? 

    EM_CS2 or EM_ CS3 ->flash chip select

    EM_CS3 -> flash A24 (most significant adress bit)

  • 0 in reply to Johan Westlund
    TI__Mastermind 43660 points

    Hello Johan,

    As explained in the above post, you need to have 2 CS signals to access 64MB NOR flash.

    Yes, you can use EM_CS2 and EM_CS3 (with OR logic) for flash chip select and EM_CS3 for flash A24. But you need to ensure the drive strength of CS3 signal to drive both flash CS and A24.

    Regards,

    Senthil