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Can TMS320C6455 use more than 512MB DDR? Can DDR2 DIMM be used with C6455?

Smokensparks
Intellectual 440 points
Other Parts Discussed in Thread: TMS320C6455

Hi,

My customer has the following questions regarding TMS320C6455 DDR capacity and type: 

1.       The C6455 DSP states that the DDR2 interface has a limitation of 512 MB of address space.  Do you know if this space can be "paged"?  In other words, are we able to hang more than 512 MB off of this bus and effectively be able to read/write to it?  512 MB seems like a fairly small amount considering the size of available DDR2 memory devices.

2.       Can a DDR2 DIMM be used with this device?  It would seem unusual to have a DDR2 interface without the capability of supporting the large selection of DIMMs in the industry.

Thanks,

Rick

  • 0
    TI__Guru* 84110 points

    The C6455 supports only the address range of 512MB for DDR2 space.

    In the days before DRAM, we used to do a lot of paging to get larger available space for Flash memory and SRAM, and those are still reasonable. Some older devices with early DRAM/SDRAM support might still be able to survive external logic to page devices in/out. But the newer SDRAM and especially DDR2 controller logic (even though the C6455 is a few years old) expect the memory environment to look a certain way and cannot be expected to support a new topology like externally-paged DDR2. Consider refresh and DDR2 internal-paging as two features that the DDR2 controller dictates tight control over - these would be invalidated by an invisible external paging scheme.

    From what I can tell, a DIMM puts out 64 bits of data at a 1/2 clock rate. You would have to go to a DDR2-1066 / PC2-8500 to get the rate required and then through out half of the data. This would not be a good cost proposition, I would expect. But the bigger problem is that there would be no way to meet the layout requirements that TI requires for the C6455 to interface with DDR2-533 devices.

     

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  • 0
    TI__Guru*** 125430 points

    Sounds like you're a PC-guy, Rick!  ;)  The embedded processing world is much different -- welcome!

    Rick Rubio said:
    The C6455 DSP states that the DDR2 interface has a limitation of 512 MB of address space. 

    Limitation?  I suppose it depends on what you're doing, but all of my customers that have used this device have hooked up either 128 MB or 256 MB.  I've not even seen anyone hook up the full 512MB of DDR2 (though I imagine someone probably is).

    Rick Rubio said:
    It would seem unusual to have a DDR2 interface without the capability of supporting the large selection of DIMMs in the industry.

    What's unusual about not requiring our customers to purchase 200-pin DIMMs?  Size, power, and cost are often critical to our customer base.