• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 99 subscribers
  • Views 254 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Suggestions for reducing power on DM648

Eddie3909
Guru 10385 points

Hi

Our system uses a DM648 at 864 MHz. We are trying to reduce power consumption, but didn't get much (400 mW) when we reduced the clock from 864 MHz (50% utilization) to 594 MHz (88% utilization).

What other things should we try to reduce the watts?

We are using 2 video ports, uart, emif and ddr2.

I have tried setting the unused peripherals (i.e. VLYNQ, SPI, HPI, the 3 unused vports, AMcBSPs....10 perripherals total) to disable state. This reduced power by  about 100 mW. The spread sheet (http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=spraar5a) calculated about 200 mW. Its not near the reduction we need, but its something. Is the spreadsheet incorrect? Should we have got 200 mW?

Thanks

  • 0
    Guru 10385 points

    Hi

    I'm also trying to find out if its possible to sleep the CPU will it waits for a video frame to process. I found this in the DM648 subsystem reference guide

    Additional power saving can be achieved by stopping the clock source to the C64x+ Megamodule by
    programming the power and sleep controller (PSC) to place the C64x+ Megamodule in Disable state.

    When they refer to the C64x Megamodule, do they mean the "DSP module" (#33 of Table 6-1)?

    In the subsystem ref guide, is "C64x+ DSP" synonymous with "C64x Megamodule" and "DSP module"?

    If it is synonymous, then from 7.4.2. DSP module on/off, an external device is needed to complete the program the PSC. True?

    Would it be possible to disable the "DSP module" while the video ports DMA data into SDRAM?

    Is it possible to have the DMA receive UART data and store in SDRAM while the "DSP module" disable?

    Is it even worthwhile to do this? (i.e. will it save much power?)

    Could I execute the IDLE command and let the video port EDMA interrupt wake the CPU (aka DSP module or whatever you guys refer to it as) back up?

    The IDLE command in one task will cause all other tasks to also sleep. Can I assume that they will wakeup in that last state they were in?

    Cheers

  • 0 in reply to Eddie3909
    TI__Expert 3320 points

    Hello Eddie,

    You are taking the right things into account. Disable as many unused peripheral modules as you can and operate the clock at the appropriate frequency. The static (leakage) power on the DM648 is pretty significant so there is only so much you can do. The only way to reduce the leakage power, which is what dominates the power consumption, is to lower the case temperature.  You can explore the effects of adding a heat sink and airflow in the “Heat Sink Calculation” tab of the power spreadsheet.

    A new version of the DM648 power spreadsheet was just uploaded to the web last week that includes more accurate leakage models.
    http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=spraar5b

    Also, the DSP Megamodule is in fact synonymous w/ the “C64x+ DSP” and “DSP Module”. Here’s an app note describing the “Megamodule”: http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=spraa68

    This is also addressed in detail in the subsystem reference guide which you have found – section 2.1:
    http://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=sprueu6b

    It looks like you can not disable/enable the DSP module without the help of an external host. You should be able to study the power consumption spreadsheet to see what this would even buy you.