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C5535 Idle Mode 3

Nicolas Deup
Intellectual 590 points
Hi, Is it possible for the C5535 CPU set in Idel Mode 3 (running on the 32.768 KHz quartz) to toggle GPIO ? The target is the following. My DSP has to run using an external 12 MHz oscillator. When the device togle from running mode to its low power mode ( IDLE3 mode), the last thing I want to do is to use a GPIO to set the 12 MHz oscilator Enable Pin in Low power mode. At this stage, the DSP should perhaps have enough time to toggle from running mode to IDLE3 Mode. If not, I will have to add an external delay (using some IC/HW) from the time the DSP set the 12 MHz oscillator Enable Pin Now, I have to be sure that the DSP can toggles from IDLE3 mode (on 32.768 crystal), to Running mode (using PLL and 12 MHz oscillator). So my goal is for the CPU to toggle the GPIO pin to enable the 12 MHz oscillator, wait a while for the oscillator to get its steady state, and the toggle the CPU from IDLE3 mode to running mode. Any comments about this ? I already have a demo that toggles the CPU from running mode (12 MHz oscillator) to IDLE3 mode (32.768 crystal) and vice versa. What I need now is a way to save power by puting the oscillator in sleep mode and be able to wake up the oscillator. Thanks. Nicolas
  • 0
    TI__Genius 12575 points

    Hi,

    Yes as you have observed C5535 supports Idle3 mode.

    As I understand, you are using GPIO to enable the external 12 Mhz clock before you go to Idle3 mode and use the same GPIO to wake this back. Are you waking up through GPIO interrupt ? This will work, but since the clocks are quite slow there might be quite an amount of latency involved when you enter and exit sleep mode.

    Regards

     Vasanth

     

     

  • 0 in reply to Vasantha K
    Intellectual 590 points
    Vasanth, This is more the opposite. When C55 is in active mode (using the 12 MHz oscillator), I use a GPIO to disable the oscillator as the last instruction and then set the CPU in IDLE3 mode : I have to be sure that the 12 MHz oscilltor is still ON for the last DSP instructions before it really get in IDLE3 mode When C55 is in IDLE3 mode (using the 32.768 KHz), I use the same GPIO to enable the oscillator as the first instruction. I have to be sure that the 12 MHz oscillator is ready before the PLL really needs the 12 MHz signal to lock. I can use either INT1 or WakeUp pin (otherwise RTC alarm) to wake up the DSP. What about I2C peripherical when DSP in IDLE3 mode ? thanks Nicolas
  • 0 in reply to Nicolas Deup
    TI__Genius 12575 points

    Nicolas, 

    With respect to GPIO operations it sounds ok to me. 

    Your question on I2C  - as mentioned in the technical reference module -  "Idle the desired peripherals in the peripheral clock domain by modifying the peripheral clock gating configuration registers (PCGCR1 and PCGCR2)" -  So need not clock gate I2C. And with respect to wake up it can be woken up by any unmasked peripheral interrupt as defined in IER0 and IER1 or  wakeup pin or RTC interrupt or External hardware interrupt. 

    Hope this helps. 

    Regards

     Vasanth