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CCS/TMS320F28379D: PWM Frequency always half

Guilherme Fuzato
Prodigy 70 points

Part Number: TMS320F28379D
Other Parts Discussed in Thread: LAUNCHXL-F28379D, CONTROLSUITE

Tool/software: Code Composer Studio

I'm testing the LAUNCHXL-F28379D by using the example projects provided by texas instruments, the problem is that the  PWM frequency is always half of the examples.. I have tried many examples in the controlsuite and also the examples provided in "http://processors.wiki.ti.com/index.php/C2000_One-Day_Workshop". The last one I tried in the the workshop "http://processors.wiki.ti.com/index.php/C2000_One-Day_Workshop" with the project named "Lab3_cpu01" was supposed to present a 2kHz PWM output... However, when measuring with the oscilloscope the output frequency is 1kHz... 

I just bought this board and I'm wondering if the board is somehow deffective... 

Can anyone please help me?

  • 0
    TI__Guru** 116091 points

    Hi,

    Two points to note -

    1. On this device PWM runs 1/2 of SYSCLK frq unlike earlier devices where PWM used to run at SYSCLK.
    2. On launchpad the external crystal is 10MHz instead of 20MHz hence the SYSCLK frq may be 1/2 of what example is expecting. In that case you need to change the PLL multiplier.

    Regards,

    Vivek Singh

  • 0
    TI__Genius 17315 points
    Guilherme,

    In your project Properties, please check the configuration of the predefined symbols. Under “C2000 Compiler” select “Advanced Options” and then “Predefined Symbols”. In the predefined name box (“Pre-define NAME”) see if the “Enter Value” window has CPU1 and _LAUNCHXL_F28379D (note leading underscore). These names are used in the project to conditionally include the peripheral register header files code specific to CPU1 and the LaunchPad.

    Specifically, this does a software correction for the external crystal that is used on the F28379D LaunchPad:

    #ifdef _LAUNCHXL_F28379D
    InitSysPll(XTAL_OSC,IMULT_40,FMULT_0,PLLCLK_BY_2);
    #else
    InitSysPll(XTAL_OSC, IMULT_20, FMULT_0, PLLCLK_BY_2);

    Also, please try loading the solution for Lab 7 in the following workshop:

    processors.wiki.ti.com/.../C2000_Multi-Day_Workshop

    In this workshop, the internal 10 MHz oscillator is used, so no correction is needed. Run this lab exercise and measure the PWM waveform. It should be 2 kHz.

    I hope this helps. If this answers your question, please click the green "Verified Answer" button. Thanks.

    - Ken
  • 0 in reply to Ken Schachter
    Prodigy 70 points

    Ken,

    I configured the "Predefined Symbols" asyou mentioned before... I also noticed that when the command "InitSysPll(XTAL_OSC, IMULT_20, FMULT_0, PLLCLK_BY_2);" is used the PWM frequency is 1/4 from expected, while when the command "InitSysPll(XTAL_OSC, IMULT_40, FMULT_0, PLLCLK_BY_2);" is used the PWM frequency is 1/2 from the expected value.. 

    I'm trying to run the Lab7 that you mentioned but it seems that there are many empty configurations in the PWM initialization code...

  • 0 in reply to Vivek Singh
    Prodigy 70 points
    Vivek, as Ken mentioned, the "F2837xD_SysCtrl.c", which is included in the examples should be able to correct this problem since the command InitSysPll(XTAL_OSC,IMULT_40,FMULT_0,PLLCLK_BY_2); is equal to 200Mhz = 10Mhz (XTAL_OSC)* [40 (IMULT_40)+ 0 (FMULT_0)]/ 2 (PLLCLK_BY_2)
    Right?


    #ifdef _LAUNCHXL_F28379D
    InitSysPll(XTAL_OSC,IMULT_40,FMULT_0,PLLCLK_BY_2);
    #else
    InitSysPll(XTAL_OSC, IMULT_20, FMULT_0, PLLCLK_BY_2);
  • 0 in reply to Guilherme Fuzato
    TI__Genius 17315 points
    Guilherme,

    From you post:

    I'm trying to run the Lab7 that you mentioned but it seems that there are many empty configurations in the PWM initialization code...

    That is why I told you to run the solution code. You will find this in the solutions folder.

    - Ken
  • 0 in reply to Ken Schachter
    Prodigy 70 points

    Ok!

    I found the problem.. 

    the ClkCfgRegs.PERCLKDIVSEL.bit.EPWMCLKDIV must be zero, otherwise the output frequency will be divided by 2. 

    Thank you Ken! 

  • 0 in reply to Guilherme Fuzato
    TI__Guru** 116091 points
    Hi,

    Please note that max frq supported for PWM on this device is 100MHz (please refer Table 5-12. Internal Clock Frequencies of device maual) so if you are running the SYSCLK at 200MHz then you have to set this divider to divide by 2.

    Regards,

    Vivek Singh
  • 0 in reply to Guilherme Fuzato
    TI__Genius 17315 points
    Guilherme,

    I am glad that you found the problem. Just for reference, from my workshop lab file:

    // Configure the prescaler to the ePWM modules. Max ePWM input clock is 100 MHz.
    ClkCfgRegs.PERCLKDIVSEL.bit.EPWMCLKDIV = 1; // EPWMCLK divider from PLLSYSCLK. 0=/1, 1=/2

    We are running the device at 200 MHz and the above structure is set to 1 for this reason. Your setting will depend on you PLLSYSCLK value (see module 5).

    - Ken
  • 0 in reply to Ken Schachter
    Prodigy 70 points
    Thanks for your attention Ken!

    Guilherme.