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MSP430G2553 Global Variable Declaration

Andrew Butler
Expert 2520 points
Other Parts Discussed in Thread: MSP430G2553, MAX232

I am trying to define global variables for a simple PWM code but for some reason, CCS does NOT recognize the "Frequency" and "DutyCycle" variables as global. I have attached my code below. Are you able to determine what is going on?

SpeedSensorTest.zip

Thank you,

Andrew

  • 0
    Guru 303280 points

    What do you mean with "does not recognize"? What specific problem are you seeing?

    (It's likely that these variables got optimized away because they never change.)

  • 0 in reply to Clemens Ladisch
    Expert 2520 points
    I believe CCS thinks those two variables are local because when I try to vary them in the expression window of the debug session, it says "Error: Could not read 0x200: Execution state prevented access".
  • 0 in reply to Andrew Butler
    Guru 303280 points

    Yes, this is what happens when they got optimized away.

    The compiler knows that these variables never get changed by your code.
    If you want to modify them in ways that the compiler does not know about, declare them as volatile.

  • 0 in reply to Clemens Ladisch
    Expert 2520 points
    Thank you for that suggestion but I am still having the same issue. I have copied and pasted my updated main code below. Please let me know if I redefined those variables correctly.

    /*
    * ======== Standard MSP430 includes ========
    */
    #include <msp430.h>

    /*
    * ======== Grace related includes ========
    */
    #include <ti/mcu/msp430/Grace.h>

    volatile unsigned long Frequency = 16000;
    volatile unsigned long prevFrequency = 0;
    volatile unsigned long DutyCycle = 8000;
    volatile unsigned long prevDutyCycle = 0;

    /*
    * ======== main ========
    */
    void main(void)
    {
    Grace_init(); // Activate Grace-generated configuration

    while(1)
    {
    if( prevFrequency != Frequency )
    {
    TA0CCR0 = Frequency; // TA0CCR0, Timer_A Capture/Compare Register 0
    prevFrequency = Frequency;
    }

    if( prevDutyCycle != DutyCycle )
    {
    TA0CCR1 = DutyCycle; // TA0CCR1, Timer_A Capture/Compare Register 1
    prevDutyCycle = DutyCycle;
    }
    }
    }
  • 0 in reply to Andrew Butler
    Guru 303280 points

    Okay, volatile is a bad idea.

    Instead let's pretend to actually change these variables:

    if (WDTCTL == 0) { /* never actually happens */
    Frequency = 0;
    DutyCycle = 0;
}

  • 0 in reply to Clemens Ladisch
    Expert 2520 points
    I never had problems with global variables within CCS before now but I am still having the same problem. I tried two different things: one was pasting that code snippet before the while(1) loop and another time pasting it within the while(1) loop and had no resolution for either situation. I have copied and pasted my main code below.

    /*
    * ======== Standard MSP430 includes ========
    */
    #include <msp430.h>

    /*
    * ======== Grace related includes ========
    */
    #include <ti/mcu/msp430/Grace.h>

    volatile unsigned long Frequency = 16000;
    volatile unsigned long prevFrequency = 0;
    volatile unsigned long DutyCycle = 8000;
    volatile unsigned long prevDutyCycle = 0;

    /*
    * ======== main ========
    */
    void main(void)
    {
    Grace_init(); // Activate Grace-generated configuration

    while(1)
    {
    if (WDTCTL == 0) // never actually happens
    {
    Frequency = 0;
    DutyCycle = 0;
    }

    if( prevFrequency != Frequency )
    {
    TA0CCR0 = Frequency; // TA0CCR0, Timer_A Capture/Compare Register 0
    prevFrequency = Frequency;
    }

    if( prevDutyCycle != DutyCycle )
    {
    TA0CCR1 = DutyCycle; // TA0CCR1, Timer_A Capture/Compare Register 1
    prevDutyCycle = DutyCycle;
    }
    }
    }
  • 0 in reply to Andrew Butler
    Intellectual 775 points

    Replace

    #include<msp430.h>

    with

    #include <msp430g2553.h>

    and check

  • 0 in reply to Andrew Butler
    Guru 74080 points
    Andrew, do you have any optimizations enabled?
  • 0 in reply to Andrew Butler
    Guru 16361 points

    Andrew Butler said:
    I believe CCS thinks those two variables are local because when I try to vary them in the expression window of the debug session, it says "Error: Could not read 0x200: Execution state prevented access".

    Are you trying to modify those globals while the program is actually running (as opposed to when it's paused in the debugger)?

  • 0 in reply to Robert Cowsill
    Guru 74080 points
    Yeah, this won't work :-) Good question!
  • 0 in reply to Dennis Eichmann
    Expert 2520 points

    Yes, I am trying to modify those variables while the program is running because I have been able to do it before. However, my real goal is to attach a GUI to this program and it won't work because it is not recognizing those variables as global.

  • 0 in reply to Andrew Butler
    Guru 74080 points
    Modifying variables or registers is only possible when the program is paused.
  • 0 in reply to Dennis Eichmann
    Expert 2520 points
    So how do I get my GUI to work because it is not recognizing those variables?
  • 0 in reply to Andrew Butler
    Guru 74080 points

    If you pause your program, are you able to modify them now?

  • 0 in reply to Dennis Eichmann
    Expert 2520 points
    And will that work if I run it as a stand alone program with the runtime app?
  • 0 in reply to Andrew Butler
    Guru 74080 points

    Do you plan to establish a connection to the PC where something is running that modifies the PWM of the micro?
    This no problem - the micro can change those variables during runtime, of course.

    But the debugger cannot.

  • 0 in reply to Dennis Eichmann
    Expert 2520 points
    Establish a connection like UART? Is that the only way to get it to work without having to pause the program?
  • 0 in reply to Andrew Butler
    Guru 74080 points

    When using a GUI on the PC, some kind of RS232-UART (MAX232) or USB-UART bridge (FT232) is common. But this variable can be changed from several sources like input buttons, encoders or any other user-interface to act with the running program.

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