MSP-EXP432E401Y: System hanged at the location SysTickValueGet() called

HaeSeung Park

Part Number: MSP-EXP432E401Y

Hi,

I am writing delay/sleep routine with SysTick driverlib APIs without interrupt in MSP-EXP432E401Y as follows:

    hz4milliseconds = ui32SysClock / 1000;
    
    SysTickEnable();                        // no interrupt
    SysTickIntDisable();

    while (1) {
        sleeptime = 1000;                   // 1 second
        for ( ; sleeptime > 0 ; --sleeptime) {
            SysTickPeriodSet(hz4milliseconds);
            while (SysTickValueGet() & hz4milliseconds > 0) ;
            // while (SysTickValueGet() > 0) ;
        }

        GPIO_toggle(CONFIG_GPIO_LED_0);
    }

I would like to make LED toggling every 1 second, but execution hanged at SysTickValueGet().

Please advise me how to solve this problem.

Any help/tips are appreciated in advance.

HaeSeung

over 3 years ago

0 Bruce McKenney over 3 years ago

Guru 100885 points

> while (SysTickValueGet() & hz4milliseconds > 0) ;

I'm not completely sure what you intended, but maybe you meant "-" instead of "&"? Even with this change, this is unlikely to work since there will only be one CPU cycle (too short to see) where the condition is false (note: arithmetic will be unsigned).

I suggest instead something like:

> SysTickPeriodSet(0xFFFFFF+1); // Full range, once and forever

> SysTickEnable(); // Once and forever

then in the loop:

> uint32_t start = SysTickValueGet();

> while (((start-SysTickValueGet()) & 0xFFFFFF) < hz4milliseconds) /*EMPTY*/; // Watch down-counter difference (24 bits)

The unsigned (24-bit) arithmetic will deal with timer wrap up to (16M/120MHz)= ~139msec.

[Edit: This is untested, but I think it's about right.]

0 Charles Tsai over 3 years ago

TI__Guru**** 191906 points

Hi,

Systick counter is only 24-bit wide and will not give you a 1 second period but rather a maximum of ~139ms as explained by Bruce. I will suggest you use the general purpose timer in 32bit mode to achieve the 1 second timeout. There is an example for it at C:\ti\simplelink_msp432e4_sdk_4_20_00_12\examples\nortos\MSP_EXP432E401Y\driverlib\gpt_32bit_periodicmode_interrupt. In this example. the LED is toggled every 1 second.

+1 HaeSeung Park over 3 years ago

Intellectual 355 points

Dear Bruce and Charles,

Your tips are very helpful to solve this problem. Final code as follows:

    volatile uint32_t elapsedTime;
    uint32_t          startTime;

    hz4milliseconds = ui32SysClock / 1000;	// period for 1 milli second

    SysTickEnable();                        // enable module
    SysTickIntDisable();					// no interrupt
    SysTickPeriodSet(hz4milliseconds);

    while (1) {
        sleeptime = 1000;                   // 1 second
        for ( ; sleeptime > 0 ; --sleeptime) {
            // repeatedly evaluate elapsed time till 1 milli sec
            startTime = SysTickValueGet();
            do {
                elapsedTime = (startTime - SysTickValueGet()) & 0x00FFFFFF;
            }
            while(elapsedTime <= hz4milliseconds);
        }

        GPIO_toggle(CONFIG_GPIO_LED_0);
    }

Thanks, both of you.

HaeSeung

0 Bruce McKenney over 3 years ago in reply to HaeSeung Park

Guru 100885 points

I hesitate to argue with success, but I'm concerned this code may get you in trouble someday.

Skipping to the end:

> SysTickPeriodSet(hz4milliseconds);

I (still) recommend instead:

> SysTickPeriodSet(0xFFFFFF+1); // Full range, once and forever

---------

This code is doing modulo-16M (24-bit) arithmetic on a modulo-120K value. This will work-by-accident most of the time, since each time the timer wraps (through 0) the modulo-16M difference will appear as a large (unsigned) value, so the loop will exit.

But there are corner cases. Existence proof: Since the startTime is being fetched at some (unknown) point in the cycle, it is possible it will fetch the value (120000-1). When the counter counts to 0, the difference will be (120000-1), and when the counter wraps back to (120000-1) the difference will go back to 0; as a result, the loop will never exit. The "failure band" is actually much larger than this, since the code in the loop will add many CPU clocks of uncertainty.

Doing modulo-120K arithmetic (besides being extra trouble) won't help, since then the difference will never exceed the modulus. The solution is to use a modulus (SysTick period) much larger than your timing period (1ms), and modulo-16M (~139ms) is very convenient for your arithmetic.

0 HaeSeung Park over 3 years ago in reply to Bruce McKenney

Intellectual 355 points

I fixed my code as recommended.

Thanks a lot, Bruce.

HaeSeung

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MSP-EXP432E401Y: System hanged at the location SysTickValueGet() called