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MSP430: Can't Single Step Target Program: Could not single step device At the end of ISR

Luqman
Intellectual 320 points
Other Parts Discussed in Thread: MSP430F2274

I have a very basic code. Just blink the LED at the interrupt on any GPIO. 

Issue is I am not able to debug the code. All works fine when it reached at the last curly braces of closing ISR it does not go back and on pressing 'step into' t gives this error. 

MSP430: Can't Single Step Target Program: Could not single step device.

here is code 

#include <msp430.h>

int main(void)
{
WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer
P1DIR |= BIT0; // Set P1.0 to output direction
P1REN |= BIT4; // Enable P1.4 internal resistance
P1OUT |= BIT4; // Set P1.4 as pull-Up resistance
P1IES |= BIT4; // P1.4 Hi/Lo edge
P1IFG &= ~BIT4; // P1.4 IFG cleared
P1IE |= BIT4; // P1.4 interrupt enabled

__bis_SR_register(LPM4_bits + GIE); // Enter LPM4 w/interrupt

}

// Port 1 interrupt service routine

#pragma vector=PORT1_VECTOR
__interrupt void Port_1(void)
{
P1OUT ^= BIT0; // P1.0 = toggle
P1IFG &= ~BIT4; // P1.4 IFG cleared
}

  • 0
    Guru 23000 points

    At the end of the ISR, after ‘P1IFG …’ there is nothing to ‘step’ anymore. The MCU goes into LPM4 (Low Power Mode without a program clock) as defined in ‘main’ and waits until the next interrupt.

  • 0 in reply to Leo Bosch
    Intellectual 320 points
    I want to change Power Mode in ISR. In real, that I understood is that, after executing ISR control goes back to main program and in same Power Mode from which control came before executing ISR(loads the SR value from Stack). I want to change Power Mode in ISR and want to see either it changes or not when control goes back. Here is the same code with just at the : "__bis_SR_register_on_exit(LPMx_bits );" command

    here is code

    #include <msp430.h>

    int main(void)
    {
    WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer
    P1DIR |= BIT0; // Set P1.0 to output direction
    P1REN |= BIT4; // Enable P1.4 internal resistance
    P1OUT |= BIT4; // Set P1.4 as pull-Up resistance
    P1IES |= BIT4; // P1.4 Hi/Lo edge
    P1IFG &= ~BIT4; // P1.4 IFG cleared
    P1IE |= BIT4; // P1.4 interrupt enabled

    __bis_SR_register(LPM4_bits + GIE); // Enter LPM4 w/interrupt

    }

    // Port 1 interrupt service routine

    #pragma vector=PORT1_VECTOR
    __interrupt void Port_1(void)
    {
    P1OUT ^= BIT0; // P1.0 = toggle
    P1IFG &= ~BIT4; // P1.4 IFG cleared

    __bis_SR_register_on_exit(LPM2_bits );
    }
  • 0 in reply to Leo Bosch
    Intellectual 320 points
    One more thing. During debug session of MSP430F2274 control goes back as normal. But in F5529 does not.
  • 0 in reply to Luqman
    Guru 23000 points

    Luqman said:
    __bis_SR_register_on_exit(LPM2_bits );

    There is a little difference: ‘__biS_SR_register()’ Set the bits and ‘__biC_SR_register_on_exit()’ Clears the bits and ‘on_exit’ means not now but when call is completely finished.

    When the LPM is canceled the clock will continue clocking and the program resumes from where it was stopped. Look carefully what will happen in your ‘main’ now.

  • 0 in reply to Leo Bosch
    Intellectual 320 points

    Yes you are right.
    But I know the difference but I am using "__biS_SR_register_on_exit(LPM2_bits );" not "__biC_SR_register_on_exit(LPM2_bits );"

    want when it goes back in main it goes in different mode. Specfiically in my code, It will come from LPM4 and it should go after completing call in LPM2. Am I right ?
    But in debug session control does not go back in the man finishes in the last curly brace,,
    Whereas it goes in case of MSP430F2274 Case f I run same code on it. 

  • 0 in reply to Luqman
    Guru 23000 points
    This is not the common way and not advisable, only ‘main’ should alter the power mode but anyhow, what you do here is setting the bits required for LMP2 but the bits for LPM4 remains set.
  • 0 in reply to Leo Bosch
    Intellectual 320 points

    I never said only 'main' should alter the power mode. Through this instruction "__biS_SR_register_on_exit(LPM2_bits );" I am changing the vlue of SR in stack. after executing ISR when t goes back it will load the altered value from the stack in the SR.
    Let the someone else advise. btw Thanks you tried to help me :)

  • 0 in reply to Luqman
    Guru 23000 points

    Luqman said:
    Through this instruction "__biS_SR_register_on_exit(LPM2_bits );" I am changing the vlue of SR in stack. after executing ISR when t goes back it will load the altered value from the stack in the SR.

    Wrong! You need to (re-)read the User’s Manual.

    Leo Bosch said:
    ‘on_exit’ means not now but when call is completely finished

    and Stack has been ‘popped’!

  • 0 in reply to Leo Bosch
    Intellectual 320 points

    yes you are right. When ISR will completely finish and stack will popup and it will go back to the position from where it was before interrupt generating It will start working again with changed Power mode.

    During ISR surely it will be in AM

  • 0 in reply to Luqman
    Guru 16361 points

    Luqman said:
    want when it goes back in main it goes in different mode. Specfiically in my code, It will come from LPM4 and it should go after completing call in LPM2. Am I right ?

    First of all there's a conflict between the two highlighted requirements. If the ISR ends and the stored SR register on the stack is set to LPM2, then execution will never get back to main - the CPU will be switched off. You can only resume execution of main by clearing the LPM bits to resume in active mode.

    The second problem with the latest code listing is that __bis_SR_register_on_exit(LPM2_bits); will do nothing if the MCU was in LPM4 before the ISR triggered. The set bits in LPM4_bits include all the set bits in LPM2_bits (plus some extra ones). If you want to exit the ISR in LPM2 then you'd need to do

    __bic_SR_register_on_exit(LPM4_bits); // Clear the LPM4 bits

    __bis_SR_register_on_exit(LPM2_bits); // Set the LPM2 bits

    or equivalently:

    __bic_SR_register_on_exit(LPM4_bits & ~LPM2_bits); // Clear the bits that are set in LPM4_bits but not set in LPM2_bits

    A common way to do this is to just clear the LPM4 bits in the ISR. Then the CPU will be active and execution continues in main, where the code can switch to LPM2 and set up any peripherals as required.

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