Debug in _WFI mode?

[himanshudoshi]

Hello to all,

I am trying to see, what's happening to the program inside the _WFI() mode, but when I try to do so in debug mode. It doesn't proceed further and forcefully we need to stop the debug operation. Does any body know how to deal with such a small issue??

Thanking you, 

-Regards,

Himanshu Doshi

[lpcxpresso_supp]

When the cpu encounters a WFI instruction, it basically goes into a simple low power mode, and will no longer execute any instructions until an interrupt is triggered, at which point it will wake up again and enter the appropriate interrupt handler. Thus whilst in WFI "mode", waiting for an interrupt to happen, your application has basically stopped executing.

From a debug point of view, depending on your debug tools, it is possible that your debugger might actually time out the debug connection whilst the cpu is in WFI "mode" if an interrupt is not triggered within a certain timeframe. But in most cases, your system will probably have at least one interrupt triggering on a regular enough basis (such as Systick, or another timer), for the WFI to effectively be "invisible" from the debug point of view.

Regards,

MCUXpresso IDE Support

[Carlos_Mendoza]

Hi Himanshu Doshi,

The execution of the WFI instruction will cause immediate entry to the sleep or deep sleep power modes, no more code is executed after this instruction. Sleep mode is exited automatically when an interrupt enabled by the NVIC arrives at the processor or a reset occurs. Please see the User Manual for details on which interrupt sources are connected to NVIC.

Hope it helps!

Best Regards,
Carlos Mendoza
Technical Support Engineer

[himanshudoshi]

Hello, Mr. Mendoza

Thank you very much for your reply. I am using SysTick_Handler to get the interrupt in WFI (sleep mode). And, there is a piece of code written in the SysTick_Handler. Can you suggest me how should I debug the code inside the SysTick???

The piece of code looks like this:

void SysTick_Handler(void)
{
asm(
"STR.W R3,[R7]\t\n"
"STR.W R4,[R3]\t\n"
"STR.W R5,[R4]\t\n"

);
}

Thanking you once again,

Regards,

Himanshu

[Carlos_Mendoza]

Hi Himanshu,

Are you able to set a breakpoint inside the systick handler? If the debug connection gets lost because of the low power mode being used you could try attaching to the system as explained to Simon.

Hope it helps!

Best Regards,
Carlos Mendoza
Technical Support Engineer

[himanshudoshi]

Hello Carlos Mendoza,

Thank you very much for your reply. As suggested by you, I have provided a toggle break point into the _WFI program, but while debugging, an error was flashing at the bottom of IDE: "Stalled on bus operation". I have restarted the IDE and try again but it's the same and also the same thing happened on the debugger configuration to make attach only option true. Can you comment on it??

How to debug a program in the _WFI mode??

Regards,

Himanshu 

[simonwyss]

According to the user manual UM10805 Page 80 it is NOT possible to debug the low-power modes. (http://www.nxp.com/docs/en/user-guide/UM10850.pdf )

But in the appnote AN11611 is written that the debugger can be reconnected. However, NXP doesn't write in the appnote, how the reconnection could be accomplished.

NXP, can you give use some advice? 

I also like to know, how I can restart the debugger if I had previous finished the debug session and the code has not changed until now (no recompilation and flashing required).

[Carlos_Mendoza]

Hi Simon,

You should use the "Attach Only" option in the debug configurations, this will allow you to debug a running system:

https://community.nxp.com/message/630604 

Hope it helps!

Best Regards,
Carlos Mendoza
Technical Support Engineer