Access ETM only with code without the use of debug kits

[lorenrus]

My board is Nucleo F401RE.

 My board is Nucleo F 401 RE

This is the first time I've ever been doing this.

I am using a pointer to the main registry of ETM, its address I read it on the datasheet.

I would like to change the bits of this log but I do not change it the correct way.

 my code:

#define ETM_CR 0xE0042000 //Address

unsigned int *pointer = (unsigned int *) ETM_CR;

unsigned int var = 0;

var = *pointer

printf("Value of var: %d\n, var)

now i want to modify *pointer, for example:

*pointer = 0x1;

Now i expected to have in *pointer 0x1 but there insn't 0x1, there ins't the last value but there is another value.

Thank you

[lorenrus]

Someone can help me ?

Thanks

[devan]

Unfortunately, it's not always possible to write to debug registers like the ITM/ETM unless an external debugger has already connected to the core and enabled debugging.

See one of the following links for more discussion on this:
https://community.arm.com/tools/f/discussions/796/output-data-via-swo-without-debugger
http://essentialscrap.com/tips/arm_trace/theory.html

This is kind of disappointing, since there are cases where it would be convenient to collect trace data with a logic analyzer without also having to connect a debugger.

[andersm]

The address of the ETMCR register is 0xE0041000. To write to the ETM registers, you first need to unlock the ETMLAR register. Useful documents:

• CoreSight ETM‑M4 Technical Reference Manual
• Embedded Trace Macrocell v3 Architecture Specification
• Cortex‑M4 Processor Technical Reference Manual
• STM32F401 Reference Manual

[lorenrus]

Hi and thanks for the reply.

To unlock ETM_LAR I have to write to his memory cell the value 0xC5ACCE55.
To do this assignment I thought I'd do it with pointers this way

#define ETM_LAR 0xE0041FB0 // Address of  ETM_LAR

#define UNLOCK 0xC5ACCE55 // Value to unlock the ETM

int main (void)

{

unsigned int *pointer_1 = (unsigned int *) ETM_LAR;  //  The pointer_1 will point to the address contained in the variable ETM_LAR
                                                                                     
*pointer_1 = UNLOCK;  // Cheque UNLOCK to the contents of the memory address ETM_LAR

}

is correct ?

Thank you

[lorenrus]

Hi and thanks for the reply.

To unlock ETM_LAR I have to write to his memory cell the value 0xC5ACCE55.
To do this assignment I thought I'd do it with pointers this way

#define ETM_LAR 0xE0041FB0 // Address of  ETM_LAR

#define UNLOCK 0xC5ACCE55 // Value to unlock the ETM

int main (void)

{

unsigned int *pointer_1 = (unsigned int *) ETM_LAR;  //  The pointer_1 will point to the address contained in the variable ETM_LAR
                                                                                     
*pointer_1 = UNLOCK;  // Cheque UNLOCK to the contents of the memory address ETM_LAR

}

is correct ?

Thank you

[ajb]

That should work, but you can include the dereference and pointer typecast in the define make it much more concise:

Code: [Select]

#define ETM_LAR *((unsigned int *)0xE0041FB0) // Address of  ETM_LAR

#define UNLOCK 0xC5ACCE55 // Value to unlock the ETM

int main (void)

{

    ETM_LAR = UNLOCK;  // Cheque UNLOCK to the contents of the memory address ETM_LAR

}


[lorenrus]

That should work, but you can include the dereference and pointer typecast in the define make it much more concise:

Code: [Select]

#define ETM_LAR *((unsigned int *)0xE0041FB0) // Address of  ETM_LAR

#define UNLOCK 0xC5ACCE55 // Value to unlock the ETM

int main (void)

{

    ETM_LAR = UNLOCK;  // Cheque UNLOCK to the contents of the memory address ETM_LAR

}


Hi and thanks for reply

Yes , also I did the same thing but the problem is that I think I do not change physically, but I change only the value of the variable.

Thanks