Problem with S12ZVC startup code

[amit_dhand]

Hello,

I have a created a short code to initialise MCU clock before going to _Startup code.

Here is the code.

#include <hidef.h> /* for EnableInterrupts macro */

#include "derivative.h" /* include peripheral declarations */

#include <starts12z.h>

void PLL_init();

void interrupt VectorNumber_Vreset Vreset_ISR();

void interrupt VectorNumber_Vreset Vreset_ISR()

{

    PLL_init();

}

void main(void)

{

  EnableInterrupts;

  /* include your code here */

  for(;;) {

    __RESET_WATCHDOG();    /* feeds the dog */

  } /* loop forever */

  /* please make sure that you never leave main */

}

void PLL_init()

{

    CPMUCLKS_PLLSEL = 1;                //FBUS = FPLL/2.   FBUS = 32MHz,

    CPMUREFDIV_REFFRQ = 1;                //Reference clock between 2MHZ and 6MHZ.   

    CPMUREFDIV_REFDIV = 0x1;            //FREF=8/(1+1) = 4MHZ       

    CPMUSYNR_VCOFRQ = 0x1;                 //FVCO is between 48MHZ and 80MHZ   

    CPMUSYNR_SYNDIV = 0x7;                //FVCO = 2xFREFx(SYNDIV+1)   =   FVCO = 2x4x(7+1) = 64MHZ

    CPMUPOSTDIV_POSTDIV = 0x0;            //FPLL = FVCO/(POSTDIV+1).  FPLL = 64MHZ/(0+1)    FPLL = 64MHz   

    CPMUOSC_OSCE = 1;                    //External oscillator enable. 8MHZ.        FREF=FOSC/(REFDIV+1)       

    while(!CPMUIFLG_LOCK){}                // Wait for LOCK.         

    CPMUIFLG = 0xFF;                    // clear CMPMU int flags - not needed but good practice

    __asm(jmp _Startup);                   /* Jump to C startup code */

}

I commented this part of code from LCF file

VECTOR 0 _Startup /* reset vector: this is the default entry point for a C/C++ application. */

But the issue is now every time I debug the code with the setting as program entry point, it always jump into the startup code. It never comes to this function PLL_init.

I would like to know how S12ZVC microcontroller is configured for the program startup.

Thank you,

Amit Dhand

[trytohelp]

Hi Amit,

I've created a short example based on S12ZVML128.

For the debug option I've selected Stop at entry function.

When I launch the debug session the application is loaded and point to void _Startup(void) function.

Now I added your code and commented the VECTOR 0 _Startup in prm file.

When I launch the Debugger, the application is loaded and point to the void _Startup(void) function too.

However if I click on reset, the application jump to the void interrupt VectorNumber_Vreset Vreset_ISR() function.

It should be the case on your side too.

Now the entry point is defined at _Startup function.

To change it you must define a new one and need to add in prm file (see add the end):

INIT Vreset_ISR

Now when I launch the debugger the application is loaded and point to:

     void interrupt VectorNumber_Vreset Vreset_ISR()

Have a great day,
Pascal
Freescale Technical Support
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[amit_dhand]

Hello Pascal,

Using keyword INIT in LCF file to start from the reset vector is fine. But I observed a weird thing that when the PLL_init function executes the first line of code it jumps to the undefined state.

Then to observe it more clearly I created a ProcessorExpert project for S12ZVC and generated the code.

I got the definition of ISR(Cpu_Interrupt) and I created a similar one for Vreset_ISR which called the _EntryPoint function

ISR(Cpu_Interrupt)

{

  /*lint -save -e950 Disable MISRA rule (1.1) checking. */

  asm(BGND);

  /*lint -restore Enable MISRA rule (1.1) checking. */

}

ISR(Vreset_Interrupt)

{

    _EntryPoint();

}

In LCF file

INIT Vreset_Interrupt

/* The entry point of the application. This function is generated into the CPU module. */

In vector.c vector table.

_VECTOR(Vreset_Interrupt)

/* 0x00FFFFFC  ivVreset

used by PE */

When I debug and execute first instruction of the _EntryPoint function, it jumps into this Cpu_Interrupt function and stays there.

Can you help me out on this situation.

Regards,

Amit Dhand

[trytohelp · Accepted solution]

Hi Amit,

It's true than the example code created it's not working.

I didn't checked it as it was not the problem.

And you're right with PEx code too.

The problem is the same in both cases.

The Stack pointer is not initialized and I don't know exactly how is it defined by default.

Have a look to the cpu.c file.

Extract of void _EntryPoint(void)

{

...

  /*lint -save  -e950 Disable MISRA rule (1.1) checking. */

  __asm(jmp _Startup);                /* Jump to C startup code */

  /*lint -restore Enable MISRA rule (1.1) checking. */

}

You can see the PEx code is not using c code to call the _Startup but the jmp assembly instruction.

The jmp is not saving the address function on stack.

It's important as the stack is not initialized in _EntryPoint but in _Startup only.

In the PEx example, if you change the code:

++++++++++++++

ISR(Vreset_Interrupt)

{

    _EntryPoint();

}

++++++++++++++

by:

++++++++++++++

ISR(Vreset_Interrupt)

{

    __asm(jmp _EntryPoint);                /* Jump to _EntryPoint code */

}

++++++++++++++

BACK to your Example code.

Just change the code:

void interrupt VectorNumber_Vreset Vreset_ISR();

void interrupt VectorNumber_Vreset Vreset_ISR()

{

    __asm(jmp PLL_init);

}

Now it's working.

Have a great day,
Pascal
Freescale Technical Support
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[amit_dhand]

Thank you Pascal, I also thought the stack initialisation could be an issue with you. But thanks for confirming it.

Regards,

Amit Dhand

[amit_dhand]

Thank you Pascal, This thing worked out.

Regards,

Amit Dhand