Stack Pointer / Program counter

[CCandido]

Hi,

how to control the PC, to return to a function address ?.

funtion ( my_task, absolute addres )

set Stack Pointer initial value

set program  counter

goal is when there is an error in the program.

the ISR_timer  resets and returns the program,  to the beginning.

hope you understand, thank you.

[yasuhikokoumoto]

Hello carlos candido,

although I cannot catch your intention, do you wat to change the return addresses of the __ISR_times_1oous()?

The __ISR_times_1oous should be invoked by the intermediate function as the following.

void __attribute__ (( naked )) __ISR_times_1oous(void) /* for normal gcc */
{
asm volatile(
"movs r0, #4¥t¥n"
"mov r1, lr¥t¥n"
"tst r0, r1¥t¥n" /* Check EXC_RETURN[2] */
"beq 1f¥t¥n"
"mrs r0, psp¥t¥n"
"ldr r1,=__ISR_times_1oous_main¥t¥n"
"bx r1¥t¥n"
"1:mrs r0,msp¥t¥n"
"ldr r1,=__ISR_times_1oous_main¥t¥n"
: /* no output */
: /* no input */
: "r0" /* clobber *
);

or

void __stackless __ISR_times_1oous(void) /* for IAR gcc */
{
asm volatile(
"movs r0, #4¥t¥n"
"mov r1, lr¥t¥n"
"tst r0, r1¥t¥n" /* Check EXC_RETURN[2] */
"beq 1f¥t¥n"
"mrs r0, psp¥t¥n"
"ldr r1,=__ISR_times_1oous_main¥t¥n"
"bx r1¥t¥n"
"1:mrs r0,msp¥t¥n"
"ldr r1,=__ISR_times_1oous_main¥t¥n"
: /* no output */
: /* no input */
: "r0" /* clobber *
);

and, in both cases,

void __ISR_times_1oous_main(unsigned int *intr_args)
{
     intr_args[6]="return address"
}

I hope these will help you.

Best regards,

Yasuhiko Koumoto.

[CCandido]

Hi  Yasuhiko Koumoto,

I used your code, PEX projets.

void __ISR_times_1oous_main(unsigned int *intr_args) 

{ 

      uint32_t a=0,b=0;

                           TI1_Enable( ); // timer off

                LED1_On();

                     //return from ram....

                    // how to , clear all register to re-start ?

  for(;;) {

                            // load_my_code()];

                       // call_execute_code_in_ram ();

                   a++;

                   b++;

   }

}

//---------------------------------

void TI1_OnInterrupt(void)             timer 1 ms PE project

{

    asm volatile(

     "MOVS r0, #4\t\n"

          "MOV  r1, LR\t\n" 

          "TST  r0, r1\t\n"  /// Check EXC_RETURN[2] 

          "BEQ  1f\t\n"

          "MRS  r0, PSP\t\n"

           "LDR  r1,=__ISR_times_1oous_main\t\n"

          "BX   r1\t\n"

          "1:   MRS  r0, MSP\t\n" 

          "LDR  r1,=__ISR_times_1oous_main\t\n"

  );

}

//--------------------------------------------------

lack only reset the variables and registers, to launch the application again.

I have to turn off the timer in return because it causes error.

tks,

Carlos.

[yasuhikokoumoto]

Hello,

you should not describe asm statement in a normal function.

The function will use the stack and then the asm statement will be useless.

Untill reach the __ISR_times_1oous_main, the stack pointer must not change.

So I added '__stackless__' attribute to the function.

The attribute will be valid for IAR's EWARM,

If you use GCC, the attribute would be '_attribute__((naked))'.

Best regards,

Yasuhiko Koumoto.

[Hui_Ma]

Hi Carlos,

Please let us know if your issue be resolved?

Thank you for the attention.

Have a great day,
Ma Hui

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[CCandido]

Hi Ma,

I tested your code, step 1 = ok.

lack only reset the variables and registers, to launch the application again.

I have to turn off the timer in return because it causes error.

if you can do the reset ALL, thank you.

see code( simulator ).

tks.

Carlos.

[Hui_Ma]

Hi Carlos,

Please check below code about how to jumper to application code:

//-----------------------------------------------------------------------------

// FUNCTION:    JumpToUserApplication

// SCOPE:       Bootloader application system function

// DESCRIPTION: The function startup user application

//             

// PARAMETERS:  pointer on user vector table

//             

// RETURNS:     function never go back

//----------------------------------------------------------------------------- 

void JumpToUserApplication(LWord userSP, LWord userStartup)

{

    // set up stack pointer

  __asm("msr msp, r0");

  __asm("msr psp, r0");

  // Jump to PC (r1)

  __asm("mov pc, r1");

}

The Kinetis Initial PC located at address 0x0000_0004;

the initial Stack Pointer at address 0x0000_0000;

Wish it helps.

Have a great day,
Ma Hui

-----------------------------------------------------------------------------------------------------------------------
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[CCandido]

Hi Ma,

my problems it Returned from ( execute code ram ) case have error.

ISR time periodic in Flash, case error ( exit to ) flash programa monitor.

//---------------------------------------------------------

void TI1_isr (void){  my timer in flash = 100uS.

-----

-----

return      _Nomals

or

return             _exit_to_flash_address

}

//---------------------------------------------------------------------

            void TI1_isr (void){            <-----Disassembly ( cw10.5 )

           push {r7}             <----- r7 = PC program counter ?  saved

          add r7, sp, #0

             }

     mov sp, r7

      pop {r7}

      bx lr

      nop

whats register load PC ( address pointer my code flash to return )?

tks,

Carlos.

[Hui_Ma]

Hi Carlos,

From <<Cortex™-M4 Devices Generic User Guide>> page16, there provides the processor core registers info below:

The PC at R15:

Have a great day,
Ma Hui

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[CCandido]

Hi Ma,

I need an equivalent way to use the HC08, but with Kinetis.

you can make the output of Ram program, within a timer ISR.

the variables does not matter anymore, go back to the task and restart it.

See example exit:

__interrup_timer_100us_isr()

....  if(  exit  ) {

   __asm ldhx  , #_my_address_task_in_flash             // load Stack

   __asm txs;                 // store H:X into the SP

    __asm rti;                 // return from interrupt

           }

}

tks,

Carlos.

[Hui_Ma]

Hi Carlos,

Please also consider the ARM Thumb bit: function pointers (and vectors pointers) have the Thumb bit set in the address, to mark that they are thumb functions.

So when using the ARM Thumb instruction, the really PC address should plus 0x1.

Wish it helps.

Have a great day,
Ma Hui

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