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FPU issue in function call (STM32F407 and STM32F429)

Posted by ezinger on 2016-05-10 09:37

Hello,

i recognized a strange behavior between STM32F407 and STM32F429 librarys. I tried to convert a double to string with a simple function i wrote by myself.

void double2str( double value, char *str, uint8_t precision );


If i use a simple code just convert a single double and transmit this with USART the STM32F407 get stuck (Hardware fault). If i use the identical code at STM32F429 everything is fine.
I tried to use a pointer for the double value and it works at the STM32F407:

void double2str( double *value, char *str, uint8_t precision )
(
double val2 = *value;
...


So something ist worng with the function call and the double value.
Is there a way to fix this?

I can not change hard ABI to soft, or softfp. This causes many errors in the StandardPeripheralLibraries while building the project.

Thanks, Erik

Reads: 6017
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Posted by MattReed59 on 2016-05-10 15:14

Erik, We need more info to go on. If you could post the entire double2str routine.
And, what kind of hard-fault? Usually a hard-fault means something wrong with the stack, if there were an FP error you would just get the wrong number.
Have you tried stepping through the routine in the debugger?

-Matt

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Posted by ezinger on 2016-05-12 06:43

Hello,

the function “double2layer” has no important content. It is just the double value given to the function which causes the error. (i earased the whole content - the fault still happens)

void double2str( double value, char *str, uint8_t precision )
{
if( value >= 0 )
*(str++) = ‘+’;
else{
*(str++) = ‘-‘;
value = -value;
}
}

If i copy this function into the calling routine everything works fine.
Or this way works too:

void double2str( double *val, char *str, uint8_t precision )
{
double value = *val;

if( value >= 0 )
*(str++) = ‘+’;
else{
*(str++) = ‘-‘;
value = -value;
}
}


When i try to debug i get into this at the function call:

/**
* @brief This is the code that gets called when the processor receives an
* unexpected interrupt. This simply enters an infinite loop, preserving
* the system state for examination by a debugger.
* @param None
* @retval None

  • /

.section .text.Default_Handler,”ax”,%progbits
Default_Handler:
Infinite_Loop:
b Infinite_Loop
.size Default_Handler, .-Default_Handler

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