Function call in isr

Hallo

I do have some generel question when calling a function from a isr.

I do see some strange behavior when doing it, depending on compiler optimization level and code.

When calling a function from the isr, that do some float operation on some data, I get a data abort exception or a program abort exception. When running the same code with compiler optimization level 1, I get an spourios interrupt instead.?

But if I remove the floating point calculation in the function, I dont have any problems. (No exception or spurios interrupt)

I know its generally not a good idea to call function from ISR. I dont intend to do that.
It just caught my attention why I get this strange behaviour?
Has it something todo with calling non static function?
I just would like to understand the reason...

See code sample below..

I dont use any Rtos. Im running on a LPC2103 and uVision 3.40

// ISR from the SPI..
void SPI_Isr(void) __irq
{
  // Read the SPI status register
  if ((S0SPSR & 0xF8) == 0x80)
  {
    // Switch on state
    switch(bySPIState)
    {
       ... do stuff....
       case 2:
       {
         .. reading SPI register ...
        // Store sample                         lConversionData[bChanl] =  lTempConversion;

         // After a short time the exception occure
         // in the Update
         Update();
         state = SPI_OK; // transfer completed
       }
       break;
     }
   }
   else // SPI error
   {
      .. error handling here
      state = SPI_ERROR;
   }
   // Reset  SPI interrupt flag
   S0SPINT = 0x01;
   // ACK the interrupt
   VICVectAddr = 0;
}

void Update(void)
{
         fTemp = (lConversionData[bChanl]&0xFFFFF)
                   *0.001497268677; // mV
        fTemp = fTemp/150;

        // Is the sign bit set?
        if((lConversionData[bChanl]&0x200000) ==
             0x200000                     ) // Signed?
        {
                fTemp *= -1;
        }
        protocol_UpdateData(WEIGHTCELL_MODULE,
                       m_byCurrentChannel, fTemp, 0);
}

So, if I move the code inside the Update() to the SPI isr, no problems!!

Calling the Update() i get the explained behaviour?

But I i just remove the "0.001497268677" value from the equation, no problemas?

If I remove the lConversionData[bChanl] no problems?

Why?

/Thomas