CCS/EK-TM4C1294XL: Not so optimized after all?

Ja Hv

Tool/software: Code Composer Studio

I just discovered, what I will call a compiler error. Or maybe an optimizer error?

I have this waiting loop:

us_delay=false;

while(!us_delay)
{
}

us_delay is set to true in a timer interrupt routine.

In assembly this code is converted to:

  movs r1,#0
  strb r1,[r4]
 
  ldrb r0, [r4]

$C$L1:
  cmp r0,#0
  beq $C$L1

In other words the reading of us_delay has been placed outside the loop! The loop continues forever!

R0 is actually set to 1 in the interrupt handler, but is somehow set back to 0 when leaving the handler. No apparent instruction does so, so it must be part of returning from a handler?

This is with optimization set to global. If I disable the optimization completely, it runs correctly.

I have not tried other optimization settings.

over 5 years ago

0 Bob Crosby over 5 years ago

TI__Guru 72500 points

Did you declare the variable us_delay as volatile? That keyword is necessary to tell the compiler/optimizer that the value can change outside the scope of the current thread.

0 Ja Hv over 5 years ago in reply to Bob Crosby

Intellectual 630 points

That was the little helper!

Thanks.

All that remains with this is, why the thread goes under Other Microcontrollers. I thought I placed it under CSS?

0 Bob Crosby over 5 years ago in reply to Ja Hv

TI__Guru 72500 points

Not sure why it showed up under "Other Microcontrollers". That is the proper group for EK-TM4C1294XL questions, but if you put it in the Code Composer Studio forum that is where it should be. I moved it to the CCS forum because it is more appropriate for this question.

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CCS/EK-TM4C1294XL: Not so optimized after all?