What problem arrise when we have union + volatile?

Hello all,

I have the following .c file:

typedef unsigned char U8;
typedef unsigned int U16;

union twoBytesUnion{
U16 a;
};

union twoBytesUnion var_AA;
volatile union twoBytesUnion var_BB;
volatile U16 var_CC;

U16 var_temp;

void main (void)
{
var_CC = 0;
var_temp = var_CC; // Green check - NIV

var_AA.a = 0;
var_temp = var_AA.a; // Green check - NIV

var_BB.a = 0;
var_temp = var_BB.a; // Orange check - NIV -> *Why? What problem arrise when we have union + volatile?*
}

Polyspace settings: "Ignore default initialization of global variables" - checked Char: 8bits Int: 16bits Alignment: 8bits.

The Polyspace says that the orange check "Variable var_BB that is declared volatile may lead to imprecise check". Why?

Answer 1

[Alexandre De Barros]

Hi Cristina,

It is indeed an imprecision when a volatile union is used. It has been reported and should be fixed in a future version.

So for the moment you can simply ignore it.

Best regards,

Alexandre