TM172PDG18R - watchdog violations from unused local variable in Timed task

[obscuresc]

Hi,

I am able to reliably cause a watchdog violation in Timed task due to having a large unused local variable in a function. See function below.

Spoiler

FUNCTION stack_overflow: BOOL

VAR
test_string : STRING[ 3200 ];
END_VAR

stack_overflow := TRUE;
RETURN;

and the Timed program

Spoiler

IF test THEN;
test := FALSE;
ret := stack_overflow();
END_IF;

I set 'test' true via Debugging. A string of 3200 characters is pretty big but in my project that I first noticed this, I had a couple of strings ~64 characters long, but still not used in code.

Should the compiler determine that this variable is not used, and not compile it in to code?'

This is with EcoStruxure v1.10.0 for BIOS 668.17.

Thanks!

[FedericoM · Accepted solution]

Hello,

variable allocation is optimized for POU, Function Block and global variables.

I confirm that in case of functions all declared variables are allocated regardless of their usage.

At the moment, it is not in the roadmap an optimization of the compiler for this topic, it might be planned a stack control in the future bios version (not defined yet in which bios version).