Inav: LED_STRIP lock up on F4 compiled with GCC 7

[stronnag]

Continuation of #2372.

It has now been demonstrated that F4 hex for at least Matek F405OSD and Omnibus F4 Pro V3 that enabling LED_STRIP causes the board to lock up during initialisation (verified with gcc 7.2 and 7.3). Hex compiled with gcc 6.x are not affected.

[digitalentity]

This is a real pity. Any idea what might be causing this?

[digitalentity]

I'm going to have a crack at this bug. I have a gut feeling that it might be a buffer overflow issue yet again.

[digitalentity]

Nailed it. Hardfault was caused by division by zero in ledstrip code. For some reason the same code didn't yield a hardfault exception under GCC 6 and earlier.

Interestingly DIV_0_TRP exception is masked in both cases, so division by zero should yield zero result and not generate a fault. Maybe analyzing assembly listing may provide some insight but I'm too lazy to do it 😄

[stronnag]

good job. Always satisfying nailing this sort of problem.

[digitalentity]

And always amazingly hard to track.

[digitalentity]

Fix merged.