Sometime Cant connect to device using St utility on STM32F767

[HIzzu]

I've developed a device with an STM32F767ZIT6 on it. A custom board.

It was always can connect with ST-Link Utils in the beginning but overtime it is very difficult to connect (Cant connect to device) but sometimes it can.

I cant find where the problem comes from, is it power rail problem or what?

Schematics & layout below

[Uwe Bonnes]

This may depend on what is running on the target. E.g. you can't attach to a programm in deep sleep without some mean to wake up the CPU ( Reset, or wait for wakeup.) Tight loops "while (1);" are also hard to attach too.

[HIzzu]

The target is empty, no program in it.

but after we erased the flash, it is very difficult to connet.