Today I have started to encounter strange problems with SWD debugging.

The debug only works if I keep my finger on the SWD pins. To be more interesting I have the same problem with the boards I was working in the past without any problems. All Vdd and Vss are connected correctly - checked many times.

I am trying to sort this problem for two days and have run out of the fresh ideas what actually can cause this problem.

Any help appreciated.

  • 2
    \$\begingroup\$ puuuuuh. Hmmmm. First of all: mechanical problems. are your solder joints and connectors intact? then: What's the ground used by your SWD programmer? Is it definitely the same as the the one of your STM32? Then: EMI – maybe your finger is absorbing RF noise, but that would be a peculiar kind of luck. Is there something switching very high currents or very fast on your board/in your vicinity? Got an oscilloscope to probe the SWD lines during (non-)operation? \$\endgroup\$ – Marcus Müller Mar 3 '19 at 13:27
  • \$\begingroup\$ @MarcusMüller Nothing. As I wrote I try to sort out this problem for two days. Strange that my other boards behave the same now as well. (two different debug probe tested). I have tired literally everything. \$\endgroup\$ – P__J__ Mar 3 '19 at 13:41
  • \$\begingroup\$ That makes the EMI problems more likely. What about that oscilloscope? Do you have one, how much bandwidth does it muster? \$\endgroup\$ – Marcus Müller Mar 3 '19 at 13:44
  • \$\begingroup\$ To be more interesting the problem is only with the stm32F3 boards. All other work OK \$\endgroup\$ – P__J__ Mar 3 '19 at 13:46
  • \$\begingroup\$ Lines are clear. No noise \$\endgroup\$ – P__J__ Mar 3 '19 at 13:46

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