Sometimes it is very useful to attach a debugger to an already running target. With the STM32CubeIDE, the ability exists but is a bit convoluted to activate. This turns out to work:
- start with your existing debug configuration, under Run|Debug Configurations…
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Duplicate it and rename it to “Attach”
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In Main, disable auto build
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In Debugger, uncheck “Verify flash download”, and set the reset behavior to “None”.
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In Startup, edit all the load images to no longer download
The option Debugger|Reset behaviour tells GDB what to do after it attaches:
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Connect Under Reset will put the device in reset, then connect
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Software System Reset will connect, then trigger a software reset
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None will keep the device running