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Odd problem with SWO printf() output, STM32L152RET

Question asked by mcygnus on Jan 28, 2016
Latest reply on Feb 4, 2016 by mcygnus
I've turned up nothing relevant in forum and web searches, so I apologize in advance if it turns out I've overlooked something painfully obvious.

I'm experiencing an issue with (SWO) debug output via printf(). When I first start my app in my debugger, I see nothing. If I break and then continue execution, I see output. If I break, reset, and continue, I see nothing. I also see nothing using the ST-LINK Utility to monitor output. Now for details...

The target is an STM32L152RET. In order to speed initial development (I'm constrained by board production timelines), I bought an STM32L152C-Discovery board and replaced its xRCT µC with an xRET variant. I've updated the firmware in the board's ST-LINK to whatever's current.

My debugger is IAR's EWARM v. 7.50.2. My ST-LINK Utility is v. 3.8.0.

Previous early development code run on an unmodified Discovery board exhibited no issues. I've not changed any configurable parameters between that workspace and the new one I made today. I don't imagine it's a configuration issue anyway, considering that I do see my output after a break/resume in the debugger. The code appears to be running just fine otherwise, so I don't suspect a soldering issue.

Has anyone experienced this sort of behavior before?

Thank you very much in advance for any assistance!