MCU Performance: running with emulator vs running without emulator

Question

If I connect to my MCU with its SWD emulator/debugger, is there ANY difference in performance/behavior as compared to when I run the MCU without the emulator?

EDIT: I am using a freescale KL25z Cortex M0+ with Arm GCC compiler on Eclipse. I am running at full speed.

• KyranF: That's very vague, you did not tell us which MCU, which debugger you were using, what IDE you were using, what settings you have (maybe there is full speed, or slow-mode for debugging in real time easier). I would say yes, there is a difference both in behaviour and performance - slower speed because of clock cycles used to communicate and share the core/register data contents, and different behaviour as interrupts may not work as intended and there are more pins in use than normally withour the SWD connected.
• hassan789: I see...also, I have added the information you requested
• KyranF: cool! Well I have not used SWD before, only JTAG for the processor used on the Beaglebone (the huge-ass AM3358) so I will not provide a full answer. wait until somebody with more direct experience on this matter answers :)

Answer 1

In a word, yes.

As a rule of thumb, a debugger will slow down the target chip. The more expensive real time debugger/ICE tools reduce this but you will still get a measurable slow down.

The slow down is typically because the debugger sticks extra code into your program for breakpoints, RAM monitoring etc.

How much slow down is rather a "how long is a piece of string" question. Your best bet is to measure it.

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Word to the wise

Always test your code comprehensively without a debugger. It is entirely possible to write embedded code that only works when the debugger is plugged in (the debugger slow down fixes timing issues inadvertently).