Keil IDE stopwatch not working in Debug mode

Question

I have been using ST F4-Discovery board for some time, as many of other friends. We all have the same problem. We are using Keil IDE (used different versions from 4.3 up to 4.7). Whenever we time anything using breakpoints and stopwatch, it works perfectly when in simulation mode. However, when we are debugging on-board and run the same code, the stopwatch never reports correct timing. It is actually random. Does anyone know what the problem is?

Thanks

Answer 1

I found the answer much later in time. It has to do with the internal debug circuitry. By default, the timer peripherals do not stop when we hit a breakpoint in debug mode but continue counting. This is why we keep getting random measurment intervals between timer interrupt instances using the stop watch. In order to get accurate timing, we need the debug circuity to force the timer peripheral to stop counting once we reach a breakpoint and resume later once we step over it. This can be done by writing this code:

SET_BIT(DBGMCU->APB1FZ, DBGMCU_APB1_FZ_DBG_TIM3_STOP);

Which instructs timer 3 on APB1 bus to stop counting at breakpoints.

Answer 2

Stopwatch is based on the internal register SEC. There seems to be a bug that if the register window is not showing then the stopwatch values are not updated. When debug is running select View|Register window and make sure you can see the SEC register value updating. The stopwatch in the status bar should now be updating too.

Answer 3

To solve the problem of the stopwatch, go to: Tarjet options - debug - setting - trace - core clock and adjust the frequency to 72MHz or core of your processor.