The ITM_SendChar() is therefore not implemented in the CMSIS file core_cm0plus.h which is why you will get a compiler/link error with the SWO lib. Note that Cortex M0 and Cortex M0+ devices (eg the STM32L053) dont have the ITM en SWO in its core (see datasheet).

DigitalIn in(PA_14) //SWCLK, breaks SWO viewer DigitalIn in(PA_13) //SWDIO, breaks SWO viewer DigitalIn in(PB_3) //SWO, breaks SWO viewer Note that the SWO, SWDIO and SWCLK pins may not be used for anything else or the SWO viewer wont work. Your code will still be able to use the Serial console as usual. Note that the nucleo firmware supports both the SWO and the regular Serial connection to the host PC simultaneously. The result in the SWV window of ST-LINK is shown below.

Make sure you select the correct systemclock in the Serial Wire Viewer window (84MHz for the F401, 180MHz for F446, 74MHz for F103).

Start the SWV when flashing has completed. Just compile as usual, save the file on your PC, import the file in ST-LINK and press 'target' and ''automatic mode''. The ST-Link Utility software may also be used to flash code produced by the online compiler. You need to download and install the ST-LINK Utility software found here. It is also possible to use a Segger J-Link SWO viewer when you have access to a Segger J-Link and the SWO port. The code was tested on an F401, F446 and F103 using the ST-LINK Utility software on the Host PC. Pc.printf('SWO failed to claim stdout ') Printf('Message on stdout redirected to SWO ') Swo.printf('CPU SystemCoreClock is %d Hz ', SystemCoreClock) Swo.printf(' Hello World from SWO ')

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