STM32F429I Discovery board - unable to do printf() redirection using SWV/ITM
Although Blargian already gave his answer as a comment, I thought I should formally answer in case anyone has the same problem.



I will refer to the document "STM32F429ZI Discovery Kit User Manual" (search for "en.DM00093903" or "UM1670") as "the user manual" in the below paragraphs.

In section 6.13 of the user manual, it indicates that solder bridge "SB9" controls the SWO (Serial Wire Out). By default, SWO is disconnected! This means you can't get any output back from the device for any of the SWV features.

To apply this fix, apply judicious solder to SB9, as indicated in Figure 4. of the user manual. It is located on the bottom side of the board (the side without the LCD), near the SWD connector.

If you apply this fix, note that PB3 will be connected to SWO, so you can't use PB3 anymore.



I think using an external ST-LINK/V2 debugger would also work (see section 6.3.5 of the user manual).

Also as Blargian mentioned, the clock speed must match the actual speed the microcontroller is running at.