Trace is initialized in the user application, but the trace output does not appear on the SWO pin when the target is used in standalone mode (i.e. not connected to a BlueBox debugger).
On Arm Cortex devices the SWO trace pin can only be used in combination with
SWD (Serial Wire Debug), because the same pin is also used for the TDO signal
used by the JTAG interface. On S32K1xx controllers the debug port always comes
out of reset in JTAG mode and can only be switched to SWD mode by a specific
sequence which is sent by an external device. For this reason, when the
S32K1xx controller is reset in standalone operation the SWO pin is initialized
to be used as JTAG TDO signal, hence the expected trace output does not appear
on this pin.
Always use a BlueBox when observing the SWO trace signal by an oscilloscope. The BlueBox will automatically send the JTAG to the SWD switch sequence when winIDEA attaches to the S32K1xx controller. After the switch to SWD has occurred, the trace messages will appear on the SWO pin and can be observed by an oscilloscope.
The complete set-up required to observe the SWO trace signal:
More detailed information about this topic can be found in the S32K1xx Reference manual (section 58.3) and the Arm Cortex documentation.
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