When your application runs in C-SPY, printf style output is sent to Terminal I/O. To instead send text strings character by character to the trace output stream via the ITC register, available for SiFive devices with an Instrumentation Trace Component (ITC), specify this option on the ILINK command line:

‑‑redirect __dwrite=__dwrite_itc

This replaces the standard C-SPY debug write string support routine __dwrite with the ITC debug write string support routine.