doc: services: debugging: Add Coresight Trace Deformatter documentation

Add documenation for Coresight Trace Deformatter.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>

doc/services/debugging/cs_trace_defmt.rst

@@ -0,0 +1,23 @@
+.. _cs_trace_defmt:
+
+ARM Coresight Trace Deformatter
+###############################
+
+Formatter is a method of wrapping multiple trace streams (specified by 7 bit ID) into a
+single output stream. Formatter is using 16 byte frames which wraps up to 15 bytes of
+data. It is used, for example, by ETR (Embedded Trace Router) which is a circular RAM
+buffer where data from various trace streams can be saved. Typically tracing data is
+decoded offline by the host but deformatter can be used on-chip to decode the data during
+application runtime.
+
+Usage
+#####
+
+Deformatter is initialized with a user callback. Data is decoded using
+:c:func:`cs_trace_defmt_process` in 16 bytes chunks. Callback is called whenever stream changes or
+end of chunk is reached. Callback contains stream ID and the data.
+
+API documentation
+*****************
+
+.. doxygengroup:: cs_trace_defmt

doc/services/debugging/index.rst

@@ -12,3 +12,4 @@ Debugging
    debugmon.rst
    mipi_stp_decoder.rst
    symtab.rst
+   cs_trace_defmt.rst