Information

9.8 ITM
The ITM is an application-driven trace source that supports printf style debugging to
trace Operating System (OS) and application events, and emits diagnostic system
information. The ITM emits trace information as packets. There are four sources that can
generate packets. If multiple sources generate packets at the same time, the ITM
arbitrates the order in which packets are output. The four sources in decreasing order of
priority are:
1. Software trace -- Software can write directly to ITM stimulus registers. This emits
packets.
2. Hardware trace -- The DWT generates these packets, and the ITM emits them.
3. Time stamping -- Timestamps are emitted relative to packets. The ITM contains a
21-bit counter to generate the timestamp. The Cortex-M4 clock or the bitclock rate of
the Serial Wire Viewer (SWV) output clocks the counter.
4. Global system timestamping. Timestamps can optionally be generated using a
system-wide 48-bit count value. The same count value can be used to insert
timestamps in the ETM trace stream, allowing coarse-grain correlation.
9.9 Core Trace Connectivity
The ITM can route its data to the TPIU. (See the MCM (Miscellaneous Control Module)
for controlling the routing to the TPIU.) This configuration enables the use of trace with
low cost tools while maintaining the compatibility with trace probes.
9.10 TPIU
The TPIU acts as a bridge between the on-chip trace data from the Embedded Trace
Macrocell (ETM) and the Instrumentation Trace Macrocell (ITM), with separate IDs, to a
data stream, encapsulating IDs where required, that is then captured by a Trace Port
Analyzer (TPA). The TPIU is specially designed for low-cost debug.
9.11 DWT
The DWT is a unit that performs the following debug functionality:
ITM
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
188 Freescale Semiconductor, Inc.