The Cortex-M3 is configured by default in JTAG mode. But the SAM3U also supports the Serial Wire Debug (SWD) mode which reduces the number of pins dedicated for debug. Only two are necessary: SWCLK and SWDIO. An extra one called TRACESWO is dedicated to the Asynchronous Trace (ITM) feature that is also supported. Serial Wire Debug mode as well as Asynchronous Trace (ITM) are both supported by the JTAG SAM-ICE. The table on this slide shows the different pins which are used in JTAG and in Serial Wire and Asynchronous Trace.