Datasheet

205
11011B–ATARM–21-Feb-12
SAM3N
When the Serial Wire Debug Port is active, TDO/TRACESWO can be used for trace. The asyn-
chronous TRACE output (TRACESWO) is multiplexed with TDO. So the asynchronous trace
can only be used with SW-DP, not JTAG-DP.
SW-DP or JTAG-DP mode is selected when JTAGSEL is low. It is not possible to switch directly
between SWJ-DP and JTAG boundary scan operations. A chip reset must be performed after
JTAGSEL is changed.
11.5.3.1 SW-DP and JTAG-DP Selection Mechanism
Debug port selection mechanism is done by sending specific SWDIOTMS sequence. The JTAG-
DP is selected by default after reset.
• Switch from JTAG-DP to SW-DP. The sequence is:
– Send more than 50 SWCLKTCK cycles with SWDIOTMS = 1
– Send the 16-bit sequence on SWDIOTMS = 0111100111100111 (0x79E7 MSB first)
– Send more than 50 SWCLKTCK cycles with SWDIOTMS = 1
• Switch from SWD to JTAG. The sequence is:
– Send more than 50 SWCLKTCK cycles with SWDIOTMS = 1
– Send the 16-bit sequence on SWDIOTMS = 0011110011100111 (0x3CE7 MSB first)
– Send more than 50 SWCLKTCK cycles with SWDIOTMS = 1
11.5.4 FPB (Flash Patch Breakpoint)
The FPB:
• Implements hardware breakpoints
• Patches code and data from code space to system space.
The FPB unit contains:
• Two literal comparators for matching against literal loads from Code space, and remapping to
a corresponding area in System space.
• Six instruction comparators for matching against instruction fetches from Code space and
remapping to a corresponding area in System space.
• Alternatively, comparators can also be configured to generate a Breakpoint instruction to the
processor core on a match.
11.5.5 DWT (Data Watchpoint and Trace)
The DWT contains four comparators which can be configured to generate the following:
• PC sampling packets at set intervals
• PC or Data watchpoint packets
Table 11-2. SWJ-DP Pin List
Pin Name JTAG Port Serial Wire Debug Port
TMS/SWDIO TMS SWDIO
TCK/SWCLK TCK SWCLK
TDI TDI -
TDO/TRACESWO TDO TRACESWO (optional: trace)