Atmel SAM4S-XPLD Atmel ATSAM4S-XPLD ATSAM4S-XPLD Hoja De Datos

 238

SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

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CPI (all instruction cycles except for the first cycle)

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Interrupt overhead

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 which can be
generated by three different sources with several priority levels:

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Software trace: Software can write directly to ITM stimulus registers. This can be done thanks to the “printf” 
function. For more information, refer to 

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Hardware trace: The ITM emits packets generated by the DWT.

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Time stamping: Timestamps are emitted relative to packets. The ITM contains a 21-bit counter to generate the 
timestamp.

The following example describes how to output trace data in asynchronous trace mode.

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Configure the TPIU for asynchronous trace mode (refer to 

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Enable the write accesses into the ITM registers by writing “0xC5ACCE55” into the Lock Access Register 
(Address: 0xE0000FB0)

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Write 0x00010015 into the Trace Control Register:

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Enable ITM

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Enable Synchronization packets

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Enable SWO behavior

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Fix the ATB ID to 1

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Write 0x1 into the Trace Enable Register:

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Enable the Stimulus port 0

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Write 0x1 into the Trace Privilege Register:

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Stimulus port 0 only accessed in privileged mode (Clearing a bit in this register will result in the 
corresponding stimulus port being accessible in user mode.)

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Write into the Stimulus port 0 register: TPIU (Trace Port Interface Unit)

The TPIU acts as a bridge between the on-chip trace data and the Instruction Trace Macrocell (ITM).

The TPIU formats and transmits trace data off-chip at frequencies asynchronous to the core.

The TPIU is configured in asynchronous mode, trace data are output using the single TRACESWO pin. The
TRACESWO signal is multiplexed with the TDO signal of the JTAG Debug Port. As a consequence, asynchronous trace
mode is only available when the Serial Wire Debug mode is selected since TDO signal is used in JTAG debug mode.

Two encoding formats are available for the single pin output:

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 Manchester encoded stream. This is the reset value.

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 NRZ_based UART byte structure

This example only concerns the asynchronous trace mode.

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Set the TRCENA bit to 1 into the Debug Exception and Monitor Register (0xE000EDFC) to enable the use of trace 
and debug blocks.

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Write 0x2 into the Selected Pin Protocol Register

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Select the Serial Wire Output – NRZ

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Write 0x100 into the Formatter and Flush Control Register