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15.4
Trace output
ARM DDI 0337B
The ETM outputs data 8-bits at a time, at the core clock speed. It does not support
different trace port sizes and trace port modes. The TPIU is used to export trace output
off chip. This output is compatible with the ATB protocol.
Because AFVALID functionality is not supported, the trace port cannot flush data from
the ETM FIFO. However, with an 8-bit ATB port the FIFO always drains which makes
AFVALID unnecessary.
The Cortex-M3 system is equipped with an optimized TPIU that is designed for use
with the ETM and ITM. This TPIU does not support additional trace sources. However,
additional trace sources can be added if the TPIU has been replaced with a more
complex version, and more trace infrastructure.
Note
A trace ID register and output are provided for systems that use multiple trace sources.
The TPIU uses the 'formatted' trace output protocol. This means that there is no
requirement for an extra pin for TRACECTL signal.
Trace output from the ETM is synchronous to the core clock. There is an asynchronous
FIFO in the trace port interface. If you want to integrate the ETM into a multi-core
system, you might have to use an asynchronous ATB bridge.
Copyright © 2005, 2006 ARM Limited. All rights reserved.
Embedded Trace Macrocell
15-9
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