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Cortex-A8 Technical Reference Manual - ARM Information Center

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14.1 About the ETM<br />

14.1.1 ETM features<br />

Embedded Trace Macrocell<br />

The ETM is a CoreSight component designed for use with the CoreSight Design Kit. CoreSight<br />

is the <strong>ARM</strong> extensible, system-wide debug and trace architecture. The <strong>Cortex</strong>-<strong>A8</strong> processor<br />

implements the ETM architecture v3.3.<br />

For more information about CoreSight and ETM functionality, see the Embedded Trace<br />

Macrocell Architecture Specification and the CoreSight documentation listed in Additional<br />

reading on page xxiv.<br />

The ETM has the following main features:<br />

Core interface module<br />

The core interface module monitors the behavior of the processor.<br />

Trace generation<br />

The ETM generates a real-time trace that can be configured to include:<br />

• instruction tracing containing:<br />

— the addresses of executed instructions<br />

— passed or failed condition codes of the instructions<br />

— information about exceptions<br />

— context IDs.<br />

• data address tracing containing the addresses of data transfers as viewed by<br />

the <strong>ARM</strong> architecture.<br />

Note<br />

The <strong>Cortex</strong>-<strong>A8</strong> ETM does not support tracing of data values.<br />

Filtering and triggering resources<br />

You can filter the ETM trace such as configuring it to trace only instructions or<br />

data transfers in certain address ranges. You can also configure the ETM to filter<br />

based on the values of data transfers even though these cannot be traced. More<br />

complicated logic analyzer style filtering options are also available.<br />

The ETM can also generate a trigger that is a signal to the trace capture device to<br />

stop capturing trace.<br />

Main FIFO The trace generated by ETM is in a highly compressed form. The main FIFO<br />

enables bursts caused by the trace compression to be flattened out. When the<br />

FIFO becomes full, the FIFO signals an overflow. The trace generation logic does<br />

not generate any new trace until the FIFO has emptied. This causes a gap in the<br />

trace when viewed in the debugger.<br />

You can also configure the ETM to suppress data address tracing when the FIFO<br />

is close to being full. This can prevent overflows from occurring.<br />

AMBA 3 ATB interface<br />

The ETM outputs trace using the AMBA 3 Advanced Trace Bus (ATB) interface.<br />

See the CoreSight Architecture Specification for more information on AMBA 3<br />

ATB.<br />

You can output trace asynchronously to the core clock.<br />

<strong>ARM</strong> DDI 0344K Copyright © 2006-2010 <strong>ARM</strong> Limited. All rights reserved. 14-2<br />

ID060510 Non-Confidential

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