Embedded Trace Macrocell
ARM DDI 0500D Copyright © 2013-2014 ARM. All rights reserved. 13-5
ID021414 Non-Confidential
13.3 ETM trace unit functional description
This section describes the ETM trace unit. It contains the following sections:
• Processor interface.
• Trace generation.
• Filtering and triggering resources.
• FIFO.
• Trace out on page 13-6.
• Syncbridge on page 13-6.
Figure 13-1 shows the main functional blocks of the ETM trace unit.
Figure 13-1 ETM functional blocks
13.3.1 Processor interface
This block monitors the behavior of the processor and generates P0 elements that are essentially
executed instructions and exceptions traced in program order.
13.3.2 Trace generation
The trace generation block generates various trace packets based on P0 elements.
13.3.3 Filtering and triggering resources
You can limit the amount of trace data generated by the ETM, through the process of filtering.
For example, generating trace only in a certain address range. More complicated logic analyzer
style filtering options are also available.
The ETM trace unit can also generate a trigger that is a signal to the trace capture device to stop
capturing trace.
13.3.4 FIFO
The trace generated by the ETM trace unit is in a highly-compressed form. The FIFO enables
trace bursts to be flattened out. When the FIFO becomes full, the FIFO signals an overflow. The
trace generation logic does not generate any new trace until the FIFO is emptied. This causes a
gap in the trace when viewed in the debugger.
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