Cortex-A8 R2P2.pdf - ARM Information Center

Embedded Trace Macrocell14.1.2 The debug environmentMain FIFO The trace generated by ETM is in a highly compressed form. The mainFIFO enables bursts caused by the trace compression to be flattened out.When the FIFO becomes full, the FIFO signals an overflow. The tracegeneration logic does not generate any new trace until the FIFO hasemptied. This causes a gap in the trace when viewed in the debugger.You can also configure the ETM to suppress data address tracing whenthe FIFO is close to being full. This can prevent overflows fromoccurring.AMBA 3 ATB interfaceThe ETM outputs trace using the AMBA 3 Advanced Trace Bus (ATB)interface. See the CoreSight Architecture Specification for moreinformation on AMBA 3 ATB.You can output trace asynchronously to the core clock.AMBA 3 APB interfaceThe AMBA 3 Advanced Peripheral Bus (APB) interface enables accessto the ETM, CTI, and the debug registers. The APB interface iscompatible with the CoreSight architecture which is the ARMarchitecture for multi-processor trace and debug. See the CoreSightArchitecture Specification for more information.A software debugger provides the user interface to the ETM. The debugger enables allthe ETM facilities such as the trace port to be configured. The debugger also displaysthe trace information that has been captured.The ETM compresses the trace information and outputs it to the AMBA 3 ATBinterface. The ETM can then either:• Export the trace information through a narrow trace port. An external Trace PortAnalyzer (TPA) captures the trace information as Figure 14-1 on page 14-4shows.• Write the trace information directly to an on-chip Embedded Trace Buffer (ETB).The trace is read out at low speed using the JTAG or Serial Wire interface whenthe trace capture is complete as Figure 14-1 on page 14-4 shows.When the trace is captured, the debugger extracts the information from the TPA anddecompresses it to provide a full disassembly, with symbols, of the code that wasexecuted. The debugger can also link this back to the original high-level source code, toprovide you with a visualization of how the code was executed on the target system.ARM DDI 0344E Copyright © 2006-2008 ARM Limited. All rights reserved. 14-3