1.1. About the System Trace Macrocell

The STM is a trace source that is integrated into a CoreSight system, designed primarily for high-bandwidth trace of instrumentation embedded into software. This instrumentation is made up of memory-mapped writes to the STM Advanced eXtensible Interface (AXI) slave, which carry information about the behavior of the software.

The STM is a natural successor to the CoreSight Instrumentation Trace Macrocell (ITM) in mid- to high-performance applications. The STM provides the following advantages over the ITM for software instrumentation:

In addition to the AXI slave, the STM provides a hardware event interface. The STM traces when rising edges occur on signals connected to this interface. Alternatively, advanced custom system tracing features can be implemented by generating AXI write accesses directly to the AXI slave.

Figure 1.1 shows the STM integrated into a typical system.

Figure 1.1. STM system integration

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The STM AXI slave is connected to a system interconnect which enables all system masters, such as processors and DMA controllers, to generate trace by writing to the STM stimulus ports. For interaction with DMA controllers, the STM provides a DMA request interface compatible with the AMBA DMA Controller DMA-330.For configuration purposes, the STM is connected to Debug APB so that it can be accessed by off-chip and on-chip debug agents.CoreSight authentication signals are used to control debug permissions.The STM trace stream is output through the ATB interface and integrated with the rest of the CoreSight trace infrastructure.

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