10.4.1. Modes of operation

The formatter supports the following distinct modes of operation as specified by bits[1:0] in the FFCR, described in ETB Formatter and Flush Control Register:

Bypass

In this mode, no formatting information is inserted into the trace stream and a raw reproduction of the incoming trace stream is stored.

When trace is stopped, an additional byte of value 0x01 is written, followed by bytes of 0x00 to align the trace to a 32-bit boundary. This can be used by a trace decompressor to find the last byte of trace.

Note

  • This mode assumes that the source ID does not change.

  • To select this mode, set FFCR.EnFTC to 0 and FFCR.EnFCont to 0.

Normal

Formatting information is added to indicate the change of source ID together with the associated wrapping additions, as described in ARM® CoreSight™ Architecture Specification. When tracing is stopped, the formatter frame is filled with bytes of trace with ID 0x00 if necessary to complete the frame.

To select this mode, set FFCR.EnFTC to 1 and FFCR.EnFCont to 0.

Continuous

Continuous mode in the ETB corresponds to normal mode with the embedding of triggers. Most usage models use this mode, and modern debug tools do not normally require the other modes. Unlike continuous mode in the TPIU, no formatter synchronization packets are added because the formatted trace frames are always aligned to the RAM address.

To select this mode, set FFCR.EnFTC to 1 and FFCR.EnFCont to 1.

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