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2.2.3. Formatter and stop sequence

When EnFt in the FFCR is set, formatting is enabled. For more information about the formatting protocol, see the CoreSight Architecture Specification.

Depending on the configuration of the TMC, trace might be written up to 256 bits at a time. Additionally, when the formatter is enabled by setting the EnFt bit in the FFCR, a whole number of frames must be written. When stopping trace capture, the TMC pads the end of the trace so that every byte of trace that has been accepted by the TMC is written.

Formatter enabled

If the formatter is enabled when trace capture is stopped, then the traces are padded in the formatted frames with additional bytes of data with a value of 0x00 and an ID of 0x00, until the following conditions are met:

  • A whole number of frames have been generated.

  • The trace is aligned to the memory width. This means that if the ATB interface is configured to 128 bits, then a multiple of two frames has been generated to meet the 256-bit memory width.

In Hardware FIFO mode, the ATB master interface does not generate any additional traces at the end of trace. However, all trace stored internally is flushed out of the TMC when trace capture is stopped.

Formatter disabled

Disabling the formatter is deprecated, and is supported in Circular Buffer mode only. If the formatter is disabled when trace capture is stopped, then the trace is padded with additional bytes so that the precise end of the trace can be determined, as follows:

  • a single byte of value 0x01, to indicate the position of the last byte before the stop sequence

  • zero of more bytes of 0x00, to align to the memory width.

Flexibility in the length of the stop sequence

The stop sequence might be longer than required to meet the above rules, to simplify the implementation.

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