4.11.1. Periodic synchronization

When the PTM receives a periodic synchronization request it generates all three synchronization packets. A periodic synchronization request is generated when any of the following occurs:

When the PTM receives a periodic synchronization request it generates the synchronization packets in the following order:

  1. A-sync.

  2. I-sync.

  3. T-sync.

When the Programming bit is cleared or the OS Lock is cleared, the PTM must generate the A-sync and I-sync packets before generating any other trace:

  1. The A-sync packet must be generated as the first packet.

  2. This is followed by a nonperiodic I-sync packet. This is generated when trace is turned on, unless a trigger occurs before trace is turned on.

  3. The PTM must generate a T-sync packet, but this might not be output immediately after the I-sync packet.

The PTM must generate the three synchronization packets in close succession, but they do not have to immediately follow each other. This means the PTM can delay the generation of any synchronization packet if the FIFO does not have enough space for the packet.

If the PTM receives a periodic synchronization request while trace is disabled because the TraceEnable signal is LOW, it delays synchronization until trace is re-enabled.

Forced overflow

If the PTM is servicing a periodic synchronization request, and receives a second periodic synchronization request from the same source, it immediately stops generating trace and drains the trace FIFO. This is described as a forced overflow.

When trace restarts, the PTM must generate the full periodic synchronization sequence. In this sequence, the I-sync packet indicates the overflow condition.

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