6.2.1. ATREADYS and ATVALIDM

The ATREADYS to the original trace source can only be asserted when both of the trace outputs have accepted the current packet. One or both connected trace sinks might be disabled. If so, they must tie ATREADYS HIGH.

Because the trace sinks accept the trace data at different moments, the ATVALIDM signal to them is not asserted immediately after they have read the data packet because the data packet must persist for the other trace sink. The ATVALIDM signal is valid only for new packets until a valid ATREADYM cycle is seen. If ATVALIDM is incorrectly asserted when an old data value is still present then this might cause a packet duplication to appear in the trace stream for that source. This is highly likely to create problems at decompression.

Devices that connect to the output of the Replicator, the TPIU and the ETB for example, must tie the ATREADYM signal HIGH when they are disabled. If connected devices do not do this they cause the trace stream to stop the other channel that might still be enabled. This removes the requirement for the replicator to be aware of the state of downstream components

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