7.4.6. Data suppressed packet

If enabled, the ETM prevents the output of data trace when the number of free bytes in the FIFO drops below the level set in the ETMFFLR, register 0x00B, by activating the SuppressData signal. The following packet types are suppressed when SuppressData is asserted:

The first such data packet to be generated while data suppression is activated is replaced by a Data suppressed packet. Figure 7.36 shows a Data suppressed packet. Subsequent data packets are deleted entirely and generate no trace while data suppression is still active. Data suppression remains active until a data packet is generated while SuppressData is deasserted.

Figure 7.36. Data suppressed packet

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Data suppression does not occur and no Data suppressed packet is output if SuppressData is asserted and deasserted without the suppression of any data packets. This happens if the number of free bytes in the FIFO briefly drops below the FIFOFULL level during cycles when no data tracing occurs.

If data suppression occurs during a Data Instruction, data suppression must continue until the Data Instruction has completed. Because no Value not traced placeholder packets are output, and data tracing might not have started on the first transfer, it is not possible to determine which transfers in the Data Instruction were traced. As a result you might have to discard all transfers corresponding to the Data Instruction that were traced before the Data suppressed packet.

In ETMv3.2 and earlier, D-sync is required following a restart from data suppression. In other words, the first data address output must be a full 5-byte address. This resynchronization is not required in ETMv3.3 and later.

Synchronization is delayed while SuppressData is asserted. This applies to:

In rare cases this can cause an overflow. See Synchronization for more information.

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