2.10.2. ETMv3 behavior

In ETMv3.x, the trace port protocol enables the trace port to run at a different speed from that of the processor. Modes in these devices are port size invariant in that the number of pins in the trace port remains constant as the trace port bandwidth changes. The trace capture device is unaware of the mode in use.

In ETMv3.x, the trace is collected on both clock edges in all modes except dynamic mode. Dynamic mode is designed for capture on-chip using the ETM clock instead of TRACECLK.

The two fields used in ETMv1 and ETMv2 are combined into a single field, bits [13, 17:16], Port mode[2:0], as Table 2.16 shows.

Table 2.16. Port mode, port speed and data pins in ETMv3

Port mode [2:0]NameTRACECLK edge

Clock ratio[a]

Data:Clock ratio[b]

Width ratio[c]

b000Dynamic, for capture on-chipNot used-1:11:1
b011implementation definedBoth-implementation defined1:1
b1001:1Both1:21:1, or asynchronous1:1

[a] Ratio of (Trace port clock speed):(ETM clock speed)

[b] Ratio of (Trace port data rate):(ETM clock speed)

[c] Ratio of (Number of Data port pins):(Number of ETM pins)

The implementation defined encoding is available for non-standard ratios, such as 2:3.

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