2.7.2. Comparator access size field behavior, in ETMv3.1 and later

Behavior of the size field in ETMv3.1 and later depends on the type of comparison, and is described in the following sections:

Note

Single address comparators configured for data addresses

The access size field enables any access to any byte in the selected byte, halfword or word to cause the comparator to match. This behavior is required to perform reliable address comparisons on unaligned accesses.

Figure 2.14 shows how this can be used.

Figure 2.14. Single address comparisons in ETMv3.1 and later

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For more information about the behavior of data value comparators see Operation of data value comparators

Single address comparators configured for instruction addresses

Instruction address comparators ignore the access size field, and the address must match exactly. However, the size field must still be set to the expected instruction set to help some ETMs adapt to matching instructions in different states.

Address range comparators configured for data addresses

In ETMv3.1 and later, range comparators ignore the value of the access size field.

The address range comparator matches if any of the accessed bytes fall in the defined range. Figure 2.15 shows an example of this.

Figure 2.15. Range comparisons in ETMv3.1 and later

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Address range comparators configured for instruction addresses

The address range comparator matches if the first byte of the instruction falls in the range. Although the access size field is ignored, it must still be set to the expected instruction set to help some ETMs adapt to matching instructions in different states.

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