2.7.6. Behavior of address comparators

Address comparator behavior depends on whether the comparator is used for TraceEnable, ViewData or events:

In these tables:

Fire

Means that the comparator matches for one cycle only.

Sticky, for data address comparators

Means that the comparator matches until a new data transfer occurs.

Sticky, for instruction address comparators

The meaning is implementation defined, but must be one of:

  • If the processor supports an independent Load/Store Unit (LSU) where data transfers can return out of order in relation to the instruction stream, then Sticky means that the comparator matches, and continues to match until the last executed data instruction completes. If there is no data instruction outstanding then the comparator matches until the end of the current instruction.

  • If the processor returns all data transfers in-order in relation to the instruction stream, then Sticky means that the comparator matches up to, but not including, the next instruction.

Table 2.5. Context-dependent behavior of single address comparators

Comparator typeExact Match bit [a]Event resourceTraceEnable
Instruction address0FireFire
Instruction address1FireFire
Data address0FireFire
Data address1FireFire

Table 2.6. Context-dependent behavior of address range comparators, from ETMv3.3

Comparator typeExact Match bit [a]Event resourceTraceEnable
Instruction address0StickySticky
Instruction address1FireFire
Data address0StickySticky
Data address1FireFire

Table 2.7. Context-dependent behavior of address range comparators, before ETMv3.3

Comparator typeExact Match bit [a]Event resourceTraceEnable
Instruction address0StickySticky
Instruction address1implementation defined [b]implementation defined [b]
Data address0StickySticky
Data address1implementation defined [b]implementation defined [b]

[b] In ETMv3.2 and earlier, the typical implementation defined behavior is Sticky.


Note

  • As Table 2.5, Table 2.6, and Table 2.7 show:

    • The TraceEnable and the Event resource outputs of a comparator always behave in the same way.

    • For the address range comparators, from ETMv3.3, as Table 2.6 shows:

          when the exact match bit is set to 1 the comparator output behavior is always Fire

          when the exact match bit is set to 0 the comparator output behavior is always Sticky.

  • Rules for the transition of TraceEnable describes the restrictions on when TraceEnable can transition.

  • Operation of ViewData describes how the comparators affect ViewData operation.

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