Cortex-A8 R2P2.pdf - ARM Information Center

Embedded Trace Macrocell14.6 Exact match bitYou can set the exact match bit in the address comparators to 1, to cause the ETM towait before permitting the address comparator to match. Setting the exact match bitprevents it from an unintentional match. The exact match bit behaves as follows in theETM:• Address comparators configured for instruction addresses• Address comparators configured for data addresses• Address range comparators.14.6.1 Address comparators configured for instruction addressesIf the exact match bit is set to 1, each instruction matches if both of the following aretrue:• the instruction matches the address comparison conditions• the instruction is not followed by a cancelling exception.To determine whether the instruction is followed by a cancellation exception, the matchdoes not take place until the next instruction. Therefore, matches do not occur in timeto control tracing, but instructions that are cancelled by exceptions do not cause thecomparator to match. This is useful when, for example, you want to count the numberof times an instruction has been executed.If the exact match bit is cleared to 0, each instruction matches if it matches the addresscomparison conditions. The match occurs at the time the instruction is traced andtherefore, cannot consider if the instruction is subsequently cancelled. This is usefulwhen you want to use the comparator to control tracing.NoteInstructions that are cancelled by exceptions do not cause the comparator to match. Thisis useful when you want to count the number of times an instruction has been executed.14.6.2 Address comparators configured for data addressesThe exact match bit does not affect whether a match occurs on a data address.14.6.3 Address range comparatorsIf an address range comparator configured for instruction address matches on aninstruction address, it continues to match until the next instruction addresses. If anaddress range comparator configured for data addresses matches on a data address, itcontinues to match until the next data addresses. This enables the use of address range14-26 Copyright © 2006-2008 ARM Limited. All rights reserved. ARM DDI 0344E