EPXA4 Datasheet, PDF (18/34 Pages) Altera Corporation – Excalibur Devices

Errata Sheet - Appendix A
Conditions
The conditions under which this erratum occurs are not easily predicted.
It never occurs if the last executed instruction failed its condition codes.
Implications
The last instruction executed before an interrupt or prefetch abort might
be missing from the trace. Some tools always report the extra instruction
traced as having executed, in which case the user will instead see an extra
instruction reported before an interrupt or prefetch abort when this
erratum does not occur.
If tracing continues until after the exception handler returns, the user can
use the address of the first instruction executed upon returning from the
exception to determine the actual behavior.
Workaround for tools vendors
Since the execution status is unknown, development tools cannot reliably
report the last instruction executed before an abort or an interrupt.
The development tools must display the last instruction traced with its
execution status shown as ‘unknown’, rather than suppress it as defined
in the trace port protocol.
Implications of workaround
It is not possible to determine which instruction was executed
immediately before an interrupt or prefetch abort, without referring to the
last instruction traced before the interrupt.
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