EPXA4 Datasheet, PDF (16/34 Pages) Altera Corporation – Excalibur Devices

Errata Sheet - Appendix A
A.2.2
Execution status unknown prior to an interrupt or prefetch
abort—Category 2
Description
The trace port protocol allows for each instruction traced to be reported
with a corresponding branch address to indicate the address of the next
instruction. If this branch address is not output then the trace tools must
calculate the address of the next instruction. If a branch address is output
then the PIPESTAT pins of the trace port will indicate Branch Executed (BE)
or Branch with Data (BD).
When an interrupt or prefetch abort occurs, the instruction which follows
the last instruction to be executed should be traced (even though it did not
execute) with a branch address to the relevant exception vector. In the case
of interrupts this is often referred to as the interrupted instruction. The
trace tools must recognize that the branch was to an interrupt or prefetch
abort exception vector, and correctly treat that instruction as having not
executed. In this way, the trace can reliably indicate if the last instruction
executed failed its condition codes.
Sometimes the ETM does not trace this extra instruction but instead traces
the last instruction executed as having branched to the exception vector.
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