EPXA4 Datasheet, PDF (15/34 Pages) Altera Corporation – Excalibur Devices

Errata Sheet - Appendix A
While most tools do not report when a full data address has been
output, if a data address differs from the previous data address traced
in bits [31:28], then a full data address would have been output,
allowing full data addresses that have not been periodically forced to
be detected by the user. When a full data address cannot be detected
in this way the user must either find the first data address that is at
least 1024 cycles after the first instruction traced following the
overflow, or treat all data addresses as invalid until the next gap in
the trace.
Workaround
This workaround is for tool vendors only and must be read in conjunction
with the Embedded Trace Macrocell Specification (ARM IHI 0014).
Development tool vendors can implement the above checks automatically
in the trace tools, so that all data given to the user is guaranteed to be
correct. In particular:
■ The target address of branches is always known, so the comparison
of the addresses before and after overflow can be accurate.
■ The tools must detect when invalid trace is caused by this erratum,
and not cause instruction trace to be lost as a result.
■ The tools can detect when the first instruction after overflow is an
indirect branch (traced with a PIPESTAT of BD) and not an SWPB
with a 16-bit trace port, and not treat the data trace as invalid unless
the branch address is earlier than expected. An SWPB cannot be
reliably detected in this way because of the 1-byte gap that is
sometimes left on a 16-bit trace port to align instruction addresses.
■ Where data addresses are invalid until the next synchronization
point, the tools should treat data addresses as valid following the next
5-byte data address output instead.
There is no known way to prevent the erratum from occurring, other than
increasing the amount of filtering performed, particularly by ViewData,
to reduce the chance of an overflow occurring.
Implications of workaround
In some circumstances substantial data trace, and in particular data
addresses, might be lost. Data might be treated as invalid when it is not,
particularly in systems where this erratum never or rarely occurs. As a
result, it is recommended that if the workaround is implemented it is
possible to turn it off.
Altera Corporation
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