Altera CRC Compiler - Manual (Page 10)

1–6 Chapter 1: About This Compiler
Installation and Licensing
CRC Compiler User Guide © November 2009 Altera Corporation
Preliminary
All megafunctions in a device time out simultaneously when the most restrictive
evaluation time is reached. If there is more than one megafunction in a design, a
specific megafunction’s time-out behavior may be masked by the time-out behavior of
the other megafunctions.
1 For MegaCore functions, the untethered timeout is 1 hour; the tethered timeout value
is indefinite.
Your design stops working after the evaluation time expires; the checksum output
signal in a generator and the crcbad output signal in a checker are forced low.