Abstract:
Current versions of Designer timing analysis software do not automatically notify the analyst of asynchronous feedback loops in their design. These warning were the default for earlier versions such as ALS 2.3.2. This checking can be done as described below.
To make DTAnalyze issue a warning if it senses an asynchronous loop perform the following operation. Under the Options menu, use the Set command to set the variable "showbreakloop" to "1" (without the quotation marks). The Set command setting can be verified by using the Get command, also under the Options menu, which will print the "showbreakloop" variable's value in the main status window. Now, when a timing analysis is performed, a warning should appear in the main status window indicating any asynchronous loops and which pins were put into a break set
Here's sample output from a simple design using cross-coupled NAND gates to make an RS flip-flop.
Variable
showbreakloop = 1
; Pins 'G2:A' has been put into STOP set to break loop.
Thanks to Anita Jeong of Actel for providing this work around.
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