Design constraints

• Constraining designs:

– constraints are means of communicating our requirements to the synthesis and back-end tools.

• Categories of constraints are :

– Timing constraints.

• maximum frequency
• duty cycle
• input delays
• output delays

– Layout constraints

• Avoid over-constraining the design

• Consequences of over-constraining are:

– Design performance suffers:

• critical timing paths get the best placement and fastest routing options.

• As the number of critical paths increase , the ability to obtain the design performance objectives decrease.

– Run times increase.

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