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Altera_Forum
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13 years ago

Fmax and Restricted Max

Hello, In the Time Quest, the Fmax for my design is 303 MHz , but the Restricted Fmax is 250 MHz with a Note that says 'limit due to minimum period restriction (max I/O toggle rate)' . The clo...
Altera_Forum's avatar
Altera_Forum
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12 years ago

Restricted Fmax comes into play when using things like DSP and memory blocks. the timing paths inside of these blocks are not explicitly calculated using the formula that kaz lists above due to their complicated structure. instead, the datasheet specs of these blocks in their various modes are programmed into Quartus and will show up as Restricted Fmax

as others have pointed out, you'll need to look at the lower of these two numbers to see how fast your design will actually run. better yet, take a look at the Top Failing Paths or similar