Altera HardCopy II Clock Uncertainty Calculator - Manual (Page 13)

Altera Corporation 1–7
August 2007 HardCopy II Clock Uncertainty Calculator User Guide
About HardCopy II Clock Uncertainty Calculator
calculators require the PLL settings summary file,
pll_settings_summary.txt
, as input data to calculate the clock uncertainty
values.
Clock Uncertainty Calculator
The clock uncertainty calculator is on the second worksheet. It operates
with a single green button and supports all designs, except designs with
a cascading PLL structure. When the clock uncertainty values are
calculated, they are displayed on the spreadsheet, and simultaneously
written to a text file, CU_Values.txt. The clock uncertainty values are for
worst-case scenarios, and account for I/O buffer noise, clock network
noise, core noise, PLL jitter, and static phase error.
Advanced Clock Uncertainty Calculator
The advanced clock uncertainty calculator is different than the clock
uncertainty calculator. The clock uncertainty values from the advanced
clock uncertainty calculator are considered more precise than the clock
uncertainty calculator, because it accounts for each dedicated PLL’s
utilization within the design. The advanced clock uncertainty calculator
requires the input of PLLs’ indices for both the source and destination
clock. Therefore, entering the PLLs’ indices on the advanced clock
uncertainty calculator should be relied on for both the PLL_Names.txt file
and the clock transfer report to generate the clock uncertainty values.
Also, you should use this calculator if there are cascading PLLs in the
design. After clock uncertainty calculation, the clock uncertainty values
are displayed on the spreadsheet and written to a text file,
CU_Advanced_Values.txt
.
Both the advanced clock uncertainty and clock uncertainty calculators
can calculate and display the setup and hold uncertainty results for
different types of clock transfers. You can apply these clock uncertainty
constraints to model jitter and noise to ensure integrity with clock signals.
When a clock uncertainty constraint exists for a clock signal, the
TimeQuest Timing Analyzer performs the most conservative setup and
hold checks. For a clock setup check, the setup uncertainty is subtracted
from the data time requirement. For the clock hold check, the hold
uncertainty is added to the data time requirement.
Figure 1–7 on page 1–8
shows examples of clock sources with a clock setup uncertainty applied
and clock sources with clock hold uncertainty applied.