Intel® Quartus® Prime Pro Edition User Guide: Timing Analyzer

ID 683243
Date 4/03/2023
Document Table of Contents Deriving PLL Clocks

The Derive PLL Clocks (derive_pll_clocks) constraint automatically creates clocks for each output of any PLL in your design. derive_pll_clocks detects your current PLL settings and automatically creates generated clocks on the outputs of every PLL by calling the create_generated_clock command.
Note: Only Intel® Arria® 10 and Intel® Cyclone® 10 GX devices support the Derive PLL Clocks (derive_pll_clocks) constraint. For all other supported devices, the Timing Analyzer automatically derives PLL clocks from constraints bound to the related IP.

Create Base Clock for PLL input Clock Ports

If your design contains transceivers, LVDS transmitters, or LVDS receivers, use the derive_pll_clocks to constrain this logic in your design and create timing exceptions for those blocks.

create_clock -period 10.0 -name fpga_sys_clk [get_ports fpga_sys_clk]

Include the derive_pll_clocks command in your .sdc file after any create_clock command. Each time the Timing Analyzer reads the .sdc file, the appropriate generated clock is created for each PLL output clock pin. If a clock exists on a PLL output before running derive_pll_clocks, the pre-existing clock has precedence, and an auto-generated clock is not created for that PLL output.

The following shows a simple PLL design with a register-to-register path:

Figure 102. Simple PLL Design

The Timing Analyzer generates messages like the following example when you use the derive_pll_clocks command to constrain the PLL.

derive_pll_clocks Command Messages

Info: Deriving PLL Clocks:
Info: create_generated_clock -source pll_inst|altpll_component|pll|inclk[0] -divide_by 2 -name
pll_inst|altpll_component|pll|clk[0] pll_inst|altpll_component|pll|clk[0]

The input clock pin of the PLL is the node pll_inst|altpll_component|pll|inclk[0] which is the -source option. The name of the output clock of the PLL is the PLL output clock node, pll_inst|altpll_component|pll|clk[0].

If the PLL is in clock switchover mode, multiple clocks generate for the output clock of the PLL; one for the primary input clock (for example, inclk[0]), and one for the secondary input clock (for example, inclk[1]). Create exclusive clock groups for the primary and secondary output clocks since they are not active simultaneously.

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