Description
Cyclone® IV GX devices have two types of PLLs - multi-purpose PLL (MPLL) and general-purpose PLL (GPLL). The Quartus® II software will automatically select the PLL type based on device usage and resources.
If you wish to specify a particular PLL for your design, you can use the Assignment Editor and add location assignments to your PLL instances. The syntax for the location value would be PLL_1, PLL_2, etc.
The .qsf syntax to assign a PLL instance to location PLL_1 is:
set_location_assignment PLL_1 -to "<instance name>:inst|altpll:altpll_component"
Resolution
Refer to Clock Networks and PLLs in Cyclone® IV Devices (PDF) to understand which PLL numbers correspond to MPLLs and GPLLs in your device.