Why do I get the error "Nios II generation failed, input clock is unknown or set to 0" in Qsys when generating my project in Linux?

Description

An issue has been identified in multi-user environments with the UniPHY DDR3 SDRAM controller in Qsys.  In an embedded system, this can result in error messages similar to the following:

• cpu: Nios II generation failed, input clock is unknown or set to 0

During generation, the Quartus® II software creates a directory "/tmp/compute_pll_temp" to hold temporary files regarding PLL calculations. However, this directory is not deleted on completion. The result is that if a different user then generates the core, permissions may prevent the PLL calculations being written.

Resolution

To work around this issue, users should delete the /tmp/compute_pll_temp directory after running the tool, or change permissions on the directory to allow all users write access.

This issue will be fixed in a future release of the Quartus II software.