Quartus II Settings File Reference Manual - Altera

Chapter 4: Analysis & Synthesis Assignments 4–13
ALLOW_SHIFT_REGISTER_MERGING_ACROSS_HIERARCHIES
ALLOW_SHIFT_REGISTER_MERGING_ACROSS_HIERARCHIES
Type
Allows the Compiler to take shift registers from different hierarchies of your design
and place the shift registers in the same RAM.
Merging shift registers across hierarchies is good for logic utilization, as it allows
more shift registers to be put in RAM, and it allows the different shift registers to
share the same external counter logic. However, merging shift registers across
hierarchies can be bad for timing as it pulls together registers from different unrelated
hierarchies.
When this option is set to Auto, the Compiler decides whether it wants to merge shift
registers across hierarchies based on resource availability, timing and the
Optimization Technique setting. When the option is set to On, shift registers are
merged across hierarchies as much as possible. When the option is set to Off, shift
registers are not be merged across hierarchies at all. This option is ignored when the
Auto Shift Register Replacement setting is set to Off.
This option can be used as a project-wide option, or assigned to a design entity.
This option is turned on by default.
Enumeration
■ Always
■ Auto
■ Off
Device Support
You can use this setting in projects targeting the following device families:
■ Arria GX
■ Arria II GX
■ Arria II GZ
■ Arria V
■ Cyclone
■ Cyclone II
■ Cyclone III
■ Cyclone III LS
■ Cyclone IV E
■ Cyclone IV GX
■ Cyclone V
■ HardCopy II
■ HardCopy III
■ HardCopy IV
June 2012 Altera Corporation Quartus Settings File
Reference Manual