Relationally Placed Macros (RPMs)

The Xilinx libraries contain three types of elements.

• Primitives are basic logical elements such as AND2 and OR2 gates
  
  
• Soft macros are schematics made by combining primitives and sometimes other soft macros
  
  
• Relationally placed macros (RPMs) are soft macros that contain relative location constraint (RLOC) information, carry logic symbols, and FMAP/HMAP symbols, where appropriate
  
  

The last item mentioned above, RPMs, applies only to FPGA families.

The relationally placed macro (RPM) library uses RLOC constraints to define the order and structure of the underlying design primitives. Because these macros are built upon standard schematic parts, they do not have to be translated before simulation. The components that are implemented as RPMs are listed in the “Relationally Placed Macros” section of the “Selection Guide” chapter.

Designs created with RPMs can be functionally simulated. RPMs can, but need not, include all the following elements.

• FMAPs, HMAPs, and CLB-grouping attributes to control mapping. FMAPs and HMAPs have pin-lock attributes, which allow better control over routing. FMAPs and HMAPs are described in the “Mapping Constraint Examples” section.
  
  
• Relative location (RLOC) constraints to provide placement structure. They allow positioning of elements relative to each other. They are discussed in the “Benefits and Limitations of RLOC Constraints” section.
  
  
• Carry logic primitive symbols. Carry logic is discussed in the “Carry Logic in XC4000 and Spartans” section.
  
  

The RPM library offers the functionality and precision of the hard macro library with added flexibility. You can optimize RPMs and merge other logic within them. The elements in the RPM library allow you to access carry logic easily and to control mapping and block placement. Because RPMs are a superset of ordinary macros, you can design them in the normal design entry environment. They can include any primitive logic. The macro logic is fully visible to you and can be easily back-annotated with timing information.