RAM and ROM may be specified in multiple ways. Each has advantages and disadvantages.
- Inference
Advantages:
- Highly portable
- Easy to read and understand
- Self-documenting
- Fast simulation
Disadvantages:
- Might not have access to all RAM configurations available
- Might produce less optimal results
Because inference usually gives good results, it is the recommended method, unless a given use is not supported, or it is not producing adequate results in achievable clock frequency, area, or power. In that case, explore other methods.
When inferring RAM, Xilinx recommends that you use the HDL Templates provided in the Vivado tools. As mentioned earlier, using asynchronous reset impacts RAM inference, and should be avoided.
-
Xilinx Parameterizable Macros (XPMs)
Advantages:
- Portable between Xilinx device families
- Fast simulation
- Support for asymmetric width
- Predictable quality of results (QoR)
Disadvantages:
- Limited to supported XPM options
XPMs are built on inference using fixed templates that you cannot modify. Therefore, they can guarantee QoR and can support features that standard inference does not. When standard inference does not support the features required, Xilinx recommends you use XPMs instead.
Note: When you compile simulation libraries usingcompile_simlib
, XPMs are automatically compiled. For more information, see the Vivado Design Suite User Guide: Logic Simulation (UG900). - Direct Instantiation of RAM Primitives
Advantages:
- Highest level control over implementation
- Access to all capabilities of the block
Disadvantages:
- Less portable code
- Wordier and more difficult to understand functionality and intent
- Core from IP catalog
Advantages:
- Generally more optimized result when using multiple components
- Simple to specify and configure
Disadvantages:
- Less portable code
- Core management