what is the difference between inferring and instantiating

[samcheetah]

what is the difference between inferring a block RAM and instantiating a block RAM. what i have understood is that instantiating something means that you have to tell the synthesizer that i want such and such thing like a RAMB16 etc. whereas if you declare a reg like

reg [3:0] abc [3:0];

this is inferring block RAM.

so why are there two ways? and which one is better

 

[echo47]

To "instantiate RAM" means to explicitly put a RAMB* library module into your HDL. Refer to your "Libraries Guide" chapter "Design Elements" section "RAMB16_*".

To "infer RAM" means to create an HDL register array that the compiler automatically recognizes as a RAMB* block. Refer to your "XST User Guide" chapter "HDL Coding Techniques" section "RAMs/ROMs".

I prefer inferring everything possible, because that makes my HDL code more portable, and it greatly speeds up behavioral simulation. However, some FPGA features cannot be inferred, so then I must instantiate.

 

[kumar_eee]

Re: what is the difference between inferring and instantiati

Instantiation:
Instantiation allows one module to incorporate a copy of another module into itself.

Inferring:
Inferring means all the resources are available in the chip itself, in your design u r going to use that resource...