Hi Geoffrey, What speed are you targetting? Virtex2 has embedded Multipliers Only. The add has to be in Fabric. The MAC will get inferred from your code and it should use whatever multiplier and adder resources it needs in the xc2v3000. The key will be your speed requirements - as that will determine whether or not you will need to use pipeline registers in fabric between the multiply and the final accumulator, as well as input/output registers.
There is a trade-off between speed and register usage.
A single clock cycle MAC in VirtexII is one end of the spectrum. At the other end in Virtex4 -12 with the built in input/output and mutiply pipeline registers you can get
500MHz operation in the DSP48 (which also has much lower power dissipation because of reduced fabric and routing usage).
- Vic