Using XC9500 Local Function Block Feedback
All macrocells in XC9500 devices communicate globally through the FastCONNECT.
There is also a local feedback path between all macrocells in the same
function block that can be used for speed critical paths. You may want to use local
feedback if you have critical paths that have multi-level logic, or need to
reduce your feedback delay between a group of registers that can fit in one function
block.
Note: The local feedback cannot be used in XC9500XL and XC9500XV because the architectures do
not support it.
The local feedback path will be used when it is required to meet a timing
constraint, provided the fitter can group the required logic functions into the
same function block. The local feedback path will also be used when you have
manually grouped logic functions together in the same function block with a special form of the LOC attribute, provided the Use Local Macrocell Feedback option is enabled in the Implementation Options menu of the Design Manager, or, in the Process Properties menu of the Project Navigator.
Speeding up tCO
Speeding up fMAX
Speeding up tSU