How to reduce LAB usage in MAX II devices?

[Altera_Forum]

I'm currently using MAX II - EPM1270T144 device while the fitter says it requires 128 LABs to implement the project, but the device contains only 127 LABs. But i noticed the LE(logic element) usage has been only 479/1270 (38%) 

 I'm designing everything in block-diagram files, it contains many shift registers though, and i've tried removing some of them well it still can't reduce the LAB usage!   I wonder what could be possiblly consuming so many LABs?

[Altera_Forum]

--- Quote Start ---  I wonder what could be possiblly consuming so many LABs?  --- Quote End ---  This can't be answered without analyzing your design in detail. However, the Quartus tool is optimizing rather effectivly, in general. So a pessimistic assumption would be: The design is too complex. In some cases, resource consuming structures, e.g. parallel dividers, may be replaced by slower serial designs.

[Altera_Forum]

I've openned the chip planner and discovered many LABs only have one LE occupied within them. why couldn't these LEs be used?

[Altera_Forum]

Look at the control signals (reset, clock, etc). 

 This sort of thinkg happen a lot if the tool needs to place logic into cells with disjoint control signals.  Changing your coding style with things like ripple counters to things that use one clock and clock enable functions may help.  Too many clocks can also get you.

[Altera_Forum]

Thank you Avatar, that was helpful.  

 So am i correct to say, that one LAB (containing 10 LEs) only has one set of Async Clear, Preset or Clock signal, LEs using different Async Clear, Preset or Clock signal cannot be packed into the same LAB. Am i correct?    Because i use lots of different Async signals in my design, (they're all described in schmetics) and so i see many LEs cannot be packed into others within the same LAB.

[Altera_Forum]

You should look in the MAX II Users Guide. 

http://www.altera.com/literature/hb/max2/max2_mii51002.pdf Look at LAB control signals for some clarity.  In some cases it is one, in other cases it iw two. ASYNC signals are a challenge. Try to get things into a SYNC mode, and control stuff with CE controls if possible.