manual P&R need your help

[Altera_Forum]

Hi dears: 

 I designed 4 16bits adders, I want to use 4 adjacent LABs to implement these adders. I have assigned the positions for them as figure 1 shows. But the QII didn't fit according these assignments. And the fit reslut shows as figure 2.

[Altera_Forum]

--- Quote Start ---  Hi dears:  I designed 4 16bits adders, I want to use 4 adjacent LABs to implement these adders. I have assigned the positions for them as figure 1 shows. But the QII didn't fit according these assignments. And the fit reslut shows as figure 2.  --- Quote End ---   The simple design is shown like attached file.  There is a strange thing that QII report me only 58 LUTs being used.

[Altera_Forum]

A LAB has 10 LEs. 

But a 16 bit adder needs more than 10 LEs, it needs ~16 LEs.  Since Quartus can't fit the 4 adders into the 4 LABs you assigned, it's placing the remaining LEs in other LABs.  That said, why are you trying to manually assign the locations?

[Altera_Forum]

LABs have 16 LEs in Cyclone II to Cyclone IV, it's 10 LEs only in Cyclone. But this doesn't answer the question why.

[Altera_Forum]

Yes, 16 LEs in one LAB for CycloneII. 

I'm using EP2C5Q208C8. Actually, there are several 16 bits adder in my design, i want to place them in adjacent LABs.

[Altera_Forum]

Are there any warnings from Quartus saying why those modules weren't placed in the positions you wanted? Try to search with the name of the component or the location, if there are lots of warnings. 

As a side note, except in some extreme rare cases, you don't need to fix the locations of individual components in your designs. If you have specific timing requirements on some signals, then you should specify them as Timequest rules and let the fitter find the best placement for you. It can even be smarter than you in some cases ;)