Area optimization in Quartus II

[Altera_Forum]

Hi, 

 Currently I have a complete synthesis report generated in Quartus II, which is optimzed for speed. I tried to do synthesis with Area optimzation. For that I took the 'Assignments -> settings -> Analysis& Synthesis settings -> Optimization technique'- to "Area". In the map report I can see that the mapping location changed in several places, but in the fit report the utilization is same as before. Can anybody confirm that this is an expected behavior or there is something wrong in my constraints giving.

[Altera_Forum]

Is it 100% identical, or just close? Look at LUTs/Regs, etc. It's possible it wasn't able to make much difference, although in general I usually see something. If it's identical, something is wrong. If I were to take a guess, open Design Partition Window and see what the top-level is set to. If it's post-fit strict(or Ignore changes to source files is checked, which is the option in Q10.0 I believe), then it would make sense that it ignores the synthesis changes. 

Also note that Quartus looks at timing constraints. So perhaps your design has really easy constraints, and so even though you're synthesizing for Speed, it may be doing a lot of Area opts. (I don't have a full handle on how timing-driven synthesis and the synthesis options work together).

[Altera_Forum]

Hi Rysc, 

Thanks for your information. The results were exactly same in that synthesis. I found there is one issue - the .qsf file was read only. I tried by channging the property of 'qsf' file by giving write permission. In the next synthesis the qsf file modified and the optimization technique changed to area. The result showed improvement and the logic utilization and ALUT usages were 5 to 10% less that the previous one.   Now I have a new question. Is there any parameter in quartus II by which we can ask the tool to optimized the area also when we give Optimization technique as Speed?

[Altera_Forum]

Ahhh. I thought a warning message popped up when you opened a project with a .qsf in read-only mode. But that certainly makes sense.  

It's obviously a trade-off, i.e. if you really need to optimize for speed to meet timing then you can't do area also. But you can make assignments on a hierarchical basis. So, for example, if your main setting is speed, go to a hierarchy you know meets timing and right-click -> Locate -> Assignment Editor. THe AE will come up with the hierarchy name at the top. Copy it into the To column, select the assignment Optimization Technique and set it to Area. Repeat as necessary. Also note that Balanced is a really good option. It's not a mid-way point, but often gets near the best of both. Basically it does the speed optimizations that don't have a significant impact on area, and does the area optimizations that don't have a significant impact on speed. Definitely worth a try.