Fast IO register constraints won't apply

[Altera_Forum]

Hi, 

 I have a SRAM memory interface in my design and I registered all the signals in a component called mem_ctrl. I set these registers as fast input/output registers in assignment editor. But I got a bounch of warnings like the following:  Warning: Can't pack node "mem_ctrl:COMP_MEM_CTRL|addr[0][0]" and I/O cell a_tap[0]. The node and I/O cell are connected across a Design Partition boundary.  And it takes almost 6.5ns for a signal going from its register to the pin according to the timing analyzer.  Should I put all those registers in the top level to apply fast IO register constraints? Or is there anything else I should pay attention to? (the mem_ctrl component is in the top partition, and I don't understand why the message said the signal needs to across partition boundary).  Your help is very much appreciated.  Hua

[Altera_Forum]

Have you applied the constraint to the pin of the top level or a signal lower down the hierarchy?

[Altera_Forum]

--- Quote Start ---  Have you applied the constraint to the pin of the top level or a signal lower down the hierarchy?  --- Quote End ---    Actually, I applied the constraints to both the pin and the register (in the component). Both of them got the warning message.

[Altera_Forum]

The constraint should be applied to the register, not to the pin, I think. At least I've been using the constraint succesfully in this way.

[Altera_Forum]

Applying to the pin shouldn't create this problem, should it? I will take it out anyway.

[Altera_Forum]

--- Quote Start ---  Warning: Can't pack node "mem_ctrl:COMP_MEM_CTRL|addr[0][0]" and I/O cell a_tap[0]. The node and I/O cell are connected across a Design Partition boundary.  (the mem_ctrl component is in the top partition, and I don't understand why the message said the signal needs to across partition boundary).  --- Quote End ---    It actually means the opposite. Because of the register packing and fast I/O assigment, they can't cross a partition.  Left click on the warning message and select "Help". Quartus will show a more detailed description of the warning, and will also point you to the relevant Handbook chapter that elaborates about the issue.

[Altera_Forum]

I know what you are saying, but what I meant was:  

 The mem_ctrl module is in the top partition, so the signal doesn't cross any partition boundary. I don't understand why the software think the node and the IO cell are connected across a Design Partition boundary.  Thanks anyway.

[Altera_Forum]

--- Quote Start ---  The mem_ctrl module is in the top partition, so the signal doesn't cross any partition boundary. I don't understand why the software think the node and the IO cell are connected across a Design Partition boundary.  --- Quote End ---    Again, please read the relevant handbook chapter pointed at the warning message help.   There are other reasons that might provoke this warning. e.g, the output enable of the signal can't cross a paritition boundary. Tapping might also restrict register packing.

[Altera_Forum]

Thanks vjAlter, I have read those chapters before I came here ...  

 After tried a few things, it seems that moving those registers from mem_ctrl module to the top level did help... verifying this right now.

[Altera_Forum]

--- Quote Start ---  Thanks vjAlter, I have read those chapters before I came here ...   --- Quote End ---    Ok. Sorry about insisting on that.  My point was to make sure you understand all the restriction on I/O register packing when using incremental compilation. And also that, as explained there, the message sometimes is misleading, and might be provoked by other restrictions, not exactly because the node and I/O cell are on different partitions.

[Altera_Forum]

None taken, vjAlter. 

 And yes, moving those registers to the top level did the trick. The register node and the IO buffer are in the same cell now.

[Altera_Forum]

It was actually because the signal was used in signal TAP. Removing them from the signal tap (moving those registers to the top level essentially did that) will fix the problem.