Multicycle path constraint apply scenario?

[ranbarasan]

I have some idea about what is meant by multicycle path.but i need to know actually i need the usage scenario. actually mcp is to avoid the violations. but can we appy mcp to the paths wherever violations occur in the path? obviously the ans is nooooooo. so wat will be disadvantages of mcp???

Plz send me the ans..

Thanks in advance.

 

[TrickyDicky]

if you have a path where two registers use the same clock enable that is a periodic clock enable, then you know that the setup and hold time can be much longer for these registers as they really only get updated once every N clocks.

 

[ads-ee]

See this pdf on multicycle paths https://www.ee.bgu.ac.il/~digivlsi/slides/Multicycles_6_2.pdf.

Basically multicycle paths are useful if you have a large combinational circuit that has a propagation delay that exceeds the clock period and you either can't (e.g. encrypted IP core) or don't want to pipeline the circuit (someone else's code or they wanted the design finished last week) and you can allow the circuit to run slower at some multiple of the clock period, then using the aforementioned enable along with a multicycle path will allow you to implement the design and meet timing.

 

[vGoodtimes]

The main disadvantage of the MCP is that you must verify that the constraint is applicable and remains applicable after any design change. This limits the places where MCPs can be used.

 

[ThisIsNotSam]

I have some idea about what is meant by multicycle path.but i need to know actually i need the usage scenario. actually mcp is to avoid the violations. but can we appy mcp to the paths wherever violations occur in the path? obviously the ans is nooooooo. so wat will be disadvantages of mcp???

Plz send me the ans..

Thanks in advance.

MCP is not used to avoid violations blindly. careful with what you wish for. you should work very closely with the designer to figure out if the path can actually be made a MCP.

 

[slutarius]

MCP has no disavantage itself.

MCP is not intended to avoid violation. It actually is a correct representation to the behavior of design logic.
If the designer make constraint by himself, it is easy for him to know where should need the MCP constraint from begining.
In case you are not awared of all logic behavior of a design, you need to consult its designer to check whether a specific path can be set as MCP or not, and how many cycles are correct..

You are not allowed to set the MCP just because the paths are timing violated !!