Mapping synthesis/backend Critical Path to RTL.

Hi,

do you know if DC allows you to find the RTL segments that synthesize into the critical path?

I am not talking just about the start-stop registers of the path, but also the RTL that synthesizes into the combinational gates that comprise the critical path.

Ideally also with the state of the RTL inputs, plus the event that triggers the critical path.

E.g. if the critical path is invoked by an adder (between A register and Sum register):

Sum <= A XOR B;

I would like the tool to report that this is the line of RTL that is synthesized to the gates that comprise the critical path. And even better that the critical event would be when e.g. B=1 (state), and A changes from 0->1 (event).
Of course in a real case it would need to point to dozens of code lines in several different RTL files.

If not DC, does any synthesis or backend tool support something like that?

Thanks,
George

This is a new feature in I-version of DC.

I haven't used it on my own, but you should be able to judge which part of the RTL are on critical path by the hierarchy and register naming, as long as the path is not very very long.

Hi kbill,

Thanks I ll check the new DC version, I haven t found anything on its tool-commands guide though.

Unfortunately the critical path is several dozens of gates long, so there is a lot of logic between the two registers and it would be nice to report automatically the RTL, instead of manually backtracing each time.

Rgds,
George

kbill said:

This is a new feature in I-version of DC.

I haven't used it on my own, but you should be able to judge which part of the RTL are on critical path by the hierarchy and register naming, as long as the path is not very very long.

Click to expand...

this is usually required and really helps improve productivity while debugging.
I would select a product more on how debuggable it is

The one that tops the list is
Mentor's RealTime - its give cross probing from RTL, Netlist, Schematic to Physical
Cadence RTl Compiler - RT - Schematic to Physical Probing

Your request is more precise to to line number but the above will point you to line in the RTL code that inferenced the specific logic that is in the critical path

Hi Kbill. What is this I-version of DC u are talking about?

Well when you report your path from flop to flop, you could also report the net and also the hierarchical pins which help to find the logic.

In the past, the magma synthesize tool could generate a first netlist which indicate in comment which line of which rtl file generate the logic.

@rca

i think current tools atleast RC (Cadence) and RT(MENT) still do that instead of showing line number they directly take you to the RTL file and the line in code which causes the inference of that logic.

But this feature have primarily seen as beneficial only to STA and RTL folks or synthesis / implementation users can use it to provide feedback; obviously they are not given the liberty to change the RTL file.