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Combinational Loops generated in RTL Compiler

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seanigang

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rtlcompiler delete_unloaded_seqs

Hi! During synthesis using RTL Compiler, combinational loops were found in my design. As what the log file says, the tool disabled them, deleted several hierarchical instances, then added loop breakers. I've simulated the generated netlist and found errors on the output waveform. Now, my questions are :

-What happens to the actual hardware/schematic when these combinational loops were disabled? Does the tool deletes signals,modules,instances included in the combinational loop?

-Any tips on how to make these things right?


Any help is deeply appreciated. TIA
 

rtl compiler set_attr

Hi Seanigang,
Combinational loops are broken by adding buffers with broken arc (i/p to o/p). It is done for timing purpose. RTL complier timing engine will does insert comb. loop breakers.

There is not relationship with Comb. loop breaker with deletion of instance/signal/module.

To control the deletion of instance pls use following attribute

set_attr delete_unloaded_ins false /
set_attr delete_unloaded_seqs false /

Thanks
Aravind
 

Halo,

Sorry for bumping this old thread. I have a question regarding the buffer that you spoke of here, which will break a combinational loop.
Is this a special type of buffer or will any buffer do the job?

Thank you!
 

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