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Overriding the max_transition parameter from .lib file in Innovus

anurans

Hi All,

How can I set a proper value for max_transition during PnR in Innovus ? Even if I use following commands (during MMMC analysis / OCV mode), Innovus seems to take the max_transition from the fast cell library (.lib) which I find too tight for lower frequencies. 

set_interactive_constraint_modes [all_constraint_modes -active]
set_max_transition 1.5 ${DESIGN_NAME} //1.5 in ns

Is there a way this can be done in the tool without touching library data ?

Thanks

  • Additional Information : I am using Innovus v16.22-s071_1 version. Even If I set this parameter in .sdc file, tool always seems to take the most pessimistic value from libs and sdc. Following command evidently suggests 

    report_constraint -drv_violation_type max_transition
    ###############################################################
    # Generated by: Cadence Innovus 16.22-s071_1
    # OS: Linux x86_64(Host ID xoc2.ewi.utwente.nl)
    # Generated on: Mon Jul 6 13:02:40 2020
    # Design: riscv_core
    # Command: report_constraint -drv_violation_type max_transition
    ###############################################################
    # format : frame 1 : split 1

    Check type : max_transition
    ---------------------------
    Pin : load_store_unit_i_data_sign_ext_q_reg_1_/CP View : data_gen_bc

    max_transition : 0.360
    - Transition Time: 0.366
    -----------------------------------------------------
    slack : -0.006 ( VIOLATED )

    it comes from the fast library specified in MMMC view. This is too tight for the design and I want to make it relaxed (i.e. 10% of clock period). Can someone shed light on fixing this ?

    Thanks

  • in reply to anurans

    I moved to the newer version of the tool (V19). Documentation says, following commands can override the max_transition value specified prior to this command.

     

    My commands go like :

    set_interactive_constraint_modes [all_constraint_modes -active]
    set_global timing_constraint_enable_drv_limit_override true
    set_max_transition 2.5 [current_design] -override

    But I still see the same max_transition value taken from .lib. Not the overridden one ! Can someone explain what is going wrong here ?

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