timing budgeting flow

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2010 Renesas Mobile Corporation. All rights reserved.RENESAS Group CONFIDENTIAL

Timing Budgeting Flow


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What is Budgeting?

The process of distributing positive and negative slack and

creating block-level budget SDC files

Budgeter determines block input and output delays byanalyzing delays of inter block timing arcs

Budgeter does not modify timing, only distributes slacksamong blocks.


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What is Budgeting

Budgeting outputs all SDC constraints required to fully

describe the timing environment for blocks Delay setting for I/O(budget allocation) set_input_delay, set_output_delay

Load/drive setting for I/O set_load, set_drive,set_driving_cell

Operating condition setting set_operating_conditions

Timing exception setting set_false_path,set_multicycle_path, set_disable_timing

etc


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Achieve Accurate Budgeting

More accurate timing, more accurate I/O budgets Need timing

optimization

More accurate pin location, more accurate wire capacitanceestimation through I/O pins Need pin assignment

Better I/O budgets & wire capacitance, better SDC Ensure betterblock implementation

Easier to close top-level timing after implementing blocks

Quality of budgeting depends on quality of inputs


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Steps To Achieve Accurate Budgeting

Make timing more correlated to optimized design Placement &

legalization

Full-chip in place optimization

Assign pin locations to well estimate wire capacitance throughI/O pins for each block Plan group-aware global routing

Pin-cutting (pin assignment based on global route)

Pre-budgeting flow: complete all the above steps


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8/17 2010 Renesas Mobile Corporation. All rights reserved.RENESAS Group CONFIDENTIAL


Check timing environment check_timing Checkunconstrained paths report_timing Check timing is reasonable for budgeting

check_fp_timing_environment Check feasibility of thedesign and its timing constraints

Perform timing budgeting

allocate_fp_budgets Allocate budgets betweenblocks and create SDC for blocks

check_fp_budget_result Generate a report whichallows you to compare real delay with budgeted delay



Timing Budgeting Flow check_timing

Check unconstrained endpoints

All timing endpoints in the design should be constrained

If not, might be due to

SDC error: a clock definition is missing

or

Design error: some circuits are disconnected




report_timing

Check the most violating paths in the design Negativeslack in the design should be reasonable compared to theclock period (20% or less), or timing closure might not beachievable

Budgeter creates SDC with better quality if timing morecorrelates the final optimized implementation.



Timing Budgeting FlowAllocate Budgets

Allocate budgets Tcl command and partial list of options:

allocate_fp_budgets

[-black_box_cells bb_cells_list]

[-fixed_delay_objects objects_delay_list]

[-file_format_spec file_format_string][-no_interblock_logic] [-no_split]

[-cells budget_cell_names]

[-incremental] [-exploration]

[-create_qtm_models] [-qtm_model_path]

[-print_partial_constraints]

Check man page for detailed information



Budgeting Based On Crosstalk Effect

Do budgeting using noise-induced delay Timer will estimatecoupling effect based on congestion map

HierSi information will be written out on plan group pins

Store top-level xtalk effect for block implementationBudgeter will store effective aggressor driving strength for inputpins and coupling cap across block boundary into block CEL

view set budgeting_enable_hier_si true The variable is set to

true by default



Hierarchical Timing Closure



Timing Budgeting on ILM (Re-Budgeting)


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Timing Budgeting on ILM (Re-Budgeting)

After you generate the timing budgets using ILM models, the.CEL views of the associated soft macros are updatedautomatically to reflect the new interface path and blockinternal constraints. Note this does not work if you have

split library for the soft macro. All the blocks have to bein the same library as main library

To write out the complete ASCII sdc interface path andinternal block constraints file for the soft macros, open theassociated soft macro .CEL views and run the write_sdc

command.


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timing budgeting flow

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