Global Placement
The global placement module in OpenROAD (gpl) is based on the open-source
RePlAce tool, from the paper "Advancing Solution Quality and Routability Validation
in Global Placement".
Features:
- Analytic and nonlinear placement algorithm. Solves electrostatic force equations using Nesterov's method. (link)
- Verified with various commercial technologies and research enablements using OpenDB (7/14/16/28/45/55/65nm).
- Verified deterministic solution generation with various compilers and OS.
- Supports Mixed-size placement mode.
Commands
- Parameters in square brackets `[-param param]` are optional.
- Parameters without square brackets `-param2 param2` are required.
Global Placement
When using the -timing_driven flag, gpl does a virtual repair_design
to find slacks and
weight nets with low slack. It adjusts the worst slacks (modified with
-timing_driven_nets_percentage) using a multiplier (modified with
-timing_driven_net_weight_max). The multiplier
is scaled from the full value for the worst slack, to 1.0 at the
timing_driven_nets_percentage point. Use the set_wire_rc command to set
resistance and capacitance of estimated wires used for timing.
Routability-driven arguments
- They begin with
-routability. -routability_check_overflow,-routability_max_density,-routability_max_bloat_iter,-routability_max_inflation_iter,-routability_target_rc_metric,-routability_inflation_ratio_coef,-routability_max_inflation_ratio,-routability_rc_coefficients
Timing-driven arguments
- They begin with
-timing_driven. -timing_driven_net_reweight_overflow,-timing_driven_net_weight_max,-timing_driven_nets_percentage
global_placement
[-timing_driven]
[-routability_driven]
[-disable_timing_driven]
[-disable_routability_driven]
[-skip_initial_place]
[-incremental]
[-bin_grid_count grid_count]
[-density target_density]
[-init_density_penalty init_density_penalty]
[-init_wirelength_coef init_wirelength_coef]
[-min_phi_coef min_phi_conef]
[-max_phi_coef max_phi_coef]
[-reference_hpwl reference_hpwl]
[-overflow overflow]
[-initial_place_max_iter initial_place_max_iter]
[-initial_place_max_fanout initial_place_max_fanout]
[-pad_left pad_left]
[-pad_right pad_right]
[-force_cpu]
[-skip_io]
[-skip_nesterov_place]
[-routability_check_overflow routability_check_overflow]
[-routability_max_density routability_max_density]
[-routability_max_bloat_iter routability_max_bloat_iter]
[-routability_max_inflation_iter routability_max_inflation_iter]
[-routability_target_rc_metric routability_target_rc_metric]
[-routability_inflation_ratio_coef routability_inflation_ratio_coef]
[-routability_max_inflation_ratio routability_max_inflation_ratio]
[-routability_rc_coefficients routability_rc_coefficients]
[-timing_driven_net_reweight_overflow]
[-timing_driven_net_weight_max]
[-timing_driven_nets_percentage]
Options
| Switch Name | Description |
|---|---|
-timing_driven |
Enable timing-driven mode. See link for timing-specific arguments. |
-routability_driven |
Enable routability-driven mode. See link for routability-specific arguments. |
-skip_initial_place |
Skip the initial placement (Biconjugate gradient stabilized, or BiCGSTAB solving) before Nesterov placement. Initial placement improves HPWL by ~5% on large designs. Equivalent to -initial_place_max_iter 0. |
-incremental |
Enable the incremental global placement. Users would need to tune other parameters (e.g., init_density_penalty) with pre-placed solutions. |
-bin_grid_count |
Set bin grid's counts. The internal heuristic defines the default value. Allowed values are integers [64,128,256,512,...]. |
-density |
Set target density. The default value is 0.7 (i.e., 70%). Allowed values are floats [0, 1]. |
-init_density_penalty |
Set initial density penalty. The default value is 8e-5. Allowed values are floats [1e-6, 1e6]. |
-init_wirelength_coef |
Set initial wirelength coefficient. The default value is 0.25. Allowed values are floats. |
-min_phi_coef |
Set pcof_min ($\mu_k$ Lower Bound). The default value is 0.95. Allowed values are floats [0.95, 1.05]. |
-max_phi_coef |
Set pcof_max ($\mu_k$ Upper Bound). Default value is 1.05. Allowed values are [1.00-1.20, float]. |
-overflow |
Set target overflow for termination condition. The default value is 0.1. Allowed values are floats [0, 1]. |
-initial_place_max_iter |
Set maximum iterations in the initial place. The default value is 20. Allowed values are integers [0, MAX_INT]. |
-initial_place_max_fanout |
Set net escape condition in initial place when $fanout \geq initial_place_max_fanout$. The default value is 200. Allowed values are integers [1, MAX_INT]. |
-pad_left |
Set left padding in terms of number of sites. The default value is 0, and the allowed values are integers [1, MAX_INT] |
-pad_right |
Set right padding in terms of number of sites. The default value is 0, and the allowed values are integers [1, MAX_INT] |
-force_cpu |
Force to use the CPU solver even if the GPU is available. |
-skip_io |
Flag to ignore the IO ports when computing wirelength during placement. The default value is False, allowed values are boolean. |
Routability-Driven Arguments
| Switch Name | Description |
|---|---|
-routability_check_overflow |
Set overflow threshold for routability mode. The default value is 0.2, and the allowed values are floats [0, 1]. |
-routability_max_density |
Set density threshold for routability mode. The default value is 0.99, and the allowed values are floats [0, 1]. |
-routability_max_bloat_iter |
Set bloat iteration threshold for routability mode. The default value is 1, and the allowed values are integers [1, MAX_INT]. |
-routability_max_inflation_iter |
Set inflation iteration threshold for routability mode. The default value is 4, and the allowed values are integers [1, MAX_INT]. |
-routability_target_rc_metric |
Set target RC metric for routability mode. The default value is 1.25, and the allowed values are floats. |
-routability_inflation_ratio_coef |
Set inflation ratio coefficient for routability mode. The default value is 2.5, and the allowed values are floats. |
-routability_max_inflation_ratio |
Set inflation ratio threshold for routability mode. The default value is 2.5, and the allowed values are floats. |
-routability_rc_coefficients |
Set routability RC coefficients. It comes in the form of a Tcl List {k1, k2, k3, k4}. The default value for each coefficient is {1.0, 1.0, 0.0, 0.0} respectively, and the allowed values are floats. |
Timing-Driven Arguments
| Switch Name | Description |
|---|---|
-timing_driven_net_reweight_overflow |
Set overflow threshold for timing-driven net reweighting. Allowed value is a Tcl list of integers where each number is [0, 100]. |
-timing_driven_net_weight_max |
Set the multiplier for the most timing-critical nets. The default value is 1.9, and the allowed values are floats. |
-timing_driven_nets_percentage |
Set the reweighted percentage of nets in timing-driven mode. The default value is 10. Allowed values are floats [0, 100]. |
Cluster Flops
This command does flop clustering based on parameters.
cluster_flops
[-tray_weight tray_weight]\
[-timing_weight timing_weight]\
[-max_split_size max_split_size]\
[-num_paths num_paths]
Options
| Switch Name | Description |
|---|---|
-tray_weight |
Tray weight, default value is 20.0, type float. |
-timing_weight |
Timing weight, default value is 1.0, type float. |
-max_split_size |
Maximum split size, default value is -1, type int. |
-num_paths |
KIV, default value is 0, type int. |
Useful Developer Commands
If you are a developer, you might find these useful. More details can be found in the source file or the swig file.
# debugging global placement
global_placement_debug -pause -update -inst -draw_bins -initial
# adds padding and gets global placement uniform target density
get_global_placement_uniform_density -pad_left -pad_right
Example scripts demonstrating how to run gpl on a sample design on core01 as follows:
./test/core01.tcl
Regression tests
There are a set of regression tests in ./test. For more information, refer to this section.
Simply run the following script:
./test/regression
Limitations
Using the Python interface to gpl
This API tries to stay close to the API defined in C++ class Replace
that is located here.
When initializing a design, a sequence of Python commands might look like the following:
from openroad import Design, Tech
tech = Tech()
tech.readLef(...)
design = Design(tech)
design.readDef(...)
gpl = design.getReplace()
Here is an example of some options / configurations to the global placer. (See Replace.h for a complete list)
gpl.setInitialPlaceMaxIter(iter)
gpl.setSkipIoMode(skip_io)
gpl.setTimingDrivenMode(timing_driven)
gpl.setTimingNetWeightMax(weight)
There are some useful Python functions located in the file grt_aux.py but these are not considered a part of the final API and they may change.
FAQs
Check out GitHub discussion about this tool.
References
- C.-K. Cheng, A. B. Kahng, I. Kang and L. Wang, "RePlAce: Advancing Solution Quality and Routability Validation in Global Placement", IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, 38(9) (2019), pp. 1717-1730. (.pdf)
- J. Lu, P. Chen, C.-C. Chang, L. Sha, D. J.-H. Huang, C.-C. Teng and C.-K. Cheng, "ePlace: Electrostatics based Placement using Fast Fourier Transform and Nesterov's Method", ACM TODAES 20(2) (2015), article 17. (.pdf)
- J. Lu, H. Zhuang, P. Chen, H. Chang, C.-C. Chang, Y.-C. Wong, L. Sha, D. J.-H. Huang, Y. Luo, C.-C. Teng and C.-K. Cheng, "ePlace-MS: Electrostatics based Placement for Mixed-Size Circuits", IEEE TCAD 34(5) (2015), pp. 685-698. (.pdf)
- A. B. Kahng, J. Li and L. Wang,
"Improved Flop Tray-Based Design Implementation for Power Reduction",
IEEE/ACM ICCAD, 2016, pp. 20:1-20:8. - The timing-driven mode has been implemented by Mingyu Woo (only available in legacy repo in standalone branch.)
- The routability-driven mode has been implemented by Mingyu Woo.
- Timing-driven mode re-implementation is ongoing with the current clean-code structure.
Authors
- Authors/maintainer since Jan 2020: Mingyu Woo (Ph.D. Advisor: Andrew. B. Kahng)
- Original open-sourcing of RePlAce: August 2018, by Ilgweon Kang (Ph.D. Advisor: Chung-Kuan Cheng), Lutong Wang (Ph.D. Advisor: Andrew B. Kahng), and Mingyu Woo (Ph.D. Advisor: Andrew B. Kahng).
- Also thanks to Dr. Jingwei Lu for open-sourcing the previous ePlace-MS/ePlace project code.
License
BSD 3-Clause License. See LICENSE file.