-max_slew

Max slew value (in the current time unit) that the characterization will test. If this parameter is omitted, the code would use max slew value for specified buffer inbuf_list from liberty file.

-max_cap

Max capacitance value (in the current capacitance unit) that the characterization will test. If this parameter is omitted, the code would use max cap value for specified buffer inbuf_list from liberty file.

-slew_steps

Number of steps thatmax_slew will be divided into for characterization. The default value is12, and the allowed values are integers[0,MAX_INT].

-cap_steps

Number of steps thatmax_cap will be divided into for characterization. The default value is34, and the allowed values are integers[0,MAX_INT].

-buf_list

Tcl list of master cells (buffers) that will be considered when making the wire segments (e.g.{BUFXX,BUFYY}).

-root_buffer

The master cell of the buffer that serves as root for the clock tree. If this parameter is omitted, the first master cell from-buf_list is taken.

-wire_unit

Minimum unit distance between buffers for a specific wire. If this parameter is omitted, the code gets the value from ten times the height of-root_buffer.

-distance_between_buffers

Distance (in microns) between buffers thatcts should use when creating the tree. When using this parameter, the clock tree algorithm is simplified and only uses a fraction of the segments from the LUT.

-branching_point_buffers_distance

Distance (in microns) that a branch has to have in order for a buffer to be inserted on a branch end-point. This requires the-distance_between_buffers value to be set.

-clustering_exponent

Value that determines the power used on the difference between sink and means on the CKMeans clustering algorithm. The default value is4, and the allowed values are integers[0,MAX_INT].

-clustering_unbalance_ratio

Value determines each cluster’s maximum capacity during CKMeans. A value of0.5 (i.e., 50%) means that each cluster will have exactly half of all sinks for a specific region (half for each branch). The default value is0.6, and the allowed values are floats[0,1.0].

-sink_clustering_enable

Enables pre-clustering of sinks to create one level of sub-tree before building H-tree. Each cluster is driven by buffer which becomes end point of H-tree structure.

-sink_clustering_size

Specifies the maximum number of sinks per cluster for the register tree. The allowed values are integers[0,MAX_INT]. If this is not specified the size will be automatically chosen between10,20or30 based on the tree buffer max cap.

-sink_clustering_max_diameter

Specifies maximum diameter (in microns) of sink cluster for the register tree. The allowed values are integers[0,MAX_INT]. If this is not specified the diameter will be automatically chosen between50,100or200, based on the tree buffer max cap.

-macro_clustering_size

Specifies the maximum number of sinks per cluster for the macro tree. The default value is4, and the allowed values are integers[0,MAX_INT].

-macro_clustering_max_diameter

Specifies maximum diameter (in microns) of sink cluster for the macro tree. The default value is50, and the allowed values are integers[0,MAX_INT].

-balance_levels

Attempt to keep a similar number of levels in the clock tree across non-register cells (e.g., clock-gate or inverter). The default value isFalse, and the allowed values are bool.

-clk_nets

String containing the names of the clock roots. If this parameter is omitted,cts looks for the clock roots automatically.

-num_static_layers

Set the number of static layers. The default value is0, and the allowed values are integers[0,MAX_INT].

-sink_clustering_buffer

Set the sink clustering buffer(s) to be used.

-obstruction_aware

Enables obstruction-aware buffering such that clock buffers are not placed on top of blockages or hard macros. This option may reduce legalizer displacement, leading to better latency, skew or timing QoR. The default value isFalse, and the allowed values are bool.

-apply_ndr

Applies 2X spacing non-default rule to clock nets except leaf-level nets following some strategy. There are four strategy options:none,root_only,half,full. If this is not specified, the default value isnone.

-dont_use_dummy_load

Don’t apply dummy buffer or inverter cells at clock tree leaves to balance loads. The default values isFalse.

-sink_buffer_max_cap_derate

Use this option to control automatic buffer selection. To favor strong(weak) drive strength buffers use a small(large) value. The default value is0.01, meaning that buffers are selected by derating max cap limit by 0.01. The value of 1.0 means no derating of max cap limit.

-delay_buffer_derate

This option balances latencies between macro cells and registers by inserting delay buffers. The default value is1.0, meaning all needed delay buffers are inserted. A value of 0.5 means only half of necessary delay buffers are inserted. A value of 0.0 means no insertion of delay buffers.

-library

This option specifies the name of Liberty library from which clock buffers will be selected, such as the LVT or uLVT library. It is assumed that the library has already been loaded using the read_liberty command. If this option is not specified, clock buffers will be chosen from the currently loaded libraries, which may not include LVT or uLVT cells.

-repair_clock_nets

This option includes fixing long wires inside CTS prior to latency adjustment with delay buffers. This can lead to a more balanced clock tree. The default is not to perform clock net repair.

-no_insertion_delay

Ignore sink insertion delay in clock tree construction and balancing.

clkbuf_regs

Splitting registers from macros

clkload

Dummy loads to help balance the clock tree

delaybuf

Delay buffers to help balance the tree

-out_file

The file to savects reports. If this parameter is omitted, the report is streamed tostdout and not saved.

-apply_ndr

Applies 2X spacing non-default rule to clock nets except leaf-level nets following some strategy. There are four strategy options:none,root_only,half,full. If this is not specified, the default value isnone.

-buf_list

Tcl list of master cells (buffers) that will be considered when making the wire segments (e.g.{BUFXX,BUFYY}).

-branching_point_buffers_distance

Distance (in microns) that a branch has to have in order for a buffer to be inserted on a branch end-point. This requires the-distance_between_buffers value to be set.

-clustering_exponent

Value that determines the power used on the difference between sink and means on the CKMeans clustering algorithm. The default value is4, and the allowed values are integers[0,MAX_INT].

-clustering_unbalance_ratio

Value determines each cluster’s maximum capacity during CKMeans. A value of0.5 (i.e., 50%) means that each cluster will have exactly half of all sinks for a specific region (half for each branch). The default value is0.6, and the allowed values are floats[0,1.0].

-delay_buffer_derate

This option balances latencies between macro cells and registers by inserting delay buffers. The default value is1.0, meaning all needed delay buffers are inserted. A value of 0.5 means only half of necessary delay buffers are inserted. A value of 0.0 means no insertion of delay buffers.

-distance_between_buffers

Distance (in microns) between buffers thatcts should use when creating the tree. When using this parameter, the clock tree algorithm is simplified and only uses a fraction of the segments from the LUT.

-library

This option specifies the name of Liberty library from which clock buffers will be selected, such as the LVT or uLVT library. It is assumed that the library has already been loaded using the read_liberty command. If this option is not specified, clock buffers will be chosen from the currently loaded libraries, which may not include LVT or uLVT cells.

-macro_clustering_max_diameter

Specifies maximum diameter (in microns) of sink cluster for the macro tree. The default value is50, and the allowed values are integers[0,MAX_INT].

-macro_clustering_size

Specifies the maximum number of sinks per cluster for the macro tree. The default value is4, and the allowed values are integers[0,MAX_INT].

-num_static_layers

Set the number of static layers. The default value is0, and the allowed values are integers[0,MAX_INT].

-root_buffer

The master cell of the buffer that serves as root for the clock tree. If this parameter is omitted, the first master cell from-buf_list is taken.

-sink_buffer_max_cap_derate

Use this option to control automatic buffer selection. To favor strong(weak) drive strength buffers use a small(large) value. The default value is0.01, meaning that buffers are selected by derating max cap limit by 0.01. The value of 1.0 means no derating of max cap limit.

-sink_clustering_levels

…

-sink_clustering_max_diameter

Specifies maximum diameter (in microns) of sink cluster for the register tree. The allowed values are integers[0,MAX_INT]. If this is not specified the diameter will be automatically chosen between50,100or200, based on the tree buffer max cap.

-sink_clustering_size

Specifies the maximum number of sinks per cluster for the register tree. The allowed values are integers[0,MAX_INT]. If this is not specified the size will be automatically chosen between10,20or30 based on the tree buffer max cap.

-sink_clustering_levels

…

-skip_nets

Tcl list containing the clock nets to be skipped (e.g.{net1,net2}). If the net is a root clock net, the whole clock is skipped, otherwise only the subnet specified is skipped.

-wire_unit

Minimum unit distance between buffers for a specific wire. If this parameter is omitted, the code gets the value from ten times the height of-root_buffer.