This tutorial provides a brief overview of how to use TCL commands within OpenROAD Flow Scripts. You’ll learn how to set up your environment, use basic TCL commands, and integrate them into OpenROAD Flow Scripts. Let’s get started!
To begin using TCL with OpenROAD, ensure you have the OpenROAD tools installed. Once installed, you can access the TCL shell by running the OpenROAD executable:
$ openroad
OpenROAD v2.0-22053-g4e2370113b
Features included (+) or not (-): +GPU +GUI +Python : DEBUG
This program is licensed under the BSD-3 license. See the LICENSE file for details.
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TCL, or Tool Command Language, is a scripting language commonly used in electronic design automation. Here are some basic TCL commands you should know:
set: Assigns a value to a variable.puts: Outputs a string to the console.expr: Evaluates an expression.proc: Defines a procedure to encapsulate reusable code blocks.foreach: Iterates over each element in a list.Example:
set a 10
set b 20
puts "The sum is: [expr $a + $b]"
Example:
set my_list [list 1 2 3 4 5]
foreach item $my_list {
puts "Item: $item"
}
proc): Create a procedure to encapsulate reusable code blocks.Example:
proc greet {name greeting} {
set msg "$greeting, $name!"
return $msg
}
set message [greet "OpenROAD" "Hello"]
puts "Returned message: $message"
To use TCL commands in OpenROAD Flow Scripts, you can embed your TCL code directly into the scripts. The OpenROAD environment provides various commands specific to design, such as loading design files, running synthesis, and checking timing.
Example:
read_lef my_design.lef
read_def my_design.def
read_liberty my_design.lib
check_timing
An example design is provided in ordb/final.tar.gz that you can extract with:
tar xvf ordb/final.tar.gz
Then you can run the following TCL commands to load the design and libraries:
set odb_file "final/odb/spm.odb"
set def_file "final/def/spm.def"
set lef_files {"/home/mrg/.volare/sky130A/libs.ref/sky130_fd_sc_hd/techlef/sky130_fd_sc_hd__nom.tlef"
"/home/mrg/.volare/sky130A/libs.ref/sky130_fd_sc_hd/lef/sky130_fd_sc_hd.lef"}
set lib_files {"/home/mrg/.volare/sky130A/libs.ref/sky130_fd_sc_hd/lib/sky130_fd_sc_hd__tt_025C_1v80.lib"}
foreach lef_file $lef_files {
read_lef $lef_file
}
foreach lib_file $lib_files {
read_liberty $lib_file
}
read_def $def_file
There are a lot of files to load, so you can use the ORFS scripts to load all of the design configuration files.
get_cells command to retrieve all the cells (gates) in the design.Iterate over each cell using a loop to access its properties.
Example:
set cells [get_cells]
foreach cell $cells {
# Get the cell name
set cell_name [get_property $cell full_name]
puts "Cell: $cell_name"
}
get_nets command to retrieve all the nets in the design.Iterate over each net to access its properties.
Example:
set nets [get_nets]
foreach net $nets {
# Get the net name
set net_name [get_property $net full_name]
puts "Net: $net_name"
}
Use commands like report_timing to extract detailed timing information.
Example:
set path [lindex [find_timing_paths -sort_by_slack -group_count 1] 0]
set slack [get_property $path slack]
puts "Critical Path Slack: $slack"
Utilize get_property to fetch various attributes of cells, nets, or paths.
Example:
set cell [get_cells -name my_cell]
set cell_type [get_property $cell type]
puts "Cell Type: $cell_type"
These examples demonstrate typical usage patterns for iterating and querying within a design in OpenROAD using TCL commands. These scripts can be adjusted according to specific needs, leveraging the extensive set of commands available in the OpenROAD TCL API.
The flow scripts for the ORFS flow are in the directory flow/scripts.
There are many good examples of TCL usage in these scripts.
For example, the IO placement script is flow/scripts/io_placement.tcl and
is repeated here:
source $::env(SCRIPTS_DIR)/load.tcl
erase_non_stage_variables place
if {![env_var_exists_and_non_empty FLOORPLAN_DEF] && \
![env_var_exists_and_non_empty FOOTPRINT] && \
![env_var_exists_and_non_empty FOOTPRINT_TCL]} {
load_design 3_1_place_gp_skip_io.odb 2_floorplan.sdc
log_cmd place_pins \
-hor_layers $::env(IO_PLACER_H) \
-ver_layers $::env(IO_PLACER_V) \
{*}$::env(PLACE_PINS_ARGS)
write_db $::env(RESULTS_DIR)/3_2_place_iop.odb
write_pin_placement $::env(RESULTS_DIR)/3_2_place_iop.tcl
} else {
log_cmd exec cp $::env(RESULTS_DIR)/3_1_place_gp_skip_io.odb $::env(RESULTS_DIR)/3_2_place_iop.odb
}
This sources the load.tcl script, runs load_design (after checking
for some variables) and then runs the place_pins command to do IO
placement. Finally, it saves the design and pin placement with write_db
and write_pin_placement, respectively. If else condition skips placement
and just copies the ODB file. Presumably the IO placement will be done with
standard cell placemen tin the next step. The log_cmd is a TCL procedure
that ensures the command output gets put in the log.
Other interesting step scripts: global_place, resize (the timing optimizer), detail_place, cts, global_route, detailed_route, etc.
More information on TCL commands for timing can be found in the STA Tutorial.
Using TCL within OpenROAD Flow Scripts can greatly enhance your ability to automate and control the design process. For more information on TCL scripting, refer to the OpenROAD documentation.
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