FABulous Configuration Variables

FABulous can use environment variables to configure options, paths and projects. We distinguish between two types of environment variables: global and project specific environment variables.

• Global environment variables are used to configure FABulous itself. They always start with FAB_.

• Project specific environment variables are used to configure a specific FABulous project. They always start with FAB_PROJ_.

All environment variables can be set in the shell before running FABulous or can be set via .env files.

.env File Locations

Scope	Location	How to use
User global	~/.config/FABulous/.env	Created automatically or manually
Global (explicit)	Any path	Pass via --globalDotEnv CLI argument
Project (auto-detected)	<project_dir>/.FABulous/.env	Placed inside your project
Project (explicit)	Any path	Pass via --projectDotEnv CLI argument

Note

Environment variables set in the shell always have the highest priority, followed by project-specific .env files, then global .env files.

PDK Resolution Logic

FABulous uses three environment variables to locate and manage a Process Design Kit (PDK) for back-end GDS generation.

Variable	Purpose
FAB_PDK	Name of the PDK (e.g. ihp-sg13g2)
FAB_PDK_ROOT	File-system path to the PDK installation directory
FAB_PDK_HASH	Version hash identifying a specific PDK snapshot

Default value of FAB_PDK

When a new project is created with create_project, FAB_PDK is set to ihp-sg13g2 in the project .env file by default. This value can be overridden afterward.

Resolution at startup

When FABulous loads its settings, the following rules determine how the PDK is resolved. For ciel-supported PDKs, FABulous handles installation and activation automatically, so there is no need to manually run ciel enable.

1. Neither FAB_PDK nor FAB_PDK_ROOT is set. A warning is logged and GDS features are unavailable.

2. FAB_PDK_ROOT is set but FAB_PDK is missing. An error is raised asking the user to set FAB_PDK.

3. FAB_PDK is set without FAB_PDK_ROOT, and the PDK belongs to a ciel-supported family. FAB_PDK_ROOT is automatically resolved from the ciel home directory and the PDK is installed and activated via ciel.

4. FAB_PDK is set without FAB_PDK_ROOT, and the PDK is not ciel-supported. An error is raised asking the user to set FAB_PDK_ROOT manually.

5. Both are set, but the PDK is not a ciel family. FABulous assumes a custom PDK with manual setup. The path must exist on disk.

6. Both are set and the PDK is a ciel family. The recommended FAB_PDK_HASH is resolved from librelane. If the user did not provide FAB_PDK_HASH, it is filled in automatically; if the user-provided value differs from the recommended one, a mismatch warning is logged. The PDK is then installed and activated via ciel.

Global Environment Variables

Variable	Environment Variable	Type	Default	User Value	Description
user_config_dir	FAB_USER_CONFIG_DIR	Path	(dynamic)	/path/to/file	-
oss_cad_suite	FAB_OSS_CAD_SUITE	Path	None	/path/to/file	-
yosys_path	FAB_YOSYS_PATH	Path	yosys	/path/to/file	-
opensta_path	FAB_OPENSTA_PATH	Path	sta	/path/to/file	-
nextpnr_path	FAB_NEXTPNR_PATH	Path	nextpnr-generic	/path/to/file	-
iverilog_path	FAB_IVERILOG_PATH	Path	iverilog	/path/to/file	-
vvp_path	FAB_VVP_PATH	Path	vvp	/path/to/file	-
ghdl_path	FAB_GHDL_PATH	Path	ghdl	/path/to/file	-
klayout_path	FAB_KLAYOUT_PATH	Path	klayout	/path/to/file	-
openroad_path	FAB_OPENROAD_PATH	Path	openroad	/path/to/file	-
fabulator_root	FAB_FABULATOR_ROOT	Path	None	/path/to/file	-
models_pack	FAB_MODELS_PACK	Path	None	/path/to/file	-
switch_matrix_debug_signal	FAB_SWITCH_MATRIX_DEBUG_SIGNAL	bool	False	true / false	-
editor	FAB_EDITOR	str	None	any string	-
verbose	FAB_VERBOSE	int	0	1, 2	-
debug	FAB_DEBUG	bool	False	true / false	-
pdk_root	FAB_PDK_ROOT	Path	None	/path/to/file	Root directory of the PDK installation
pdk	FAB_PDK	str	None	any string	PDK name (e.g. ‘ihp-sg13g2’)
pdk_hash	FAB_PDK_HASH	str	None	any string	Specific PDK version hash; auto-resolved from librelane when omitted if the PDK is supported by ciel
fabric_die_area	FAB_FABRIC_DIE_AREA	tuple	(0, 0, 1000, 1000)	[0, 0, 1000, 1000]	-
windows_warning_acknowledged	FAB_WINDOWS_WARNING_ACKNOWLEDGED	bool	False	true / false	-

Project Specific Environment Variables

Variable	Environment Variable	Type	Default	User Value	Description
proj_dir	FAB_PROJ_DIR	Path	(dynamic)	/path/to/file	-
proj_lang	FAB_PROJ_LANG	HDLType	HDLType.VERILOG	verilog, vhdl, sv	-
proj_version_created	FAB_PROJ_VERSION_CREATED	Version	0.0.1	1.2.3	-
proj_version	FAB_PROJ_VERSION	Version	-	1.2.3	-

Interactive CLI Settables

These variables can be set and get interactively in the FABulous CLI using the set and get commands.

Usage:

FABulous> set <variable> <value>
FABulous> get <variable>

Variable	Type	Description
projectDir	Path	The directory of the project
csvFile	Path	The fabric file
verbose	bool	verbose output
force	bool	force execution