data/markdown/OR_userguide/OR_odb_README.md

# OpenDB

OpenDB is a design database to support tools for physical chip design. It
was originally developed by Athena Design Systems. Nefelus, Inc. acquired
the rights to the code and open-sourced it with BSD-3 license in 2019 to support the DARPA
OpenROAD project.

The structure of OpenDB is based on the text file formats LEF
(library) and DEF (design) formats version 5.6.  OpenDB supports a
binary file format to save and load the design much faster than using
LEF and DEF.

OpenDB is written in C++ 98 with standard library style iterators.
The classes are designed to be fast enough to base an application on without
having to copy them into application-specific structures.


## Directory structure

```
include/odb/db.h - public header for all database classes
src/db - private/internal database representations
src/lefin - LEF reader
src/lefout - LEF writer
src/defin - DEF reader
src/defout - DEF writer
```

## Database API

We are still working on documenting the APIs.  We have over 1,800 objects
and functions that we are still documenting (for both TCL and Python).
**Contributions are very welcome in this effort**. Find starting points below.

### TCL

After building successfully, run OpenDB Tcl shell using
`../../build/src/odb/src/swig/tcl/odbtcl`. An example usage:

```
set db [dbDatabase_create]
set lef_parser [new_lefin $db true]
set tech [lefin_createTech $lef_parser ./src/odb/test/data/gscl45nm.lef]
```

You can find examples on using the API from Tcl under `test/tcl/` directory.

The full set of the Tcl commands exposed can be found under
`./build/src/swig/tcl/opendb_wrapper.cpp`. Search for `SWIG_prefix`.


### Python

After building successfully, run `openroad -python` to enable the Python
interpreter. You can find examples on using the API from Python under
`test/python/` directory.

To list the full set of the Python classes exposed run `openroad -python`
then:
```
import openroad
import odb
print(', '.join(dir(openroad)))
print(', '.join(dir(odb)))
```

### C++

All public database classes are defined in `db.h`. These class definitions
provide all functions for examining and modifying the database objects. The
database is an object itself, so multiple database objects can exist
simultaneously (no global state).

`dbTypes.h` defines types returned by database class member functions.

All database objects are in the `odb` namespace.

-   `dbChip`
-   `dbBlock`
-   `dbTech`
-   `dbLib`

All database objects have a 32bit object identifier accessed with the
`dbObject::getOID` base class member function that returns a `uint`. This
identifier is preserved across save/restores of the database so it should
be used to reference database object by data structures instead of pointers
if the reference lifetime is across database save/restores. OIDs allow the
database to have exactly the same layout across save/restores.

The database distance units are **nanometers** and use the type `uint`.

## Example scripts

## Regression tests

There are a set of regression tests in /test.

```
./test/regression-tcl.sh
./test/regression-py.sh
```

## Database Internals

The internal description included here is paraphrased from Lukas van Ginneken
by James Cherry.

The database separates the implementation from the interface, and as a result,
each class becomes two classes, a public one and a private one. For instance,
`dbInst` has the public API functions, while class `_dbInst` has the private
data fields.

The objects are allocated in dynamically resizable tables, the implementation
of which is in `dbTable.hpp`. Each table consists of a number of pages,
each containing 128 objects. The table contains the body of the `struct`,
not a set of pointers. This eliminates most of the pointer overhead while
iteration is accomplished by stepping through the table. Thus, grouping these
objects does not require a doubly-linked list and saves 16 bytes per object
(at the cost of some table overhead). Each object has an id, which is the
index into the table. The lowest 7 bits are the index in the page, while
the higher bits are the page number. Object id's are persistent when saving
and reading the data model to disk, even as pointer addresses may change.

Everything in the data model can be stored on disk and restored from disk
exactly the way it was. An extensive set of equality tests and diff functions
make it possible to check for even the smallest deviation. The capability
to save an exact copy of the state of the system makes it possible to create
a checkpoint. This is a necessary capability for debugging complex systems.

The code follows the definition of LEF and DEF closely and reflects many of
the idiosyncrasies of LEF and DEF. The code defines many types of objects
to reflect LEF and DEF constructs although it sometimes uses different
terminology, for instance, the object to represent a library cell is called
`dbMaster` while the LEF keyword is MACRO.

The data model supports the EEQ and LEQ keywords (i.e., electrically equivalent
and logically equivalent Masters), which could be useful for sizing. However,
it does not support any logic function representation. In general, there is
very limited support for synthesis-specific information: no way to represent
busses, no way to represent logic function, very limited understanding of
signal flow, limited support of timing information, and no support for high
level synthesis or test insertion.

The db represents routing as in DEF, representing a trace from point to point
with a given width. The layout for a net is stored in a class named `dbWire`
and it requires a special `dbWireDecoder` (which works like an iterator)
to unpack the data and another `dbWireEncoder` to pack it. The data model
does not support a region query and objects that are in the same layer are
scattered about the data model and are of different classes.

This means that whatever tool is using the layout information will have to
build its own data structures that are suitable to the layout operations
of that tool. For instance, the router, the extractor, and the DRC engine
would each have to build their unique data structures. This encourages
batch mode operation (route the whole chip, extract the whole chip, run
DRC on the whole chip).

## Limitations

## FAQs

Check out
[GitHub discussion](https://github.com/The-OpenROAD-Project/OpenROAD/discussions/categories/q-a?discussions_q=category%3AQ%26A+fastroute+in%3Atitle)
about this tool.


## LICENSE

BSD 3-Clause License. See [LICENSE](LICENSE) file.