From OR1K

The aim of this project is to develop and maintain an OpenRISC 1000 architectural simulator which acts as the functional golden reference for HDL implementations.



Or1ksim is a generic OpenRISC 1000 architecture simulator capable of emulating OpenRISC based computer systems at the instruction level. It includes models of a range of peripherals, allowing complete systems to be modelled.

Key features

Or1ksim provides a range of features:

  • Free, open source code, which can be used as a standalone simulator, or as a library.
  • High level, fast, architecture simulation that allows early code analysis and system performance evaluation.
  • Models of all major OpenCores peripheral and system controller cores and easy addition of new peripheral models.
  • Easy configuration for different environments (memory configurations and sizes, OR1K processor model, configuration of peripheral devices).
  • Remote debugging via TCP/IP with the GNU Debugger (GDB) using either the GDB Remote Serial Protocol or through a modeled JTAG interface.
  • A library interface allowing simple OSCI TLM 2.0 SystemC integration.


Or1ksim maintains a Stable release, recommended for general use, and a Development release, available through SVN.

Stable release

The latest stable version, 0.4.0, was released in June 2010 after 15 months of new development. This release of Or1ksim matches current OpenRISC Reference Plaform SoC definition, including the OpenRISC 1200 version 2 procesor.

A compressed tar image of the Or1ksim 0.4.0 release is available on the download page.

New features

The following features are new in this release.

  • A full DejaGNU base regression test suite with 2,499 tests of the standalone simulator and library.
  • A library interface modeling the JTAG debug interface. This will enable a GDB interface to the library version of Or1ksim via JTAG.
  • Single precision floating point instructions (implemented by JungSook Yang).
  • A configuration option, allowing l.xori to treat its operand as unsigned. Note. Using this option will require changes to the GCC compiler to generate valid code.

The debug interface to the standalone simulator is compatible with GDB 6.8 for OpenRISC 1000 using the GDB Remote Serial Protocol. See the tool chain page for further details.

Or1ksim 0.4.0 introduces a new interface to the library, which models the JTAG interface to the OpenRISC debug unit. This is intended for use with transactional models of the debug interface, and is currently the only way to connect a debugger to the Or1ksim library.

Note. When used as a library, only a single instance of Or1ksim may be used, due to widespread use of static and global variables in the code. Remedying this limitation is a long term objective of the project.

Deprecated features

For backwards compatibility, the old OpenRISC JTAG interface to GDB continues to be supported. However this interface is now deprecated and will be discontinued in the next release. All new applications should use the GDB Remote Serial Protocol. If a JTAG interface to standalone Or1ksim is required that should be implemented via a GDB RSP server.

Missing features

The following are not yet supported in Or1ksim

  • 64-bit instructions (ORBIS64)
  • double precision floating point instructions (ORFPX32/ORFPX64)
  • vector instructions (ORVDX64)
  • GDB Remote Serial Protocol interface to the Or1ksim library.

Tested host platforms

The current stable version has been tested under Fedora 11 Linux and Ubuntu 10.04 Linux.

Development release

You may checkout the latest version of Or1ksim from SVN using:

svn co

Note. The checkout process may take a while. The current top of SVN tree is not considered stable, but should always build correctly.

New features

The latest version, which in time will become release 0.5.2 adds the following features:

  • Support for GDB 7.2
  • IEEE 754 (2008) compliant single precision floating point.
  • A direct GDB Remote Serial Protocol interface to the library version of Or1ksim.
  • Extended library interface, so Or1ksim can be used as a built-in simulator with GDB.
  • An improved parser for configuration files, although it currently cannot handle ATA disc specifications.
  • An up to date commented reference configuration file in the distribution.

Features removed

The following feature is obsolete and dropped as planned.

  • Support for the OpenRISC JTAG GDB interface (replaced by RSP)

Features for future addition

The following other features are being considered for inclusion in future releases.

  • Support for multiple instances (Stefan Wallentowitz).
  • Adding double precision floating point support. This is only feasible if a 64-bit version is also developed.
  • Letting memory blocks identify using their "name" field.
  • Fix the memory controller component and get its tests working in the regression suite.

Features for future removal

Some features of the current Or1ksim appear incomplete or obsolete. The following features are being considered for removal.

  • stall and unstall commands in the CLI.
  • The custom unit compiler.
  • Dynamic execution (a build option, not completed)

Users are encouraged to suggest other features via the OpenRISC forum or through the OpenRISC bug tracker.

SystemC TLM 2.0 interface for Or1ksim

A demonstration wrapper has been developed by Embecosm to provide an OSCI SystemC TLM 2.0 interface to Or1ksim. This comprises both an application note and reference software.

Robert Guenzel's [ application note] mentioned above has extensive discussion of the SystemC TLM 2.0 version. He makes some important suggestions for improving performance.

Multiple instantiations of Ork1sim

Or1ksim can be used as a library as well as a standalone program. However, because the code makes heavy use of global variables, only one instance can ever be present. This is very inconvenient for those wishing to model a multi-core system.

Stefan Wallentowitz has implemented a prototype version of Ork1sim, based on the stable Or1ksim 0.3.0 release, which fixes this problem.

A full description and the source code as a patch for Or1ksim 0.3.0 is currently available from


The installation instructions are the same for both stable and development releases. Or1ksim is always built from source - there are no binary distributions.

Installation under Linux/Cygwin

First download the sources either from the download page or from SVN and unpack if necessary. The following instructions assume the unpacked source is in directory or1ksim-0.4.0, and the code is to be installed in /opt/or1ksim. Build and install Or1ksim as follows.

mkdir builddir_or1ksim
cd builddir_or1ksim
../configure --target=or32-elf --prefix=/opt/or1ksim
make all
make install
export PATH=/opt/or1ksim/bin:$PATH

If DejaGNU and the OpenRISC GNU tool chain are installed, the build can be tested as follows.

make check

All tests should past. Any failures should be reported, with as much detail as possible using the OpenRISC bug tracker.

Note. If you want to compile with optimization disabled which make gdb debugging easier, please configure with following command which instructed by Jeremy Bennett.

../or1ksim-0.4.0/configure --target=or32-elf --prefix=/opt/or1ksim CFLAGS="-O0 -DINLINE=static -DNO_SOFTFLOAT_UNUSED" 

Or1ksim can also be installed using the OpenRISC toolchain installation script (a more automated installation), which is available from the GNU Toolchain page.

Note. This script is currently awaiting update to use the latest stable version. At present it will install the previous stable version.

More detailed information on installing Or1ksim (and the rest of the OpenRISC 1000 tool chain) with examples of the simulator in use may be found in Embecosm Application Note EAN2: The OpenCores OpenRISC 1000 Simulator and Tool Chain: Installation Guide.

Installation on Mac OS X

The current stable build, Or1ksim 0.4.0, incorporates patches from Mark Jarvin, so that it should build on Mac OS X (Snow Leopard).

Robert Guenzel has provided an application note on building the previous stable release, Or1ksim 0.3.0, for Mac OS 10.4: . This may be of interest to Mac users.


Or1ksim includes a User Guide. This provides information on using and configurating Or1ksim, both as a standalone tool and as a library. It also gives some guidance on the internal structure of Or1ksim. It is available in PDF on the download page.

The documentation can also be generated from the source to give HTML, info, DVI and PostScript.

The code is documented to take advantage of the Doxygen documentation system, which provides automatically generated, structured documentation on the files, functions and data-structures of the entire program, together with their interrelationships.

Documentation would benefit from extending, particularly with tutorial material and with more detail on the internals of the program (see Contributing, below).


A summary of the command options can be seen with

or32-elf-sim --help

For booting Linux, use the sim.cfg file in the root directory of the Linux distribution with the command

or32-elf-sim -f arch/openrisc/or1ksim.cfg vmlinux

More details on Linux for OpenRISC 1000 may be found on the operating systems page.

Embecosm Application Note EAN2 described in the Installation section above includes examples using Or1ksim. The User Guide for the OpenRISC 1000 port of GDB 6.8 includes details of running Or1ksim with GDB.

To aid in debugging, the immediate field of a NOP can be used to control some simulation parameters. The following table defines the meaning of each NOP field. These are defined in or1ksim/cpu/or1k/spr-defs.h. They are documented in the latest user guide with the distribution.

Name Value Description
NOP_NOP 0x0000 Normal nop instruction
NOP_EXIT 0x0001 End of simulation
NOP_REPORT 0x0002 Simple report
NOP_PRINTF 0x0003 Simprintf instruction (obsolete)
NOP_PUTC 0x0004 Simputc instruction
NOP_CNT_RESET 0x0005 Reset statistics counters
NOP_GET_TICKS 0x0006 Get # ticks running
NOP_GET_PS 0x0007 picosecs/cycle
NOP_TRACE_ON 0x0008 Turn on tracing
NOP_TRACE_OFF 0x0009 Turn off tracing
NOP_RANDOM 0x000a Return 4 random bytes
NOP_OR1KSIM 0x000b Return non-zero if this is Or1ksim

Note. This list is not definitive. See the User Guide for an up to date list.

Discussion Forum

Or1ksim is discussed within the OpenRISC Forum and on IRC at, channel #opencores. All users are encouraged to contribute suggestions and advice.


We are constantly looking for developers to help in the development of the simulator, though you don't need to be a highly skilled developer to do so. Many (very useful) projects may be performed without any C programming knowledge or without an intricate knowledge of the openrisc architecture.

What is needed

A few items to get you started.

  • Extend the documentation. Or1ksim now has a User Guide. However this would benefit from some good tutorial material. This is an excellent task for anyone new to or1ksim. This would involve the following.
    • Documenting, in the form of well narrated passages (not point form!), how to get started using Or1ksim, the general pitfalls that someone new to Or1ksim may take and how to avoid them.
    • Some neat examples of how to use some of the more "cool" peripherals of the sim (esp. how to make use of the Ethernet peripheral).
    • Documenting the interface that is used to implement the peripherals.
    • Documenting the more arcane features of the simulator, including the various execution models, branch prediction, super scaler emulation and in general what they are useful for.
If you have any questions about the above, don't hesitate to contact us on the mailing list.
  • Improve the testsuite. We now have a proper test suite, based on the old tests and with a set of new tests for the Or1ksim library interface. But it is far from complete.
    • A number of the old tests build, but don't run correctly, since they need VAPI to drive their inputs. Fixing this would allow the UART and GPIO tests to be added.
    • There is an attempt at a comprehensive test of the integer instruction set, but it does not compile correctly. Fixing this would be valuable.
    • Many of the existing tests of peripherals are crude. In particular, the Ethernet could benefit from a robust set of tests.
  • Test or1ksim on non-Linux platforms (various UNIX and Cygwin platforms). The developers do not have acess to every operating system out there. We would like the simulator to run on as many platforms as possible. Mark Jarvin already provides valuable help by running the code on Mac OS X.
If you are running on anything other than Linux you would help us a great deal if you could periodically check if the simulator builds (and works) on your prefered platform, reporting any failures to the mailing list.
  • Add additional models of OpenCores peripherals and system controllers. Only a small subset of the great number of peripherals available at opencores are currently modeled. Some examples of peripherals to write a model for might have been suggested.
    • WishBone Real Time Clock.
    • IrDA communication core.
    • USB 2.0 function core.
    • Most things that connect to the WishBone bus. A good list may be found here.
  • Add a new feature. The section on the development release above lists several new features. Coders wishing to help are very welcome.

If you have a suggestion that you'd like to see developed, feel free to add it to Buzilla or start a discussion on the OpenRISC forum or the developer mailing lists.

How to submit a contribution

The up to date details may be found in the MAINTAINERS file at the top level of the Or1ksim source tree.

The submission process uses the OpenRISC mailing lists, in preference to the OpenRISC forum. Cross post to both the and lists, since they have disjoint sets of readers.

SVN HEAD and release branches

For changes to SVN HEAD or release branches, this is the process in summary.

  • submit your patch as a diff against the current SVN HEAD (put the patch inline, not as an attachment, to make it easy for users to read in mail clients).
  • wait for reviews, modify and repost as necessary.
  • if approved by a maintainer, the patch will be applied by one of the Or1ksim maintainers (see the MAINTAINERS file).

If you are making regular contributions, please ask to be given SVN write access, by posting to the mailing lists. This will give you the ability to commit changes, and you will be listed in the MAINTAINERS file. You should still follow the same process of submitting to the mailing list, and waiting for reviews and approval.

Private branches

If you wish to make major changes, you should obtain write-after-approval permission as above and create your own branch. List the branch in the MAINTAINERS file, with yourself as owner. You may make any changes you like to this branch, without reference to the mailing lists (although the community would love to hear about your progress).

When the time comes to merge your work into SVN HEAD or a release branch, follow the process for SVN HEAD and release branches.

Obvious patches

Obvious patches (for example trivial typos) may be fixed by anyone with write-after-approval permission. Such changes should be posted after the even to both mailing lists.


The team currently working on or1ksim:

An important input to the current stable release has been Waqas Ahmed's Master's dissertation at the Royal Institute of Technology, Sweden, Implementation and Verification of a CPU Subsystem for Multimode RF Transceivers. His work identified a large number of bugs in Or1ksim, which have been fixed (and tested) in this release. Waqas has kindly made his dissertation available on the download page.

Past Contributors

These are the people who are currently not working on the or1ksim, but have contributed in significant ways in the past:

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