Project Oberon 2013 on RISC-V

This respository contains everything necessary to create a working RISC-V image of Project Oberon 2013, including a working RV32IM compiler as well as a port of Oberon itself.

Contents

• Runtime/ RISC5 emulator and operating system interface.
• Oberon/ Unmodified source code from Project Oberon 2013.
• OberonRV/ RISC-V modified source code.
• Norebo/ Norebo-specific and new modules.
• Bootstrap/ Pre-compiled modules to bootstrap Norebo.

How to run Oberon on RISC-V

If you don't want to figure out how to build an image, and you just want to try this out, clone the repository for the RISC-V Oberon emulator instead, as it includes an example RISC-V image.

How to build an image

To build a RISC-V image, simply run:

make imagerv

This will deposit a disk image: imagebuild/Oberon.dsk. This can be used for the emulator.

If you wish more control over the process, here is how to generate one with a different manifest, from whichever folder you prefer:

rm -rf imagebuild
./build-image.py -r OberonRV/Oberon -m manifests/manifest.csv

The -r flag specifies the creation of a RISC-V image. By default, build-image will select the manifests/manifest.csv manifest; but there are a few other manifests in that folder, and you can use a -m flag to specify using them instead. Editing the manifest to include whichever files you wish to include should be fairly straight-forward; just remember to add the corresponding .Mod files in the OberonRV/Oberon folder. You can specify a different folder than OberonRV/Oberon, but an unedited PO2013 repository will not work without some significant changes.

How to change the bootloader

The bootloader is embedded in the emulator. Thus, changing it is a separate process from building the image. You probably don't need to change the bootloader, but if you desire to:

• Compile your bootloader using the RISC-V compiler. To make this easier for yourself, running cd OberonRV; source functions.sh will source the roc and nor commands. You can then run roc BootLoad.mod, and the compiled program can be found in BootLoad.rsc.
• Use ORX.Mod in andreaspirklbauer's Oberon-building-tools, included as a submodule, to write a file that can be used as bootloader: nor ORX.WriteFile BootLoad.rsc BootLoad.code. BootLoad.code now contains a list of RISC-V instructions.
• Currently, the emulator won't understand this format. You need to add 0x to the start of every line, and a comma to the end. You can look at src/emu/bootloader.inc in the emulator for an example of the formatting. (I use vim to do this, and that's quick enough that I never bothered to write a script for it. So, this part is left as an exercise to the reader.) Then, replace bootloader.inc with your own bootloader.

TODO

• Test it on an FPGA; should be doable
• Support REALs and interrupts
• 64-bit support. This is rather easy, as to my knowledge it only requires minor changes.
• Bootstrap Norebo using a RISC-V emulator rather than RISC-5

Known Bugs

• For some reason, the compiler incorrectly reads symbol tables within Project Oberon. It reads parameter lengths of 0FFFFFFFFH as 07FH; probably due to reading only a byte instead of the full word. Currently, there is a workaround in the parser that allows parameter lengths of 07FH to be treated the same as 0FFFFFFFFH.

Credits

Several open-source projects were used to create this port.

• Of course, Project Oberon itself.
• sam-falvo's Oberon-RV compiler, of which this repository is a fork. It could compile many programs, but had bugs that prevented it from being able to compile the full Oberon system. I've patched most of these, such that it is now self-compiling. Some modules, such as RVAssem, RVDis, and RVOTool, remain either entirely or mostly unchanged.
• pdewacht's Project Norebo, used to create the RISC-V image, of which this repository is also a fork.
• pdewacht's Oberon emulator, used to emulate the created images. My port of the emulator to RISC-V can be found here.
• andreaspirklbauer's Oberon-building-tools, which is included as a submodule of this repository. The documentation on Oberon's boot process is very useful, as is the tooling.