Chapter 4 PA-RISC Computer Systems - OpenPA.net

PA-RISC R&D Operating Systems Chorus
References
� HPBSD: Utah’s 4.3bsd port for HP9000 series machines 72 Original homepage of the HPBSD
project. Mike Hibler (July 1999: University of Utah. Accessed 4 October 2005)
3.7.9 Chorus
Architecture: Chorus/System V Unix (MiX)
Released: 1990 (development original project), 1991/92 (development follow-on)
Chorus was a micro-kernel (similar to Mach) based operating system, developed at INRIA in France 73
starting in 1979. A development effort was made to port Chorus to the PA-RISC architecture and
hardware in 1990-1991 at the Oregon Graduate Institute (OGI).
The porting effort, a funded research project lead by Jonathan Walpole 74 , was based on the Chorus v3.3
nucleus ( “kernel” ) with the Chorus/MiX v3.2 on it and targeted the then recent HP 9000/834 “workstation” (PA-
RISC 1.0 NS-1 processor). Hardware support was quite limited however, as apparently no network
interfaces or disk devices were supported and all console I/O depended on PDC and IODC (PA-
RISC “BIOS” ) routines. Code from various earlier projects were used, including source code from
HP-UX 2.0 and the HP Tut project (HP-UX on 2.0 Mach). The port succeeded up to the stage that
Unix shells and various system calls worked, but no access to file systems was possible.
A later porting project was started by Jon Inouye (also from Oregon Graduate Institute) to port the
Chorus/MiX v3.2 with the newer v3.4 nucleus to the PA-RISC 1.1 9000/720 workstation (which was
quite a popular target for OS/Unix porting efforts at that time). The port did not progress very far,
as it supported very few device drivers; it was apperently used for “virtual memory experiments.” In
contrast to the earlier (9000/834) port it used HP-UX 8.0 as a base.
Both ports were never distributed as they contained various copyrighted/licensed source code (from HP,
Chorus, USL, etc.).
Chorus/MiX in the version 3 was a complete System V Unix (both SVR32 and SVR4) compatible
distributed operating system, however based on micro-kernel and with additional real-time and multithreading
features. The system is divided into the nucleus which is the underlying operating system core
which “handles scheduling, memory management, real-time events, and communications.” The nucleus
is quite tiny ( “typically only 50 to 60 KB in size” ) and the only truly platform-dependent part of the
system. The rest of the operating system are implemented as servers (including device drivers, the Unix
environment, Unix job and memory control, network support and sockets, etc.) that sit on top of the
nucleus and communicate with each other and the kernel by passing messages. MiX is in this case a
group of subsystems/servers that implement the aforementioned System V compatible Unix on top of
the Chorus nucleus.
References
� Porting Chorus to the PA-RISC: Project Overview 75 (PDF, 0.1 MB) Walpole, Jonathan, et al. OGI
Technical Report No. CS/E-92-003 (January 1992: Oregon Graduate Institute)
72 http://www.cs.utah.edu/~mike/hpbsd/hpbsd.html
73 http://www.inria.fr/index.en.html
74 http://web.cecs.pdx.edu/~walpole
75 ftp://ftp.parisc-linux.org/docs/whitepapers/1992-chorus_reports/92-003.pdf
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