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Open-Source Flight Operating Systems



What is the status of thinking of open-source operating
systems for microsat flight computers?

First, having looked at this a bit, it appears to me that
the state of real-time operating systems (RTOSs) in general
and open-source RTOSs in general is something of a mess.
As far as I can tell, the use of home-grown RTOSs is still
widespread, and no single solution dominates either the
proprietary or open-source markets for RTOSs.  It seems
that folks would like to move away from home-grown
RTOSs.  If you believe the press reports,  there is a lot
of interest in moving to Real-Time Linux (RTLinux).
My personal suspicion is that this a case of Linux-fever
that has not yet been tempered by real-world experience.  It
appears that RTLinux is not nearly mature as [traditional]
Linux.  Furthermore, RTLinux is big.  Real-time capabilities
were added to Linux by developing a small real-time kernel
that sits between the hardware and a traditional Linux
kernel.  Interrupts not processed by the small, real-time
kernel are passed to the [big] traditional Linux kernel.
I doubt that this is the sort of solution that is going to
be useful in something like a 1 MB machine, although I
haven't yet tried to load RTLinux into a PC-class machine.

However, it appears that all is not lost.  It seems to me that
RTEMS (http://www.rtems.com) is an interesting candidate
for an open-source RTEMS for microsats.  I believe that
it can be configured with a fairly small footprint.  I
installed RTEMS for i386s Friday and compiled a simple
test program that was included (the "Hello World" sort of
thing).  The program could drive a CRT and talk to the
keyboard.  It wasn't very big; it fit on a diskette.
Unfortunately, the diskette is at work, so I can't look
at the size...

Has anyone looked at using RTEMS in microsats?  I don't
believe that an 80186 port exists, but the person who
seems to be the main RTEMS guy thinks that it
wouldn't be a difficult port.  Of course, RTEMS undoubtedly
doesn't contain an AX.25 driver [insert long tirade about
utility of moving beyond AX.25 for microsat command and
control here...].  On the other hand, it does support
a POSIX-like API, which might permit spacecraft software
to be developed and debugged under UNIX and then ported
to RTEMS.

Is anyone looking at open-source RTOSs for the RUDAK and
SpaceQuest FCV-53 flight computers?

Has anyone looked at RTEMS for microsats?

Would a RTEMS port to the 80186 be of any use?

Would anyone actually run RTEMS if it were available?
Perhaps, on one of the RUDAKs?

-tjs
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