Notes from March 12 discussions:

J. Robnett suggests that we inquire whether OSs we are considering support
both IPv4 and IPv6.

Two types of security features are needed.  First the OS itself needs 
security so that an interloper cannot use the RTOS to find a way into
the systems which declare it a trusted system.  Second, there must
be security that we provide ourselves to prevent somebody from hijacking
the VLA and turning it to his own usages.

The OS footprint is a consideration we should add to the things we want to
know about the OS.

K. Ryan reported briefly on the JBed OS.  It is a small, java oriented, RTOS.
RT features are mainly that it supports tasks, with priorities, as well as
the traditional threads (which are non-real-time-critical).  Garbage 
collection is done only during thread time, not at task time.  A percentage
of the heap is reserved for tasks, in hopes that they won't need garbage
collection during the time they have the machine.  The OS footprint runs up
to 300 k fully loaded  (but without the java libraries).  Java byte code
is compiled; it is not run as an interpreter.  Although the java byte code
can be produced anywhere, the compiler and debugger are Windows oriented.

T. Morgan discussed the question of real-time usages within the correlator
backend system.  Certainly, the currently most attractive organization for
getting a lot of compute cycles is the Beowolf type clusters, using Linux
PCs with the MPI message passing system for control.  For the most part,
the critical times seem to be of order one second; the response times of
typical real-time systems are more of order a millisecond.  It seems 
advantageous to stick within the Linux context, and not consider other
OSs.  He plans a supervisor process, probably running on a separate machine,
to assign tasks to machines, and maybe attempt dynamic load balancing.


Things we want to know about OS candidates.

Required RT features:
Priorities for tasks (or threads)
Semaphores
Task delay
Periodic scheduling
Message queues (not required, sometimes handy)

Ethernet features:
Support for both IPv4 and IPv6
Socket connection (required)
UDP (both directed and broadcast required)
NFS
FTP (client and server)
rlogin or telnet (client and server)

Memory:
A realistic footprint, with the features and network buffers we would 
   actually use
Is memory mapped?  If so, how do tasks communicate
Is hardware directly addressable from user programs, or must a driver 
   be bound to the OS

Security:
We need something; what do they offer?

Software development:
Languages supported
How are user programs loaded and bound to the OS and to each other
Debugger properties (checkpoint setting required; source level debugger
   and disassembler level debuggers both desirable)

Administrative
How is the OS licensed - object license fee?  developer seat cost? or site 
   license?
For cross-compilers, what systems do they run on?
How is support managed?
BSP availability
OS source code availability