PH> Unforunately, ditching PM/WPS removes one of the best features of 
 PH> OS/2.  My reasons for trying to move to OS/2 _include_ the great 
 PH> interface so I'd be unhappy to have to give it up.  You're right 
 PH> that would avoid the problems with long interrupt disable paths 
 PH> in some of the PM code, though.  Maybe a good
 PH> stop-gap measure.

Any important control system with critical timing needs a dedicated
processor to avoid disruption from other processes. This would be true if
the operating system was custom, OS/2, Unix, or DOS. Ideally, the user
interface and monitoring processes can be moved to another processor to
bring the control process totally under the programmer's control.

There are two basic options to consider. 

 1. A processor board on the PC bus. Control program in Firmware with 
    control options modified from the PC. This is simple to design. The
    problems are that the control processor is not totally independant
    of the PC. The off switch, reset switch and CTL-ALT-DEL will still
    effect the control system.

 2. A separate system communicating with a PC via RS-232, RS-485, or 
    network adapter. This separate system could be as simple as a 
    embedded controller or as complex as a PC. The OS/2 kernel without
    WPS or PM would be an ideal candidate for a PC. This stand alone
    approach allows the control system total independence from the
    PC user. A rack mount PC with controlled power and access is the
    top of the line approach. Again, the user interface is isolated from
    the controlling computer.

I favor the second configuration using PC's for both the user interface and
the controller. It is cost effective. Very little hardware design, if any,
is needed. The interface I prefer is network adapter as additional PC's can
be brought into the system as back-up control points or monitoring or
replaccements with little interruption. The networking must be done on a
separate segment or ring from the rest of the network in the building to
avoid problems encountered in the larger environment.

If a system is so critical that microsecond timing is important, the two PC
approach should be able to be cost justified. And remember, with OS/2 the
user interface PC can be logged onto two separate networks with two
separate adapters. This enables the PC to either be used as a general
workstation on the main LAN or bridge information from the control PC onto
the main LAN or both.

Carl

--- FleetStreet 0.90wb