Re: SCSI disk problems - Don't know where to begin

[jhassett@my-dejanews.com]

In article <70lj95$s66$1@nnrp1.dejanews.com>,
  krichey@nswc.navy.mil wrote:
> I am writing some data extraction code in Ada (Greenhills) in a VxWorks,
> PowerPC, VME card cage system, with a SCSI disk.  VME-167 cards
> Also there are some C tasks.
>
> At some point (it varies, and doesn't happen every time) the best we can tell
> our SCSI disk is waiting on an interrupt and hanging.  My Ada task is
> just sitting there taking minutes for individual i/o statements to complete.

A couple of our projects are working with Green Hills Ada and VxWorks,
and PowerPC is one of their targets.  I've heard that the restrictions
imposed on interrupt services routines by VxWorks lead to serious
limitations on any Ada subprograms called in the interrupt state.
Perhaps you know about this, but just in case you don't, here is my
understanding of the situation:

Under VxWorks, interrupts are handled outside of any (VxWorks) task's
context.  This is evidently done to avoid the overhead of task context
switching.  Unfortunately, the Green Hills Ada compiler seems to be
designed with the assumption that there is always a task ID available,
but this is not true in the interrupt state.  Besides the usual
restrictions imposed by VxWorks (no blocking operations, no I/O through
device drivers, no FP coprocessor operations), we've been told by
Green Hills that subprograms called in the interrupt state must not
have exception handlers, and must be compiled with runtime checks
suppressed.  Apparently there are attempts to access the task control
block when setting up exception handling or when preparing to do the
runtime checks.

I have no idea whether a failure to comply with these restrictions could
lead to the symptoms you've seen, but you need to know about this in any
case.

- Jim Hassett

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