Universe VME notes (was Re: BSP for Motorola MVME5500)

[Feng, Shuchen]

Till Straumann wrote:

> You would have to either disable posted writes (incurring
> a significant performance penalty) altogether or set up
> secondary VME windows with PWEN cleared. This would be more
> elegant but doesn't fit the EPICS devLib API.

I had tried to disable the posted writes prio to 'write probes', and
reenabled the posted writes after 'write probes' to avoid
the performance penalty.  However, it did not work.
 

 > 2) Some hardware (such as the MPC106 hostbride on my SVGM board)
 >    doesn't even bother to support raising machine check exceptions
 >    on failing VME writes.

Ditto MVME5500. The EMCP signal is pulled up high and not used.

> It is recommended to exclusively use 'read probes' for device detection.

Great!  This takes out one struggle from my TODOs.

Thanks a lot,
Kate