[Simh] PCAP for OpenVMS/Alpha

[Matt]

I'm not sure how many people have tried the PCAP port for OpenVMS/Alpha
but I've never been able to get it to work (and no-one I know has been
able to get it to work). After much debugging with XDELTA i've
determined the following modification is needed in  PCAPVCM.C:

#pragma linkage pcap_evtLnkg = (parameters(r4,r1, r2), preserved(r5),
nopreserve(r0,r1))

should be:

#pragma linkage pcap_evtLnkg = (parameters(r4,r1, r2), preserved(r4,r5),
nopreserve(r0,r1))

This prevents corruption of R4 when pcap_event is called from
LAN$COMPLETE_VCRP. I've tested this on a PWS 500au and a DS25 and all
seems ok. There are a few other fixes needed to the descrip.mms for the
VMS port and i'll post these soon.

I'm attempting a port to OpenVMS/IA64, watch this space...

Matt