Re: double buffered waveformRecord

[Michael Davidsaver <mdavidsaver@bnl.gov>]

I've posted another iteration.  The changes have actually gotten much 
shorter.

The first patch changes dbAccess.c and arr.c to save the original value 
of DBADDR::pfield before calling get_array_info, then restore it 
immediately after.

http://bazaar.launchpad.net/~epics-core/epics-base/array-opt/revision/12397

The second patch changes waveformRecord.c to allow the safe replacement 
of BPTR whenever the record is locked.  No special allocation, or 
pointer tricks, are needed.

http://bazaar.launchpad.net/~epics-core/epics-base/array-opt/revision/12398

I've also included a (demonstration only) device support which cycles 
through a set of buffers.  Each buffer is written in a dedicated thread 
which passes the buffer pointer to the device support read function 
where it is stored in BPTR (uses I/O Intr scan).  At each iteration the 
value of each array element is incremented by one to allow a client to 
detect dropped or corrupted updates.  This process runs at 1KHz max.

If you want to try it:

cat << EOF > spam.db
record(waveform, "$(P)spam") {
  field(DTYP, "Spam Async")
  field(SCAN, "I/O Intr")
  field(NELM, "$(N=1)")
  field(FTVL, "SHORT")
}
EOF

./bin/$(EPICS_HOST_ARCH)/softIoc -m 'P=x:,N=1000' -d spam.db

http://bazaar.launchpad.net/~epics-core/epics-base/array-opt/revision/12399
http://bazaar.launchpad.net/~epics-core/epics-base/array-opt/revision/12400