Structured beam conditions at CERN-X5A
   ======================================

The orbit period at SPS is 924 BX, whereas LHC is 3564.
Given that all trigger boards are to check their sync with BC0
every orbit, ALL boards (especially trigger boards) have to
modify their BX counters to count to 924 (or rather 0 to 923).

SPS beam conditions at X5A for reference:
	beam clock = 24.95 ns (better than 100 ppm)
	~2.3 ns wide bunches (at the base)
	~16.8 sec period for ramp/spill cycle
	~1.5-2.5 spill duration
	~23 usec orbit period during spill (exactly 924 BX, 0 to 923)
		* not constant outside of spill *
	1 filled train per orbit
	48 filled bunches in one train (~1200 ns)
	muon rate up to ~10^4 per spill
	pion rate up to ~10^6 per spill
Note that this is PER SPILL, not per second.  Actually, I have anecdotal
evidence that these rates will be about a factor of 10 LOWER during
structured beam!  Therefore any high-rate tests should be done with a
"normal" beam.  Pleas see the beam schedule in another document.

We WILL NOT have uniform BC0 between spills; therefore we WILL need
to reset our BX counters between spills.  This must be an automatic
procedure executed regularly after every spill.  The TTC will do this
using the orbit and spill signals as input for the B-Go signals.  In
this way we can get the LHC-like response we need.  Sang-Joon Lee from
Rice has written some TTCvi control programs to do this for us.