This file describes a few of the things that it is important to
remember about the L1.5 Cal Trig Local/Global DSP code:

                                                            24-OCT-1994 


(1)     The RefSet energy comparisons are done via a GREATER THAN 
        comparison in the DSP Frame Code, while the sense of the comparison
        specified by COOR is GREATER THAN OR EQUAL TO.  Recall that COOR
        specifies the RefSet Et's in GeV, while the DSP code only knows
        about counts.  The TCC must translate GeV into counts when down-
        loading RefSets to the L1.5 Cal Trig code.  The TCC is also
        responsible for providing a correct count value to allow the 
        DSP GREATER THAN comparison to correctly reflect the COOR-
        specified GREATER THAN OR EQUAL TO comparison.

        If the TCC sets a Ref Set value of 255 counts, the corresponding
        Trigger Tower is excluded, because the maximum TT Et is 255 counts.
        (recall that TT Et is stored as an 8-bit unsigned integer).


(2)     The DSP code does not need to correct the TT Et for Lookup Zero
        Response (pedestals) before performing the RefSet energy comparison.  
        That is, the TCC has already included (added) the pedestals when 
        specifying RefSet energies to the DSPs.  The DSP does not need to 
        modify the stored RefSet energies (either during initialization or
        "on the fly").

        Note that there is one open delay slot left in the Scan Routine that
        could be used for "on the fly" modifications (of either TT or RefSet
        Data) with no performance hit if we chose to do that.


(3)     No attempt is made to eliminate "double-counting": if the Et in
        each of two neighboring towers is above the Reference Set Et,
        each Tower has a chance to produce an object in a Local DSP
        Object List, even if both Towers are actually part of the same
        "object."  

        This could be done in either the Frame (time-consuming) or the
        Tool (either Local or Global).  For electrons, the Tool could
        for example fail the object if any neighboring Tower has a higher
        Et than the seed Tower.


(4)     Regardless of the Total Et Energy Scale coming from the CTFEs, the
        Energy Scale of all output from the Local DSPs (and thus the Global
        DSP) will be 1/4 GeV per count, and will have no pedestal (thus
        it needs to be a signed quantity).  


(5)     The "DSP ID" is an 8-bit quantity.  Since the DSP ID's are constrained
        to be in the set:

            {A | B | C} {1 | 2 | 3 | 4}     (i.e. A1..C4)

        I have stored the DSP ID in HEX as $A1, $A2, etc.  This fits the
        8 bit field available.

  
(6)     The DSP's and 68K_Service_CPU exchange a byte of TAS with each
        message to allow for synchronization checking.  This TAS byte
        is also included at the end of the Data Block for consistency
        checking.
        

(7)     There will be NO entries in the Global Object List, but the
        Header Word will indicate how many Objects were found.