Draft 0.93

                 Track Segment Finder to Level 3 Trigger

                         Interface Specification

                            July 28, 1997


The Track Segment Finder (TSF) in the Level 1 Drift Chamber Trigger
generates track segment addresses and time stamps, transmitted to the
TSF Readout Module (ROM).  The ROM performs zero suppression,
formatting and any additional processing needed by downstream
consumers such as the Level 3 trigger.  This specification outlines
the special needs of Level 3 (L3) as imposed on the TSF.

Minimal data content to be transmitted
______________________________________

16-bit segment address
time stamp (since arrival of L1Accept signal at TSF)

These data should be zero-suppressed for speeding up subsequent
unpacking, meaning a list containing non-zero segments are to be
delivered (not the full fixed-length record that is transmitted from
the TSF Module to the ROM).

Additional data derived in the ROM
__________________________________

Look-up-table (LUT) information based on address:
 phi relative to wire or in absolute coordinate system (radians)
 slope relative to radial (radians)
 correlation matrix [dphi, dslope, correlation]
Estimated event T0 (ns)
Two hitmaps in phi based on segments in A4 at two different phi resolutions,
nominally or order 1 and 10 degrees.

The estimated event T0 is needed in the fast Svt track finder to
restrict the number of Svt time ticks in which to search by roughly a
factor of 5 to 10 leading to improved speed and, effectively, reduced
occupancy.  T0 will likely be of use many places downstream, and thus
is best computed once, as a central resource.  [Other L3'ers: please
add your name to this list so that the word "likely" can be removed.]

The phi hit-maps in A4 are used to select only those track candidates
in the Svt which are in coincidence with segments in the DCH after
extrapolation from the SVT.  If the hit-maps are built in the TSF
readout as it scans the TSF data, the L3 Svt filter will not need to
unpack the DCH data, improving its speed, yet there should not be much
burden on the segment readout.  Actual speed measurements are not yet
available, so this is a requirement based on intuition that will be
demonstrated more fully in the future.

The need for the other quantities is yet to be demonstrated.

Formatting
__________

Name			Format		Unit

16-bit address		int, 2 bytes
time stamp		int, 1 byte	3.7 MHz ticks
			or
			float		nanoseconds or seconds

Order of packing makes a difference in speed of unpacking, to be
determined.