MCM numbering in the gateDB
===========================


The situation
-------------

So far, there is no non-ambiguous numbering and identification scheme
for MCMs: the TRAP ID, while possibly unique, is often written into
the chip with errors, so that this laser number, when read from the
TRAP, is no longer unique. On the other hand, the MCM "IDs",
consisting of a nutzen number and the location within the nutzen, are
also not unique, because some nutzen numbers were used twice.

In the original implementation of the gateDB, it was not yet known
that the MCM ID is ambiguous, and this number was chosen as a primary
key for the table of MCMs. Later, an example of an ambiguous MCM ID
was found, and a workaround (a.k.a. a dirty hack) had to be
implemented to cope with this problem: if a non-unique MCM ID was
found, the second MCM was assigned an artificial number (999xxxx) as
the MCM ID, losing the information about which MCM this might have
been.

As some problems came up with the entering of MCMs into the DB, it was
decided to change the gateDB to handle these numbers in a cleaner way
(August 2007).


Numbers in the gateDB
---------------------

laser_num is the number read out from the TRAP chip by software, this
should be the same number as the TRAP ID if no write errors occured,
but this has not been checked. As this is is the only number
accessible by software, it is an important means of automatically
identifying an MCM. However, due to write errors, the number is
ambiguous, and not usable as a primary key for a DB. The laser_num is
always less than about 260000 (0x3FFF), due to the number of bits
available in the TRAP.

label_num is what was formerly referred to as the MCM ID. As the old
MCM IDs turned out not be be unique, they can no longer be used as
primary keys, but only as a second, less ambiguous way to identify and
MCM than the laser_num. The name label_num is due to the number being
printed on the label on each MCM. This number consists of a batch
number (1 digit), a nutzen number (4 digits) and a position on the
nutzen (2 digits between 1 and 4).

mcm_id is an artificial MCM number, generated automatically by the
RDBMS. It has no meaning in real life, and is only used for internal
bookkeeping.



Entering MCMs into the gateDB
-----------------------------

As there does not seem to be a production log specifying the MCMs used
for each ROB, this information has to be entered at one stage of
testing the ROBs. Historically this was the ROC test stand, because
this is where the software was first developed, but it should be done
in the ROB tester, because reading the numbers on the labels is
simpler there.

The numbers are entered into the gateDB with a script called
check_laser_ids.pl, which is now available in version 2.0.

The script parses a logfile of a test, containing information about
which laser ID was read from each MCM on a ROB. For each MCM, it first
checks if there is already an MCM in this position, and compared the
laser ID from the DB with the one from the logfile. If the numbers are
the same, it assumes that the information in the DB is correct and
goes to the next one to avoid unnecessary updates of the DB.

If the laser IDs differ, or if the position is not yet occupied by an
MCM in the DB, the script tries to determine the MCM label number from
Stefan's MCM DB using the test data from the MCM test stand in
Karlsruhe, provided by Venelin. If only one MCM is found that has this
laser ID, the script assumes that this is the correct label number and
enters an MCM with this label_num and the laser_num from the logfile
into the gateDB. If there is no MCM with this laser ID, the user is
asked to enter the MCM as printed on the label by hand. This case
usually indicates that not all test results have been uploaded to the
MCM DB, and Stefan and/or Venelin should be contacted to update the
MCM DB. If several MCMs have been found with the same laser number,
the user is given a list of possible MCM label numbers to chose from,
or can still enter the number by hand. 

After the user has entered the MCM label number, an entry for the MCM
is inserted with this number and the laser number from the logfile. If
another MCM was located at this position before, it is relocated to a
location called "removed mcm", indicating that this MCM has probably
been removed in the repair of a ROB.