The FEE Server Control Engine of the ALICE-TRD - Westfälische ...

4 The ALICE Transition Radiation Detector
channels which fulfil configurable conditions like the channel being part of a tracklet or
the total signal sum is above a threshold are send.
The MCMs have no nonvolatile memory. Therefore the complete configuration has to
be transmitted to the MCMs after each power up. This includes calibration values for
the ADCs, the filter settings and settings for the tracklet preprocessor. The settings are
transmitted to the MCMs via the SCSN bus and written to the configuration registers of
the TRAP chip. The TRAP chip has 434 configuration registers in total with sizes between
1 and 32 bits [A + 05]. Not all registers are used to store configuration values. Writing to
some registers initiates special actions of the TRAP like reading the internal temperature
sensor (see chapter 6) whereas other registers contain counters or status information of
the chip. A complete list of all registers, their individual size and their function is given
in the TRAP user manual [A + 05].
The four tracklet processors which do the tracklet calculation are freely programmable
CPUs. Each CPU has an instruction memory (IMEM) of 4096 times 24 bit (4096 ’words’)
which contains the program for the CPU. Just like the configuration, the programs for the
CPUs have to be transmitted to the MCMs via the SCSN Bus. The current programs have
a size of 1532 words for the first CPU, 1665 words for the second CPU, 1367 words for
the third CPU and 1412 words for the forth CPU. Most parts of the four CPU programs
are identical. The different sizes of the configurations are caused by the fact that the
programs do not only contain the routines for the tracklet calculation but test routines
and other special functions, too. Since there is space left in the IMEM the programs can
be extended in the future.
4.3.3 The Optical Readout Interface
The Optical Readout Interface (ORI) is an optical transmitter card which transfers the
data from the MCMs to the global tracking unit (GTU). The ORI receives the data from
the half chamber merger (see 4.3.6), converts and serializes the data and sends it via an
optical fiber at 2.5 Gbit/s to the GTU.
The four main components of an ORI are a CPLD chip (Complex Programmable Logic
Device) which provides the interface between the half chamber merger and a serializer
chip, the serializer chip, an optical driver chip for the laser diode and the diode itself.
The ORI has a JTAG and an I 2 C interface. The JTAG interface provides access to the
CPLD chip. It can be used to reprogram the CPLD and to access some configuration
registers in the CPLD. The I 2 C interface is used to program and control the laser driver
chip [LARP06].
Two MCMs on each ROB equipped with an ORI support a special operation mode. In
this mode commands addressed to these MCMs are forwarded via JTAG or I 2 C to the
ORI. Data from the ORI are received by the MCMs and stored in registers of the MCMs
where they can be read out via SCSN. Using these MCMs, programs running on the DCS
board have access to the CPLD and the optical driver chip on the ORI. To avoid access
conflicts both MCMs must not be in the special operation mode at the same time.
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