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

4 The ALICE Transition Radiation Detector
the hardware on it. It contains the ROC type, the serial number of the ROC and two
structs with information about the ROBs and the ORIs on the ROC.
Most of the sections have one or more variables to store checksums. The checksums
can be used to ensure that no bits have flipped during the transfer from the Command
Coder to the FEEServer. Up to now the checksums are neither created nor checked. The
functionalities are not implemented yet.
One task of the InterComLayer is to compose and send the configuration. But the ICL
has a second task. Each FEEServer publishes 10 DIM data channels: 1 message channel,
1 acknowledge channel, 1 channel containing the FEEServer FSM status, 1 channel for
the DCS board temperature, and 6 channels for voltage sensor readings (see section 4.2).
In total, the TRD has 540 FEEServers running. It turned out that PVSS can handle a
maximum of 1000 changes in the DIM data channels per second. Otherwise it may crash.
The ICL connects to all DIM channels of the FEEServers and re-publishes the channels.
Before re-publishing, it merges all message channels to one channel and suppresses the
voltage sensor channels of the DCS boards which have no sensing wires to the power
bus bars (see section 4.2). The acknowledge channels are handled by the ICL and not
re-published. The ICL takes care that in the re-published DIM channels the maximum
update rate PVSS can handle is not exceeded. Therefore the PVSS program connects
only to the republished channels even if the original channels of the FEEServers are still
available.
Additional monitoring software can either connect to the republished DIM channels or
to the channels provided by the FEEServers. Figure 4.18 shows two examples. A database
which logs all messages from the FEEServers connects to the merged message channel of
the ICL whereas a program monitoring the acknowledge channels has to connect directly
to the FEEServers.
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