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

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} 5 The FEEServer Control Engine mcm_info [ s l ] . hopcount = mcm_info [ s l ] . l i n k =0; s l _ l e f t * 2 − s l −1; } i f ( s l >= s l _ r i g h t ) { mcm_info [ s l ] . dest = no_of_slaves − s l +1; mcm_info [ s l ] . hopcount = ( no_of_slaves−s l _ r i g h t ) * 2 − ( no_of_slaves−s l ) ; mcm_info [ s l ] . l i n k =1; } broadcast_info . data [ 0 ] . hopcount_write= s l _ l e f t * 2 −1; / / l e f t p a r t o f t h e l i n k p a i r broadcast_info . data [ 1 ] . hopcount_write =( no_of_slaves − s l _ r i g h t ) * 2 +1; / / r i g h t p a r t o f t h e l i n k p a i r Listing 5.3: Code to recalculate the slave IDs of the MCMs and the broadcast hopcounters in case of a bridged linkpair. sl is the slave ID of the MCM in an unbridged linkpair, no_of_slaves the total number of MCMs in the linkpair (34 or 36), sl_left the number of MCMs in the ’left’ part and sl_right the number of MCMs in the ’right’ part of the linkpair When the calculation is finished the control flow returns to learnConfig() of SCSNBus. At this point it is known which MCMs have to be bridged but the MCMs themselves are not bridged yet. The function SCSNBus::learnConfig() calls * SCSNBusBridge::getSlavesToBridge (void) for each linkpair to get the list of MCMs to bridge. In each linkpair either no, one, or two MCMs have to be bridged. The function SCSNBus::learnConfig() creates the correct SCSN commands and sends them to the MCMs (see next section). If no MCMs have to be bridge this step is skipped. Afterwards the configuration process is finished and the control flow returns to the function which has called SCSNBus::learnConfig(). 5.3.2 Access Synchronisation In the FEEServer two threads run in parallel. One thread handles commands and configurations received from the ICL and the other thread monitors the DCS board sensors and the MCM temperature sensors. At this point a problem occurs. The sensor readout in the second thread runs independently of command handling thread but both threads need hardware access. Neither can the SCSN bus be accessed by both threads at the same time nor is it possible to read out the DCS board sensors and access the SCSN bus in parallel. To solve this problem the mutex mechanism 6 is used. In the control engine the mutex administration and the interface to open and close the SCSN Bus are encapsulated in the class SCSNGuardian (libTRD). The constructor of SCSNGuardian locks the mutex and opens the SCSN bus interface and the destructor unlocks the mutex and closes the SCSN bus interface. Each time a thread needs SCSN bus 6 The mutex mechanism is a programming technique for inter-thread synchronization. One thread locks the mutex as soon as it enters a function block which cannot run in parallel. If the other thread now tries to lock the mutex because it also enters a function block which cannot run in parallel, this thread is stopped as long as the mutex remains locked. When the mutex is now unlocked by the first thread the second thread can lock the mutex and continues execution. 64
5 The FEEServer Control Engine access it creates an instance of SCSNGuardian. After the access is not needed anymore the thread deletes the instance. Using the destructor to unlock the mutex has an advantage. When a function that locked the mutex is left, the mutex is released, independent of how the function is left – by a usual return or by throwing an exception. 5.3.3 Sending of SCSN Commands SCSNBus::execute() next linkpair SCSNBus::selectLinkpair() SCSNBus::processCmds() different conversion functions alimcm2slave() SCSNBusBridge::querySlave() create the frame and store it in the send buffer SCSNBus::sendFast() SCSNBus::sendFastNow() SCSNBus::checkFrames() SCSNBus::copyFrameData() Figure 5.7: Control flow within the SCSN Bus class system for sending SCSN commands. The control flow (solid arrows) is simplified and only the main stepts are shown. The dashed lines are for better orientation only. The class SCSNBus provides the public function void execute(struct cfdat_command * , unsigned, int) to send a list of SCSN commands. The first parameter is a pointer to the list 65
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1 Introduction The standard model o
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2 Theoretical background first gene
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Temperature (MeV) 225 200 175 150 1
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